Milk Production and Fertility in Cattle

Archetypal clustering reveals physiological mechanisms linking milk yield and fertility in dairy cattle

Fertility in dairy cattle has declined as an unintended consequence of single-trait selection for high milk yield. The unfavorable genetic correlation between milk yield and fertility is now well documented; however, the underlying physiological mechanisms are still uncertain. To understand the relationship between these traits, we developed a method that clusters variants with similar patterns of effects and, after the integration of gene expression data, identifies the genes through which they are likely to act. Biological processes that are enriched in the genes of each cluster were then identified. We identified several clusters with unique patterns of effects. One of the clusters included variants associated with increased milk yield and decreased fertility, where the "archetypal" variant (i.e., the one with the largest effect) was associated with the GC gene, whereas others were associated with TRIM32, LRRK2, and U6-associated snRNA. These genes have been linked to transcription and alternative splicing, suggesting that these processes are likely contributors to the unfavorable relationship between the 2 traits. Another cluster, with archetypal variant near DGAT1 and including variants associated with CDH2, BTRC, SFRP2, ZFHX3, and SLITRK5, appeared to affect milk yield but have little effect on fertility. These genes have been linked to insulin, adipose tissue, and energy metabolism. A third cluster with archetypal variant near ZNF613 and including variants associated with ROBO1, EFNA5, PALLD, GPC6, and PTPRT were associated with fertility but not milk yield. These genes have been linked to GnRH neuronal migration, embryonic development, or ovarian function. The use of archetypal clustering to group variants with similar patterns of effects may assist in identifying the biological processes underlying correlated traits. The method is hypothesis generating and requires experimental confirmation. However, we have uncovered several novel mechanisms potentially affecting milk production and fertility such as GnRH neuronal migration. We anticipate our method to be a starting point for experimental research into novel pathways, which have been previously unexplored within the context of dairy production.

Intake profile, milk production and energy balance of early lactation spring calving Holstein Friesian and Jersey x Holstein Friesian dairy cows in high utilisation pasture-based systems

Early lactation is a critical period for dairy cows as energy requirements rapidly increase with the onset of lactation, however, early lactation dry matter intakes (DMI) in pasture-based systems are under-measured. The objectives of this study were 1) to measure and profile total DMI (TDMI) and animal performance of dairy cows during early lactation in a pasture-based system 2) to investigate early lactation energy balance in pasture-based systems and 3) to examine production efficiencies including TDMI and milk solids production per 100 kg bodyweight. Eighty spring-calving dairy cows were allocated to a grazing group as they calved over a 2 year period (2021 and 2022). Cows were offered a daily herbage allowance to achieve a post-grazing sward height of 4 cm with silage supplementation when necessary due to inclement weather. Total DMI was measured using the n-alkane technique over a 12 week period from 1st of February to the 23rd of April. Total DMI and daily milk yield were significantly affected by parity with both variables being greatest for third parity animals (17.7 kg DM and 26.3 kg/cow/day, respectively), lowest for first parity (13.2 kg DM and 19.6 kg/cow/day, respectively) and intermediate for second parity animals (16.8 kg DM and 24.1 kg/cow/day, respectively). Peak TDMI was reached on wk 10 for first parity animals (14.6 kg DM), wk 11 for second parity animals (19.3 kg DM) and wk 12 for third parity animals (19.9 kg DM). Parity also had a significant effect on UFL (feed units for milk) feed balance as first parity animals experienced a greater degree of negative energy balance (-3.2 UFL) compared with second and third parity animals (-2.3 UFL). Breed and parity had an effect on production efficiencies during the first 12 weeks of lactation as Jersey x Holstein Friesian cows had greater TDMI/100 kg bodyweight and milk solids/100 kg bodyweight compared with Holstein Friesian cows.

Genetic parameters for milk yield and reproductive traits in Honduran Holstein cattle

The aim of this study was to estimate the (co)variance components and genetic parameters for milk yield adjusted to 305d (MY305), calving-to-conception interval (CCI), number of services per conception (NSC) and calving interval (CI) of Honduran Holstein cows, by fitting a bivariate animal model using Maximum Restricted Likelihood procedures. Model included the fixed effects of calving number, the contemporary calving group (farm-season-year of calving and the cow age as covariate). The estimated means and standard deviations for MY, CCI, NSC and CI were, 5098.60 ± 1564.32 kg, 168.27 ± 104.71 days, 2.46 ± 1.69 services, and 448.73 ± 109.16 days, respectively; and their estimated heritabilities were 0.21 ± 0.05, 0.03 ± 0.028, 0.02 ± 0.024 and 0.06 ± 0.04, respectively. The genetic correlations between MY305 and CCI, NSC and CI were positive and antagonist, with values of 0.64 ± 0.52, 0.99 ± 0.56, and 0.32 ± 0.24 respectively. Even though moderate to low heritability was estimated for MY305, systematic selection for milk yield, with a reduction in reproductive efficiency, if considered as the only selection criterion is important to be considered. By including reproductive traits and considering permanent environment effects into the breeding program, might yield a slow, but constant and permanent improvement over time.

A comprehensive meta-analysis of genetic parameters for resilience and productivity indicator traits in Holstein cattle

Selection for resilience indicator (RIND) traits in Holstein cattle is becoming an important breeding objective as the worldwide population is expected to be exposed to increased environmental stressors due to both climate change and changing industry standards. However, genetic correlations between RIND and productivity indicator (PIND) traits, which are already being selected for and have the most economic value, are often unfavorable. As a result, it is necessary to fully understand these genetic relationships when incorporating novel traits into selection indices, so that informed decisions can be made to fully optimize selection for both groups of traits. In the past 2 decades, there have been many estimates of RIND traits published in the literature, albeit in small populations. To provide valuable pooled summary estimates, a random-effects meta-analysis was conducted for heritability and genetic correlation estimates for PIND and RIND traits in worldwide Holstein cattle. In total, 926 heritability estimates for 9 PIND and 27 RIND traits, along with 362 estimates of genetic correlation (PIND × RIND traits) were collected. Resilience indicator traits were grouped into the following subgroups: Metabolic Diseases, Hoof Health, Udder Health, Fertility, Heat Tolerance, Longevity, and Other. Pooled estimates of heritability for PIND traits ranged from 0.201 ± 0.05 (energy-corrected milk) to 0.377 ± 0.06 (protein content), while pooled estimates of heritability for RIND traits ranged from 0.032 ± 0.02 (incidence of lameness, incidence of milk fever) to 0.497 ± 0.05 (measures of body weight). Pooled estimates of genetic correlations ranged from -0.360 ± 0.25 (protein content vs. milk acetone concentration) to 0.535 ± 0.72 (measures of fat-to-protein ratio vs. milk acetone concentration). Additionally, out of 243 potential genetic correlations between PIND and RIND traits that could have been reported, only 40 had enough published estimates to implement the meta-analysis model. Our results confirmed that the interactions between PIND and RIND traits are complex, and all relationships should be evaluated when incorporating novel traits into selection indices. This study provides a valuable reference for breeders looking to incorporate RIND traits for Holstein cattle into selection indices.

Unveiling the Role of IGF-I in Fertility: Effect of Long-Acting Bovine Somatotropin (bST) on Terminal Follicular Development and Fertility during an Annual Reproductive Cycle in Sheep

The study aimed to assess the effect of long-acting bST treatment, in a dose that only increases IGF-I plasma concentrations, on ovarian and fertility markers of estrous synchronized ewes that were fed to keep their bodyweight. Three experiments were designed to evaluate this effect: in Experiment 1, 18 ewes were distributed in groups (bST 0, 30, 50 mg) to measure plasma IGF-I and insulin for 15 days; in Experiment 2, 92 ewes (5 replicates) in two groups (0 and 30 mg bST) were synchronized using a 6-day progesterone protocol during the breeding season to assess the effect of bST on follicular and luteal performances, estrous and ovulation, and fertility after mating. In Experiment 3, 50 ewes (3 replicates) were used to repeat the study before but during anestrus. Results indicate that 50 mg bST increased IGF-I and insulin plasma concentrations, but 30 mg bST only increased IGF-I concentrations; and that only during the breeding season did 30 mg bST increase the number of lambs born and the reproductive success of ovulatory-sized follicles compared to controls. This occurred without it affecting any other reproductive marker. In conclusion, 30 mg bST treatment may improve oocyte competence for fertility during the breeding season.

Developmental programming of reproduction in the female animal

Successful reproduction is a cornerstone in food animal industry in order to sustain food production for human. Therefore, various methods focusing on genetics and postnatal environment have been identified and applied to improve fertility in livestock. Yet there is evidence indicating that environmental factors during prenatal and/or neonatal life can also impact the function of reproductive system and fertility in the animals during adulthood, which is called the developmental programming of reproduction. The current review summarizes data associated with the developmental origins of reproduction in the female animals. In this regard, this review focuses on the effect of plane of nutrition, maternal body condition, hypoxia, litter size, maternal age, parity, level of milk production and milk components, lactocrine signaling, stress, thermal stress, exposure to androgens, endocrine disrupting chemicals, mycotoxins and pollutants, affliction with infection and inflammation, and maternal gut microbiota during prenatal and neonatal periods on the neuroendocrine system, puberty, health of reproductive organs and fertility in the female offspring. It is noteworthy that these prenatal and neonatal factors do not always exert their effects on the reproductive performance of the female by compromising the development of organs directly related to reproductive function such as hypothalamus, pituitary, ovary, oviduct and uterus. Since they can impair the development of non-reproductive organs and systems modulating reproductive function as well (e.g., metabolic system and level of milk yield in dairy animals). Furthermore, when these factors affect the epigenetics of the offspring, their adverse effects will not be limited to one generation and can transfer transgenerationally. Hence, pinpointing the factors influencing developmental programming of reproduction and considering them in management of livestock operations could be a potential strategy to help improve fertility in food animals.

Developmental programming of production and reproduction in dairy cows: III. Association of level of maternal milk production with offspring's birth weight, survival, productive and reproductive performance and AMH concentration from birth to the first lactation period

Although some studies investigated the relationship of dam milk production (DMP) with offspring birth weight and productive performance, limited information is available on the association of level of DMP with reproductive performance in dairy cows. Therefore, the present study was conducted to understand whether dams with various levels of milk production produce offspring with different fertility. In study I, offspring were classified based on the level of DMP into five categories, including DMP1 (dams with <10.00 × 103 kg of 305-day milk production), DMP2 (dams with ≥10.00 × 103 kg and <12.00 × 103 kg of 305-day milk production), DMP3 (dams with ≥12.00 × 103 kg and <14.00 × 103 kg of 305-day milk production), DMP4 (dams with ≥14.00 × 103 kg and <16.00 × 103 kg of 305-day milk production) and DMP5 (dams with ≥16.00 × 103 kg of 305-day milk production). In study I, data of birth weight, milk yield and reproductive variables of 14,536 offspring born to lactating dams and corresponding data of DMP were retrieved. In study II, blood samples (n = 339) were collected from offspring in various categories of DMP for measurement of serum AMH. Offspring were heavier at birth in DMP4 and DMP5 categories than DMP1 and DMP2 categories (P < 0.05). Milk yield of offspring increased as DMP elevated (P < 0.05); however, offspring in DMP1 and DMP2 categories produced higher milk as compared with their dams during primiparity (P < 0.05) whereas offspring in DMP3, DMP4 and DMP5 categories produced less milk as compared with their dams during primiparity (P < 0.05). Milk fat to protein ratio during the first month of lactation was greater in DMP4 and DMP5 categories than DMP1 category (P < 0.05). Offspring of DMP4 and DMP5 categories were inseminated and conceived at younger ages than offspring of DMP1 category during nulliparity (P < 0.05). Calving to conception interval was longer in DMP5 than DMP1 category in primiparous offspring (P < 0.05), but concentration of AMH did not differ among various categories of DMP (P > 0.05). In conclusion, dams with greater level of milk production produced heavier offspring with higher milk yield but worse transgenerational improvement in milk production and diminished reproductive performance, which were seemingly under higher pressure of negative energy balance during the first month of lactation.

Association between genomic daughter pregnancy rate and expected milk production on the resumption of estrus behavior in Holstein cattle

The objective of this observational study was to evaluate estrous expression at the first estrus occurring between 7 to 30 d in milk (DIM), as detected by an automated activity monitor (AAM), and its association with genomic daughter pregnancy rate (GDPR) and genomic expected milk production (GEM) in lactating dairy cows. A total of 4,119 lactations from 2,602 Holstein cows were included. Cows were enrolled as first lactation (n = 1,168), second lactation (n = 1,525) and third and greater lactation (n = 1,426). Hair samples were collected from the tail switch, and cows were genotyped using an SNP platform (Clarifide, Zoetis, São Paulo, SP, Brazil). Postpartum cows were examined daily by the farm personnel from calving until 10 DIM. Calving was classified as assisted (forced calf extraction) and unassisted (normal calving). Retained fetal membranes (RFM), hyperketonemia (KET), and left displaced abomasum (LDA) were also recorded. Mean GDPR (± SD) was -0.29 ± 1.4, and the intensity and duration of the first estrus event was 15.9 ± 13.1 x-factor (intensity unit measurement) and 11.1 ± 3.8 h, respectively. Cows that had greater GDPR had greater intensity and longer duration of estrus at the alert, independent of parity. Overall resumption of estrous expression, between 7 to 30 DIM, was 41.2% (1,695/4,119), where 58.8% (2,424/4,119) did not have an estrus event, 31.0% (1,274/4,119) of cows had one event of estrus, and 10.2% (421/4,119) of cows had 2 or more events of estrus early postpartum. Mean DIM (± SD) at first estrus event, detected by the AAM, was 19.4 ± 4.4 d. Days in milk at first event for cows with one event was 20.7 ± 1.6 d and 15.9 ± 3.1 d for cows with 2 or more events of estrus. First lactation cows were more likely to have an estrus event early postpartum when compared with second and third and greater lactation cows (45.2 ± 1.4% [530/1168] vs. 41.6 ± 1.3% [636/1525] vs. 37.2 ± 1.3% [529/1426], respectively). There was an interaction of parity and GDPR on the proportion of cows demonstrating an early postpartum estrus. There was no difference in the proportion of cows with an early postpartum estrus between those with assisted or unassisted calving, RFM, or LDA. However, cows that had KET were less likely to have an alert early postpartum when compared with cows that did not have KET. Mean genomic expected milk production (± SD) was 256.8 ± 600.1 kg. There was no interaction between GEM and parity on estrous expression (i.e., intensity and duration). There was no interaction between GEM and GDPR on the proportion of estrus early postpartum.

Bovine FRAS1: mRNA Expression Profile, Genetic Variations, and Significant Correlations with Ovarian Morphological Traits, Mature Follicle, and Corpus Luteum

The amelioration of bovine fertility caused by a multi-factorial problem has always been a hot topic, among which the detection of available target genes is the most crucial. It was hypothesized that the Fraser extracellular matrix complex subunit 1 (FRAS1) gene detected by GWAS is involved in physiological activities such as ovarian development. Herein, unilateral ovaries from 2111 cows were used to examine the mRNA expression profile and polymorphisms of bovine FRAS1 and their associations with fertility-related characteristics. Firstly, it was confirmed that FRAS1 gene transcripts are expressed in various bovine tissues. Then, among five potential insertion-deletion (indel) loci, the 20 bp (named P3-D20-bp) and 15 bp (P4-D15-bp) deletion mutations were confirmed to be polymorphic with linkage equilibrium. Secondly, the P3-D20-bp polymorphism was significantly associated with ovarian weight and corpus luteum diameter in the metaestrus phase and ovarian length in the dioestrum stage. Additionally, both ovarian length and mature follicle diameter in metaestrus are significantly correlated with different genotypes of P4-D15-bp. Thirdly, the transcriptional expression of the FRAS1 gene in groups with a minimum value of ovarian weight or volume was significantly higher than the expression in groups with a maximum value. Instead of that, the more corpus luteum and mature follicles there are, the higher the transcription expression of the FRAS1 gene is. Furthermore, FRAS1 expression in cows with a heterozygous genotype (ID) of P3-D20-bp was significantly higher than others. Eventually, P3-D20-bp deletion could disturb the binding efficiency of WT1-I and Sox2 to FRAS1 sequence according to binding prediction, indicating that mutation may affect gene expression and traits by influencing the binding of transcription factors. Overall, the polymorphisms of P3-D20-bp and P4-D15-bp of the bovine FRAS1 gene significantly correlated to follicle or ovarian traits that could be applied in optimizing female fertility in cow MAS breeding programs.

DNA methylation profiles in bovine sperm are associated with daughter fertility

The current decline in dairy cattle fertility has resulted in significant financial losses for dairy farmers. In the past, most efforts to improve dairy cattle fertility have been focused on either management or genetics, while epigenetics have received less attention. In this study, 12 bulls were selected from a provided 100 bull list and studied (High daughter fertility = 6, Low daughter fertility = 6) for Enzymatic methylation sequencing in the Illumina HiSeq platform according to the Canadian daughter fertility index (DFI), sires with high and low daughter fertility have average DFI of 92 and 112.6, respectively. And the bull list provided shows a mean DFI of 103.4. 252 CpGs with methylation differences greater than 20% (q < 0.01) were identified, as well as the top 10 promising DMRs with a 15% methylation difference (q < 1.1e-26). Interestingly, the DMCs and DMRs were found to be distributed more on the X chromosome than on the autosome, and they were covered by gene clusters linked to germ cell formation and development. In conclusion, these findings could enhance our ability to make informed decisions when deciding on superior bulls and advance our understanding of paternal epigenetic inheritance.

Developmental programming of production and reproduction in dairy cows: II. Association of gestational stage of maternal exposure to heat stress with offspring's birth weight, milk yield, reproductive performance and AMH concentration during the first lactation period

Although the negative effect of maternal exposure to heat stress on production and reproduction of offspring has been reported, there are some discrepancies among various studies about which gestational stage is more critical in this regard. Therefore, the present research was conducted to identify during which stage(s) of pregnancy maternal exposure to heat stress would lead to more dramatic decrease in productive and reproductive performance of offspring. To this end, offspring were classified based on the gestational stage they were in utero exposed to heat stress into four categories, including heat stress exposure (HSE) during only the first trimester of gestation (HSE1), HSE during the first and second trimester of gestation (HSE2), HSE during the second and third trimester of gestation (HSE3) and HSE during only the third trimester of gestation (HSE4). In study I, data of birth weight, milk yield and reproductive variables of 11,788 offspring and data of the month they were conceived were retrieved. In study II, blood samples (n = 521) were collected from offspring in various categories of HSE for measurement of serum AMH. Offspring in HSE1 and HSE2 categories were heavier than offspring in HSE3 and HSE4 categories (P < 0.0001). Offspring in HSE1 and HSE3 categories had the lowest and highest milk production, respectively (P < 0.05). First service conception rate was the greatest and worst in HSE1 and HSE4 categories, respectively (P < 0.05). Service per conception and calving to conception interval were greater in HSE2 than HSE4 category (P < 0.05). Concentration of AMH was lower in HSE1 than HSE4 category (P < 0.05). In conclusion, the present study indicated that the early stage of gestation could be a more critical period for the negative impact of in utero heat stress on developmental programming of milk production and ovarian reserves. Yet an evident temporal pattern for the adverse effect of maternal heat stress on developmental programming of reproductive performance in offspring was not found.

Developmental programming of production and reproduction in dairy cows: I. Association of maternal parity with offspring's birth weight, milk yield, reproductive performance and AMH concentration during the first lactation period

Multiparous dams have been reported to produce offspring with greater fertility and higher AMH concentration, as a marker of ovarian reserves, as compared with nulliparous and primiparous dams. Yet it has remained to be addressed whether this phenomenon can still be true for old multiparous cows which might experience some geriatric changes in their reproductive system. Therefore, the present study was conducted to evaluate the productive and reproductive performance of offspring with different maternal parity. To this end, offspring were classified based on their maternal parities into four categories, including offspring of nulliparous (no previous parity), primiparous (one previous parity), young multiparous (two to six previous parities) and old multiparous (seven or more previous parities) dams. In study I, data of birth weight, milk yield and reproductive variables of 11,788 offspring and data of their maternal parity were retrieved. In study II, blood samples (n = 521) were collected from offspring with various maternal parity for measurement of serum AMH. Birth weight was the lowest in the offspring of nulliparous dams (P < 0.0001) and it was lower in offspring of primiparous and old multiparous dams than offspring of young multiparous dams (P < 0.05). Milk production was the lowest in offspring of old multiparous dams (P < 0.01), and it was lower in offspring of young multiparous dams than offspring of nulliparous and primiparous dams (P < 0.0001). Offspring of old multiparous dams had greater first service conception rate, less services per conception and shorter calving to conception interval than offspring of nulliparous, primiparous and young multiparous dams (P < 0.05). Furthermore, AMH concentration was higher in offspring of old multiparous dams than offspring of nulliparous and primiparous dams (P < 0.05). In conclusion, the present study revealed greater milk production in offspring resulting from dams with lower parity, probably due to the genetic selection for improvement of milk production in dairy cows which imparts the younger generations greater genetic merits for milk production. Reproductive performance, however, was greater in offspring born to dams with higher parity, particularly those born to old multiparous dams, and this phenomenon might be related to their lower milk production and higher AMH concentration.

The Role of Reproduction and Genetic Variation in Polish White-Backed Cows in the Breed Restoration Process

Local breeds are the main reservoir of biodiversity of farm animals. According to FAO, they account for 87% of all described breeds in the world. To ensure that they are adequately protected, they should be continually monitored for genetic variation. Another crucial factor is reproduction, which is the most important guarantee of population growth. In the present study, genetic variation in 372 Polish White-Backed cows was determined using DNA microsatellite sequences, taking into account their parentage. Reproductive parameters were analysed as well, based on data from 3658 lactations of 1128 Polish White-Backed cows. The results indicate that despite the small initial population and the implementation of a moderate selection of animals, the existing population of Polish White-Backed cattle has a high level of genetic variation, reflected in the degree of heterozygosity (0.761). Regarding reproductive traits, despite their late age at first calving, Polish White-Backed cows were shown to be distinguished by very good fertility parameters in comparison to other breeds raised in Poland. These findings not only confirm the value of protecting local cattle breeds around the world but may also be of importance in developing selection indices for highly productive breeds, in which reproductive functioning should be one of the most important factors considered.

Effect of reproductive management programs that prioritized artificial insemination at detected estrus or timed artificial insemination on the economic performance of primiparous Holstein cows of different genetic merit for fertility

The objective of this randomized controlled experiment was to evaluate the effect of reproductive management programs that prioritized artificial insemination (AI) at detected estrus (AIE) or timed AI (TAI) during the first lactation on the economic performance of dairy cows of different genomically enhanced predicted transmitting ability for fertility. Lactating primiparous Holstein cows from 6 commercial farms were stratified into high, medium, and low fertility groups based on a reproduction index value calculated from multiple genomically enhanced predicted transmitting abilities to predict the number of days to achieve pregnancy. Within herd and fertility group, cows were randomly assigned either to a program that prioritized AIE (P-AIE; n = 1,416) and used TAI for cows not AIE for all AI services or another that prioritized TAI and had an extended voluntary waiting period for first service and prioritized TAI for second and greater AI services (P-TAI; n = 1,338). Cash flow (CF) per cow accumulated for the experimental (first) and second calving interval (CIN) and cash flow per slot per 28 mo after calving in the experimental lactation were calculated. Market and rearing heifer cost values were used for estimating CF. For cows in the high fertility group, a positive effect of delayed pregnancy on milk income during the first lactation was observed (+$248 for P-TAI) but was insufficient to generate significant differences in CF between treatments mainly because of milk income compensation in the second lactation (+$125 for P-AIE) and minor reductions in reproductive cost and gains in calf value for the P-AIE treatment. In this regard, CF for 2 CIN was greater for the P-TAI treatment by $61 and $86 for market and rearing replacement heifer cost, respectively. Similarly, CF per slot was favorable to the P-TAI treatment but only by $13 and $47 for market and rearing replacement heifer cost, respectively. For cows in the low fertility group, CF was numerically in favor of the P-AIE treatment due to a pregnancy and herd exit dynamics that resulted in gains in milk income over feed cost during the first ($29) and second ($113) lactation. Differences in CF for the 2 CIN were $58 and $47 for market or rearing heifer value, respectively, and $77 and $19 for market and rearing heifer values, respectively for the slot analysis. Differences in CF between cows of different genetic merit for fertility were consistent across treatment and estimation method. Of note, cows in the low fertility group had greater CF than cows in the high fertility group in all comparisons, ranging from $198 per cow for 2 CIN to as much as $427 per slot. For the low fertility group, greater milk production contributed directly (milk income over feed cost) and indirectly (reduced culling) to increased CF. We concluded that genetic merit for fertility and CF are associated because cows of inferior genetic potential for fertility had greater CF than cows of superior genetic for fertility despite some increased costs and reduced revenues. Also, the magnitude of the CF differences observed for cows of different genetic merit for fertility managed with the P-AIE or P-TAI program may be valuable to commercial dairy farms but did not allow to conclusively support the choice of a type of reproductive management strategy for cows of different genetic merit for fertility.

Association of plasma miRNAs with early life performance and aging in dairy cattle

Early life performance traits in dairy cattle can have important influences on lifetime productivity. Poor health and fertility are of great economical and animal welfare concern. Circulating miRNAs have been linked to several livestock traits, including resistance to infection, fertility, and muscle development. This study aimed to identify circulating miRNAs associated with early life performance traits and aging in dairy cattle. Plasma samples from female calves (n = 12) identified retrospectively as differing in health, growth, and fertility outcomes prior to first calving were analyzed using PCR arrays detecting 378 miRNAs. Levels of 6 miRNAs differed significantly in calves with poor growth/fertility relative to controls (t-test: P<0.05). Additionally, general(ized) (non)linear mixed models identified 1 miRNA associated with average daily gain until weaning, 22 with live bodyweight at one year of age, 47 with age at first service, and 19 with number of infections before first calving. Out of 85 distinct miRNAs that were associated with at least one animal trait, 9 miRNAs were validated by RT-qPCR in a larger cohort (n = 91 animals), which included longitudinal plasma samples (calf, heifer, first lactation cow). Significant associations (P<0.05) involving individual miRNAs or ratios between miRNAs and early-life performance traits were identified, but did not retain significance after multiple testing adjustment. However, levels of 8 plasma miRNAs (miR-126-3p, miR-127, miR-142-5p, miR-154b, miR-27b, miR-30c-5p, miR-34a, miR-363) changed significantly with age, most prominently during the calf-to-heifer transition. Comparative RT-qPCR analyses of these miRNAs across 19 calf tissues showed that most were ubiquitously expressed. Online database mining identified several pathways involved in metabolism and cell signaling as putative biological targets of these miRNAs. These results suggest that miR-126-3p, miR-127, miR-142-5p, miR-154b, miR-27b, miR-30c-5p, miR-34a, miR-363 are involved in regulating growth and development from birth to first lactation (~2 years old) and could provide useful biomarkers of aging in cattle.

Review: Genetic mutations affecting bull fertility

Cattle are a well-suited "model organism" to study the genetic underpinnings of variation in male reproductive performance. The adoption of artificial insemination and genomic prediction in many cattle breeds provide access to microarray-derived genotypes and repeated measurements for semen quality and insemination success in several thousand bulls. Similar-sized mapping cohorts with phenotypes for male fertility are not available for most other species precluding powerful association testing. The repeated measurements of the artificial insemination bulls' semen quality enable the differentiation between transient and biologically relevant trait fluctuations, and thus, are an ideal source of phenotypes for variance components estimation and genome-wide association testing. Genome-wide case-control association testing involving bulls with either aberrant sperm quality or low insemination success revealed several causal recessive loss-of-function alleles underpinning monogenic reproductive disorders. These variants are routinely monitored with customised genotyping arrays in the male selection candidates to avoid the use of subfertile or infertile bulls for artificial insemination and natural service. Genome-wide association studies with quantitative measurements of semen quality and insemination success revealed quantitative trait loci for male fertility, but the underlying causal variants remain largely unknown. Moreover, these loci explain only a small part of the heritability of male fertility. Integrating genome-wide association studies with gene expression and other omics data from male reproductive tissues is required for the fine-mapping of candidate causal variants underlying variation in male reproductive performance in cattle.

Validating the female fertility estimated breeding value in Australian commercial dairy herds

We conducted a retrospective cohort study to validate the efficacy of the Australian multitrait fertility estimated breeding value (EBV). We did this by determining its associations with phenotypic measures of reproductive performance (i.e., submission rate, first service conception rate, and early calving). Our secondary aim was to report the associations between these reproductive outcomes and management and climate-related factors hypothesized to affect fertility. Our study population included 38 pasture-based dairy herds from the northern Victorian irrigation region in Australia. We collected records for 86,974 cows with 219,156 lactations and 438,578 mating events from the date on which managers started herd recording until December 2016, comprising both fertility-related data such as insemination records, calving dates, and pregnancy test results, and systems-related data such as production, herd size, and calving pattern. We also collected hourly data from 2004 to 2017 from the closest available weather station to account for climate-related factors (i.e., temperature humidity index; THI). Multilevel Cox proportional hazard models were used to analyze time-to-event outcomes (days to first service, days to cow calving following the planned herd calving start date), and multilevel logistic regression models for binomial outcomes (conception to first service) in the Holstein-Friesian and Jersey breeds. A 1-unit increase in daughter fertility EBV was associated with a 5.4 and 8.2% increase in the daily hazard of calving in the Holstein-Friesian and Jersey breeds respectively. These are relative increases (i.e., a Holstein-Friesian herd with a 60% 6-wk in-calf rate would see an improvement to 63.2% with a 1-unit increase in herd fertility EBV). Similar results were obtained for submission and conception rate. Associations between 120-d milk yield and reproductive outcome were complicated by interactions with 120-d protein percentage and calving age, depending on the breed and outcome. In general, we found that the reproductive performance of high milk-yielding animals deteriorated faster with age than low milk-yielding animals, and high protein percentage exacerbated the differences between low and high milk-yielding animals. Climate-related factors were also associated with fertility, with a 1-unit increase in maximum THI decreasing first service conception rate by 1.2% for Holstein-Friesians but having no statistically significant association in the Jersey breed. However, THI had a negative association in both breeds on the daily hazard of calving. Our study validates the efficacy of the daughter fertility EBV for improving herd reproductive performance and identifies significant associations between 120-d milk and protein yields and THI on the fertility of Australian dairy cows.

The effects of rumen protected methionine supplementation on the performance of primiparous dairy cows using the Presynch-Ovsynch protocol

The purpose of this study was to examine the effects of rumen-protected methionine (RPM) supplementation on the reproductive and productive performance of primiparous dairy cows fed two levels of protein. The Presynch-Ovsynch protocol was used to synchronize 36 lactating Holstein cows that were assigned randomly to one of six dietary treatments: (1) 14% CP and without RPM diet (14CP-0RPM; n = 6), (2) 14% CP and 15 g/head/day RPM (14CP-15RPM; n = 6), (3) 14% CP and 25 g/head/day RPM (14CP-25RPM; n = 6), (4) 16% CP and without RPM diet (16CP-0RPM; n = 6), (5) 16% CP and 15 g/head/day RPM (16CP-15RPM; n = 6), and (6) 16% CP and 25 g/head/day RPM (16CP-25RPM; n = 6). Independent of CP levels, feeding RPM had reduced the calving interval (P < 0.01). Feeding RPM increased (P < 0.01) overall plasma progesterone (P4). Feeding 16CP-15RPM increased (P < 0.01) overall plasma P4. Feeding 16% CP increased (P < 0.01) 4% fat corrected milk, energy corrected milk, milk fat and protein yield, and milk casein. Moreover, feeding the 25RPM has increased (P < 0.01) 4% fat corrected milk, energy corrected milk, milk fat, and protein yield. Compared with other treatments, feeding 16CP-25RPM or 16CP-15RPM enhanced (P < 0.01) milk yield and milk fat yield. In conclusion, feeding 16% CP with RPM boosted the productivity and reduced the calving interval in primiparous lactating dairy cows.

Maternal metabolic health and fertility: we should not only care about but also for the oocyte!

Metabolic disorders due to obesity and unhealthy lifestyle directly alter the oocyte's microenvironment and impact oocyte quality. Oxidative stress and mitochondrial dysfunction play key roles in the pathogenesis. Acute effects on the fully grown oocytes are evident, but early follicular stages are also sensitive to metabolic stress leading to a long-term impact on follicular cells and oocytes. Improving the preconception health is therefore of capital importance but research in animal models has demonstrated that oocyte quality is not fully recovered. In the in vitro fertilisation clinic, maternal metabolic disorders are linked with disappointing assisted reproductive technology results. Embryos derived from metabolically compromised oocytes exhibit persistently high intracellular stress levels due to weak cellular homeostatic mechanisms. The assisted reproductive technology procedures themselves form an extra burden for these defective embryos. Minimising cellular stress during culture using mitochondrial-targeted therapy could rescue compromised embryos in a bovine model. However, translating such applications to human in vitro fertilisation clinics is not simple. It is crucial to consider the sensitive epigenetic programming during early development. Research in humans and relevant animal models should result in preconception care interventions and in vitro strategies not only aiming at improving fertility but also safeguarding offspring health.

Blood Transcriptome Analysis of Beef Cow with Different Parity Revealed Candidate Genes and Gene Networks Regulating the Postpartum Diseases

Maternal parity is an important physiological factor influencing beef cow reproductive performance. However, there are few studies on the influence of different calving periods on early growth and postpartum diseases. Here, we conducted blood transcriptomic analysis on cows of different parities for gene discovery. We used Short Time Series Expression Miner (STEM) analysis to determine gene expression levels in cows of various parities and divided multiple parities into three main periods (nulliparous, primiparous, and multiparous) for subsequent analysis. Furthermore, the top 15,000 genes with the lowest median absolute deviation (MAD) were used to build a co-expression network using weighted correlation network analysis (WGCNA), and six independent modules were identified. Combing with Exon Wide Selection Signature (EWSS) and protein-protein interaction (PPI) analysis revealed that TPCN2, KIF22, MICAL3, RUNX2, PDE4A, TESK2, GPM6A, POLR1A, and KLHL6 involved in early growth and postpartum diseases. The GO and KEGG enrichment showed that the Parathyroid hormone synthesis, secretion, and action pathway and stem cell differentiation function-related pathways were enriched. Collectively, our study revealed candidate genes and gene networks regulating the early growth and postpartum diseases and provided new insights into the potential mechanism of reproduction advantages of different parity selection.

Simultaneous free fatty acid elevations and accelerated desaturation in plasma and oocytes in early postpartum dairy cows under intensive feeding management

A severe negative energy balance and high circulating free fatty acids (FFA) in postpartum cows impair fertility. The lipotoxicity of FFA has been shown to decrease the quality of bovine oocytes in vitro. Therefore, excess FFA in cells is converted to triacylglycerol (TAG), a non-toxic form, to avoid lipotoxicity. We recently reported that the TAG content in oocytes was higher in postpartum lactating cows subjected to grazing management than in heifers (Theriogenology 176: 174-182, 2021). The present study investigated the compositions of the energy metabolism-related lipids, FFA and TAG, in the plasma and oocytes of cows at different lactation stages under indoor intensive feeding management in order to obtain insights into lipotoxicity in oocytes, particularly those in early postpartum cows. Blood and oocytes were collected from 20 lactating cows categorized into the following lactation groups: 20-30 days in milk (DIM) (n = 5), 40-50 DIM (n = 5), 60-80 DIM (n = 5), and 130-160 DIM (n = 5). Daily energy balance data were obtained for 3 weeks prior to oocyte collection using the ovum pick up (OPU) method. The contents and compositions of FFA and TAG in plasma and oocytes were analyzed using liquid chromatography-mass spectrometry. As expected, plasma FFA was high at 20-30 DIM, decreased by 50 DIM, and was maintained at a low level for the remainder of the experimental period. Similar changes were observed in oocyte FFA and TAG with DIM as plasma FFA. Oocyte FFA positively correlated with plasma FFA (P < 0.05), but negatively correlated with the mean energy balance 1 and 21 days before OPU (P < 0.05). Relationships were noted between the composition and content of FFA in plasma and oocytes, with the FFA 16:1/16:0 and 18:1/18:0 ratios positively correlating with the total amount of FFA (P < 0.05). Elevated oocyte FFA in cows in the early postpartum period under intensive feeding management suggested that oocytes were at a high risk of FFA lipotoxicity. Furthermore, the present results implied that the severe negative energy balance in the previous few weeks was closely related to increases in oocyte FFA, which supports the importance of long-term cow feeding management for preserving the quality of oocytes in the early postpartum period. The present results provide insights into the effects of high circulating FFA on the fertility of postpartum cows.

Reproductive tract size and position score: Estimation of genetic parameters for a novel fertility trait in dairy cows

The dairy industry is moving toward selecting animals with better fertility to decrease the economic losses linked to reproductive issues. The reproductive tract size and position score (SPS) was recently developed in physiological studies as an indicator of pregnancy rate and the number of services to conception. Cows are scored as SPS 1, 2, or 3 based on the size of their reproductive tract and its position in the pelvis, as determined by transrectal palpation. The objective of this study was to estimate genetic parameters for SPS to assess its potential as a novel fertility trait. Phenotypes were collected at the University of British Columbia's research herd from 2017 to 2020, consisting of 3,247 within- and across-lactation SPS records from 490 Holstein cows. A univariate animal model was used to estimate the variance components for SPS. Both threshold and linear models were fit under a Bayesian approach and the results were compared using the Spearman rank correlation (r) between the estimated breeding values. The 2 models ranked the animals very similarly (r = 0.99), and the linear model was selected for further analysis. Genetic correlations with other currently evaluated traits were estimated using a bivariate animal model. The posterior means (± posterior standard deviation) for heritability and repeatability within- and across-lactation were 0.113 (± 0.013), 0.242 (± 0.012), and 0.134 (± 0.014), respectively. The SPS showed null correlations with production traits and favorable correlations with traditional fertility traits, varying from -0.730 (nonreturn rate) to 0.931 (number of services). Although preliminary, these results are encouraging because SPS seems to be more heritable than and strongly genetically correlated with number of services, nonreturn rate, and first service to conception, indicating potential for effective indirect selection response on these traits from SPS genetic selection. Therefore, further studies with larger data sets to validate these findings are warranted.

Associations between anogenital distance and measures of fertility in lactating North American Holstein cows: A validation study

Anogenital distance (AGD) has been defined in dairy cows as the distance from the center of the anus to the base of the clitoris. Initial reports on nulliparous Holstein heifers and first- and second-parity Holstein cows have found inverse relationships between AGD and measures of fertility. Our primary objective was to determine the relationship between AGD and measures of fertility in a larger population of North American Holstein cows to validate our previous finding that AGD is inversely related to fertility. Secondary objectives were to determine the associations between AGD and parity, and milk yield. Using digital calipers, we measured AGD in 4,709 Holstein cows [mean ± standard deviation (SD); parity 2.3 ± 1.4; days in milk (DIM) 154 ± 94; 305-d mature equivalent (ME) milk yield 13,759 ± 2,188 kg] from 18 herds in Western Canada and 1 herd in the USA. Anogenital distance (mm) was normally distributed with a mean (±SD) of 132 ± 12, ranging from 95 to 177, and a median of 133. Anogenital distance was linearly but inversely associated with pregnancy to first artificial insemination (P/AI1). For every 1-mm increase in AGD, the estimated probability of P/AI1 decreased by 0.8%. The optimum AGD cut-point that predicted probability of P/AI1 with sensitivity and specificity of 45 and 55%, respectively, was 129 mm. Consequently, data were categorized into either short (≤129) or long (>129) AGD groups across parities, and associations between AGD, parity (first, second, and third+), and fertility measures were determined. Rates of P/AI1 were greater (36 vs. 30%) in short- than in long-AGD cows; short-AGD cows required fewer AI per conception (2.3 vs. 2.4) and had fewer days open (137 vs. 142), and a greater proportion of short-AGD cows (67 vs. 64%) was pregnant by 150 DIM compared with long-AGD cows. The rates of pregnancy up to 150 (hazard ratio of 0.91) and 250 DIM (hazard ratio of 0.93) were smaller in long- than in short-AGD cows. Anogenital distance had a weak positive association with both parity (r = 0.22) and 305-d ME milk yield (r = 0.04). Results indicate an inverse relationship between AGD and measures of fertility in lactating cows, validating our earlier report. We infer that although selecting cows for short AGD is expected to have an adverse effect on milk yield, the anticipated gain in fertility will outweigh the small decline in milk yield, strengthening the potential of AGD as a novel reproductive phenotype for use in future breeding programs to improve fertility.

Symposium review: Use of multiple biological, management, and performance data for the design of targeted reproductive management strategies for dairy cows

As the reproductive efficiency of dairy cattle continues to improve in response to better management and use of technology, novel reproductive management approaches will be required to improve herd performance, profitability, and sustainability. A potential approach currently being explored is targeted reproductive management. This approach consists of identifying cows with different reproductive and performance potential using multiple traditional and novel sources of biological, management, and performance data. Once subgroups of cows that share biological and performance features are identified, reproductive management strategies specifically designed to optimize cow performance, herd profitability, or alternative outcomes of interest are implemented on different subgroups of cows. Tailoring reproductive management to subgroups of cows is expected to generate greater gains in outcomes of interest than if the whole herd is under similar management. Major steps in the development and implementation of targeted reproductive management programs for dairy cattle include identification and validation of robust predictors of reproductive outcomes and cow performance, and the development and on-farm evaluation of reproductive management strategies for optimizing outcomes of interest for subgroups of cows. Predictors of cow performance currently explored for use in targeted management include genomic predictions; behavioral, physiological, and performance parameters monitored by sensor technologies; and individual cow and herd performance records. Once the most valuable predictive sources of variation are identified and their effects quantified, novel analytic methods (e.g., machine learning) for prediction will likely be required. These tools must identify groups of cows for targeted management in real time and with no human input. Despite some encouraging research evidence supporting the development of targeted reproductive management strategies, extensive work is required before widespread implementation by commercial farms.

Are subjectively scored linear type traits suitable predictors of the genetic merit for feed intake in grazing Holstein-Friesian dairy cows?

Measuring dry matter intake (DMI) in grazing dairy cows using currently available techniques is invasive, time consuming, and expensive. An alternative to directly measuring DMI for use in genetic evaluations is to identify a set of readily available animal features that can be used in a multitrait genetic evaluation for DMI. The objectives of the present study were thus to estimate the genetic correlations between readily available body-related linear type traits and DMI in grazing lactating Holstein-Friesian cows, but importantly also estimate the partial genetic correlations between these linear traits and DMI, after adjusting for differences in genetic merit for body weight. Also of interest was whether the predictive ability derived from the estimated genetic correlations materialized upon validation. After edits, a total of 8,055 test-day records of DMI, body weight, and milk yield from 1,331 Holstein-Friesian cows were available, as were chest width, body depth, and stature from 47,141 first lactation Holstein-Friesian cows. In addition to considering the routinely recorded linear type traits individually, novel composite traits were defined as the product of the linear type traits as an approximation of rumen volume. All linear type traits were moderately heritable, with heritability estimates ranging from 0.27 (standard error = 0.14) to 0.49 (standard error = 0.15); furthermore, all linear type traits were genetically correlated (0.29 to 0.63, standard error 0.14 to 0.12) with DMI. The genetic correlations between the individual linear type traits and DMI, when adjusted for genetic differences in body weight, varied from -0.51 (stature) to 0.48 (chest width). These genetic correlations between DMI and linear type traits suggest linear type traits may be useful predictors of DMI, even when body weight information is available. Nonetheless, estimated genetic merit of DMI derived from a multitrait genetic evaluation of linear type traits did not correlate strongly with actual DMI in a set of validation animals; the benefit was even less if body weight data were also available.

Cellular Stress Responses in Oocytes: Molecular Changes and Clinical Implications

The oocyte may be exposed to several sources of stress during its growth and maturation, which may lead to reduced fertility. Unfolded protein responses (UPRs) play a central role to maintain cell survival and repair. Transcription of heat shock proteins (HSPs) is a key element to facilitate reestablishment of cellular homeostasis. Unlike somatic cells, cellular mechanisms by which oocytes can sense and respond to stress are not well described. In here, we provide an overview about the impact of cellular stress, particularly due to lipotoxicity, oxidative stress, and heat stress on oocyte developmental competence. Next, we focus on the expression of HSPs in oocytes and their potential role in UPRs in oocytes and embryos. This is based on a comprehensive shotgun proteomic analysis of mature bovine oocytes performed in our laboratory, as well as a literature review. The topic is discussed in light of our understanding of similar mechanisms in other cell types and the limited transcriptional activity in oocytes. More fundamental research is needed both at the transcriptomic and proteomic levels to further understand cell stress response mechanisms in oocytes and early developing embryos, their critical interactions, and their long-term effects. Strategies to provide targeted external support to prevent or reduce cell stress levels during oocyte maturation or early embryo development under maternal metabolic stress conditions should be developed to maximize the odds of producing good quality embryos and guarantee optimal viability.

A statistical evaluation of associations between reproductive performance and milk composition and animal factors on grazing dairy cows in two New Zealand dairy farms

AIMS

To determine if milk composition, milk yield, live weight, live weight change, breed and heterosis are associated with reproductive performance in dairy cows from two dairy farms under New Zealand grazing conditions.

METHODS

Milk composition was determined in herd tests from 205 Holstein-Friesian (F), 77 Jersey (J) and 351 F × J crossbred cows from two Massey University dairy herds in the 2016 and 2017 production seasons. Mating occurred from October to December in each production season. The start of breeding to first service (SBFS), start of breeding to conception (SBCO), submission rate at 21 days (SR21), pregnancy rate at 21 (PR21) and 42 days (PR42) were calculated for each cow. These traits were analysed using mixed linear models that included fixed effects for herd, production season, regression coefficients of deviation from median calving date, lactation number, proportion of F, F × J heterosis, energy-corrected milk yield (ECMY), percentages of fat, protein and lactose, milk urea nitrogen (MUN), live weight and change in live weight, with random effects for cow and residual error. The variables with binomial distribution were analysed using logistic regression.

RESULTS

Deviation from the herd's median calving date had a significant effect (p < 0.05) on all reproductive traits. Proportion of F was significant (p = 0.022) on PR21, and F × J heterosis effects were significant on PR21 (p = 0.049) and PR42 (p = 0.046). F cows had 17.8% higher PR21 than J cows, and F × J cows had higher reproductive performance than the mean of the two purebreeds. ECMY was negatively associated with SBFS (p = 0.001) and SBCO (p = 0.001) and positively associated with PR21 (p = 0.002) and PR42 (p = 0.001). Protein percentage was positively associated (p < 0.05) with PR21 and PR42, whereas lactose percentage was negatively associated (p < 0.05) with PR21 and PR42. Cows gaining live weight were more likely to become pregnant within 21 days of the start of breeding (p = 0.020). Milk urea nitrogen was negatively associated (p = 0.042) with SR21.

CONCLUSIONS AND CLINICAL RELEVANCE

This study confirms that breed, heterosis, ECMY, protein and lactose percentages, live weight change and calving date are associated with the reproductive performance of grazing cows. Results from this study contrast with the historical antagonism between milk production and reproductive performance in dairy cattle, demonstrating that well managed cows can achieve high levels of production and good reproductive performance. MUN was not associated with reproductive performance traits, except with SR21.

Postpartum cows showed high oocyte triacylglycerols concurrently with high plasma free fatty acids

Impaired oocyte quality is one of the main causes of low fertility in modern high-yielding dairy cows. One of the potential factors of the impaired oocyte quality is the effects of free fatty acids (FFA). In fact, high FFA supplementation to culture media exacerbated oocyte developmental competence in vitro. Meanwhile, artificially induced high blood FFA levels in heifers did not affect the lipid composition of oocytes in vivo; however, the oocyte lipid profile of postpartum cows has not yet been investigated. Therefore, the profile of lipids involved in energy metabolism, including FFA and triacylglycerols (TAG), and their relationship between plasma and oocytes were compared among cows at different lactation stages. Heifers were used as a control group that was not affected by lactation. Plasma and oocytes were collected from heifers (n = 4) and 14 Holstein cows categorized to the early lactation stage: 25-47 days in milk (DIM) (n = 6), peak lactation stage: 61-65 DIM (n = 4), and middle lactation stage: 160-202 DIM (n = 4). The FFA and TAG profiles of plasma and oocytes were examined by liquid chromatography mass spectrometry. Plasma FFA positively correlated with oocyte TAG (P < 0.05). Plasma FFA and oocyte TAG were significantly higher in cows in the early lactation stage than in heifers (P < 0.05), while the peak and middle lactation stage groups had intermediate levels. The proportion of oleic acid in plasma increased concurrently with elevations in total FFA, while the compositions of oocyte FFA and TAG fatty acyls were constant regardless of plasma FFA concentration or oocyte TAG content. The present results suggest that high postpartum plasma FFA concentrations affect the quantity of oocyte TAG. Taken together with the adverse effects of high FFA concentrations on oocyte developmental competence in vitro, oocyte quality in postpartum cows may be impaired due to high circulating FFA concentrations. These results provide a more detailed understanding of the effects of postpartum high circulating FFA concentrations on the low fertility of cows.

Invited review: Use of assisted reproduction techniques to accelerate genetic gain and increase value of beef production in dairy herds

The contribution of the calf enterprise to the profit of the dairy farm is generally considered small, with beef bull selection on dairy farms often not considered a high priority. However, this is likely to change in the future as the rapid rate of expansion of the dairy herd in some countries is set to plateau and improvements in dairy herd fertility combine to reduce the proportion of dairy breed calves required on dairy farms. This presents the opportunity to increase the proportion of beef breed calves born, increasing both the value of calf sales and the marketability of the calves. Beef embryos could become a new breeding tool for dairies as producers need to reassess their breeding policy as a consequence of welfare concerns and poor calf prices. Assisted reproductive technologies can contribute to accelerated genetic gain by allowing an increased number of offspring to be produced from genetically elite dams. There are the following 3 general classes of donor females of interest to an integrated dairy-beef system: (1) elite dairy dams, from which oocytes are recovered from live females using ovum pick-up and fertilized in vitro with semen from elite dairy bulls; (2) elite beef dams, where the oocytes are recovered from live females using ovum pick-up and fertilized with semen from elite beef bulls; and (3) commercial beef dams (≥50% beef genetics), where ovaries are collected from the abattoir postslaughter, and oocytes are fertilized with semen from elite beef bulls that are suitable for use on dairy cows (resulting embryo with ≥75% beef genetics). The expected benefits of these collective developments include accelerated genetic gain for milk and beef production in addition to transformation of the dairy herd calf crop to a combination of good genetic merit dairy female calves and premium-quality beef calves. The aim of this review is to describe how these technologies can be harnessed to intensively select for genetic improvement in both dairy breed and beef breed bulls suitable for use in the dairy herd.

Moving towards sustainable breeding objectives and cow welfare in dairy production: a South African perspective

Genetic advancements have resulted in improved dairy production over many decades, due to the focus of breeding objectives on production as the driving force for genetic progress and overall farm profitability. Major advancements were made in the easy-to-measure traits with moderate to high heritability, which resulted in unintended consequences on herd fertility, health, and welfare of cows. In addition, climate change and animal welfare concerns demanded balanced breeding objectives and selection approaches for sustainable production-including health and longevity. The inclusion of genomic information into genetic evaluations has been proved to benefit traits associated with welfare and sustainable production. Cow welfare traits remain complex and suitable phenotypes are not always easy to measure or readily available for genetic evaluations. The challenge for improvement of cow welfare often lies within implementation of sensitive and measurable parameters. The aim of this review was to explore the reconsideration of breeding objectives in the dairy industry towards sustainable dairy production and cow welfare with reference to selection of dairy animals in South Africa.

Effect of flunixin meglumine treatment during and after embryo transfer on the pregnancy rate in cattle

This study aimed to determine the effect of flunixin meglumine treatment during and after the transfer of in vivo produced embryos to Angus (cows) and Holstein (cows and heifers) breeds of cattle on pregnancy rate. Holstein cows were used as donors in the study. A double dose of prostaglandin F2α was administered to the recipient animals for synchronization. Uterine flushing was performed in donors on day 7 after artificial insemination. A total of 295 transferable embryos were obtained. These embryos were transferred to Angus cows (n = 85), Holstein heifers (n = 80) and Holstein cows (n = 130). After the transfer, these animals were divided into three subgroups. The first subgroup (TI) was administered flunixin meglumine during embryo transfer, and the second subgroup (TII) was administered flunixin meglumine both during embryo transfer and on days 8 and 9 after the transfer. The third subgroup (TIII) was not administered anything and it was considered the control group. Pregnancy examination of the recipients was performed on days 30-35 after the transfer using real-time ultrasonography. The pregnancy rates after embryo transfer were found to be 43.52% in Angus cows, 42.5% in Holstein heifers, and 24.61% in Holstein cows (p < .05). When the animals were not classified according to breed, the pregnancy rates in subgroups TI, TII and TIII were found to be 29.29%, 45.10% and 29.79%, respectively (p < .05). In addition, the pregnancy rates were higher in TII and TIII subgroups of Angus cows and Holstein heifers compared to that of Holstein cows (p < .05). As a result, the pregnancy rates obtained after embryo transfer in Angus cows and Holstein heifers were found to be higher than that in Holstein cows. In addition, it was concluded that the administration of flunixin meglumine during and during/after embryo transfer has a positive effect on pregnancy rates in Angus cows and Holstein heifers.

Contribution of herd characteristics to best linear unbiased estimates of slaughter traits in beef cattle

Genetic evaluations separate phenotypes into their contributing additive genetic effects and non-(additive) genetic effects, with the former termed best linear unbiased predictions, and the latter termed best linear unbiased estimates (BLUEs). For the purpose of the present study, genetic evaluations, along with phenotypic data from 4 137 376 animals, were used to generate herd, year of slaughter and sex contemporary group BLUEs for various slaughter-related traits. These slaughter traits included carcass weight (CW), carcass conformation (CC) and carcass fat (CF). For the 4 665 herds that were consistently slaughtering ≥10 animals/year between the years 2014 and 2018, inclusive, all relevant contemporary group BLUEs were collapsed into a single herd-year value; results herein relate to these herds. The within-year herd-year BLUE correlations between CW and CC, between CW and CF, and between CC and CF were 0.51, 0.10 and -0.04, respectively. The repeatability across years of the herd-year BLUEs for CW, CC and CF was 0.66, 0.59 and 0.50, respectively. Furthermore, when the herds were stratified, within year, on the percentile rank of their herd-year BLUEs, herds had the greatest probability of remaining in the same BLUE stratum from one year to the next. In addition, results from the present study determined that various herd characteristics are associated with differences in the herd BLUEs. Results from the present study could be used to advise beef producers on the most promising strategy to improve the carcass merit of their animals.

Review: Genetic selection of high-yielding dairy cattle toward sustainable farming systems in a rapidly changing world

The massive improvement in food production, as a result of effective genetic selection combined with advancements in farming practices, has been one of the greatest achievements of modern agriculture. For instance, the dairy cattle industry has more than doubled milk production over the past five decades, while the total number of cows has been reduced dramatically. This was achieved mainly through the intensification of production systems, direct genetic selection for milk yield and a limited number of related traits, and the use of modern technologies (e.g., artificial insemination and genomic selection). Despite the great betterment in production efficiency, strong drawbacks have occurred along the way. First, across-breed genetic diversity reduced dramatically, with the worldwide use of few common dairy breeds, as well as a substantial reduction in within-breed genetic diversity. Intensive selection for milk yield has also resulted in unfavorable genetic responses for traits related to fertility, health, longevity, and environmental sensitivity. Moving forward, the dairy industry needs to continue refining the current selection indexes and breeding goals to put greater emphasis on traits related to animal welfare, health, longevity, environmental efficiency (e.g., methane emission and feed efficiency), and overall resilience. This needs to be done through the definition of criteria (traits) that (a) represent well the biological mechanisms underlying the respective phenotypes, (b) are heritable, and (c) can be cost-effectively measured in a large number of animals and as early in life as possible. The long-term sustainability of the dairy cattle industry will also require diversification of production systems, with greater investments in the development of genetic resources that are resilient to perturbations occurring in specific farming systems with lesser control over the environment (e.g., organic, agroecological, and pasture-based, mountain-grazing farming systems). The conservation, genetic improvement, and use of local breeds should be integrated into the modern dairy cattle industry and greater care should be taken to avoid further genetic diversity losses in dairy cattle populations. In this review, we acknowledge the genetic progress achieved in high-yielding dairy cattle, closely related to dairy farm intensification, that reaches its limits. We discuss key points that need to be addressed toward the development of a robust and long-term sustainable dairy industry that maximize animal welfare (fundamental needs of individual animals and positive welfare) and productive efficiency, while also minimizing the environmental footprint, inputs required, and sensitivity to external factors.

Estimated genetic parameters for all genetically evaluated traits in Canadian Holsteins

Genetic improvement is a crucial tool to deal with the increasing demand for high quality, sustainably produced dairy. Breeding programs are based on genetic parameters, such as heritability and genetic correlations, for economically important traits in a population. In this study, we estimated population genetic parameters and genetic trends for 67 traits evaluated on heifers and first-lactation Canadian Holstein cows. The data consisted of approximately 500,000 records with pedigree information collected from 1980 to 2019. Genetic parameters were estimated using bivariate linear animal models under a Bayesian approach. Analyses for the 67 traits resulted in 2,211 bivariate combinations, from which the estimated genetic parameters are reported here. The most highly heritable traits were fat percent (0.66) and protein percent (0.69), followed by stature (0.47). Lowest heritabilities (0.01) were observed for disease-related traits, such as lameness and toe ulcer, and calf survival. The genetic correlations between gestation length, calf size, and calving ease measured on both heifer and cows were close to unity. On the other hand, traits such as body condition score and pin width, cystic ovaries and sole ulcer, rear teat placement, and toe ulcer were genetically unrelated. This study reports genetic parameters that have not been previously published for Canadian Holstein cows, and provides updates of those previously estimated. These estimates are useful for building new indexes, updating existing selection indexes, and for predicting correlated responses due to inclusion of novel traits in the breeding programs.

Exosomal Cargo May Hold the Key to Improving Reproductive Outcomes in Dairy Cows

The reproductive status of dairy cows remains a challenge for dairy farmers worldwide, with impaired fertility linked to a significant reduction in herd profitability, due in part to impaired immunity, increased metabolic pressure, and longer postpartum anestrous interval (PPAI). Exosomes are nanovesicles released from a variety of cell types and end up in circulation, and carry proteins, bioactive peptides, lipids, and nucleic acids specific to the place of origin. As such, their role in health and disease has been investigated in humans and animals. This review discusses research into exosomes in the context of reproduction in dairy herds and introduces recent advances in mass-spectrometry (MS) based proteomics that have a potential to advance quantitative profiling of exosomal protein cargo in a search for early biomarkers of cattle fertility.

Carcass and efficiency metrics of beef cattle differ by whether the calf was born in a dairy or a beef herd

Beef originates from the progeny of either dairy or beef dams. The objective of the present study was to identify contributing factors to the differences in the carcass merit of progeny from both dam types. This goal was achieved using slaughter records from 16,414 bucket-reared dairy animals (DXD), 5,407 bucket-reared dairy-beef animals (BXD), 42,102 suckle-reared animals from a beef × dairy F1 cross dam (BXF1), and 93,737 suckle-reared animals from a beef × beef cow (BXB). Linear mixed models were used to quantify the least squares means for carcass characteristics in the various progeny genotypes. Nuisance fixed effects adjusted for in the models were: animal heterosis and recombination loss, dam parity, age at slaughter, and contemporary group; age at slaughter was replaced as an independent variable with both carcass weight and carcass fat score where the dependent variable was age at slaughter. In a follow-up analysis, models were re-analyzed where the genetic merit of the sire was adjusted for; a further analysis set the genetic merit of the dam for the dependent variable to be identical for both the dairy and beef dams. The final analysis adjusted to a common sire and dam genetic merit facilitating the estimation of just differences in early-life rearing strategies. Irrespective of the genetic merit of the sire and dam, animals originating from beef herds had heavier and more conformed carcasses. BXB animals had a 67 kg heavier carcass, with a conformation score (scale 1 [poor] to 15 [excellent]) of 5 units greater compared with DXD animals. When the genetic merit of all dams was set to be equal, BXB animals were heavier and better conformed than BXD animals. When the genetic merit for both the sire and dam were set to be equal, carcasses of the BXB animals were 15 kg heavier, with a 0.69 unit superior conformation score compared with the DXD animals; this difference is due to early life experiences. In conclusion, the majority of the inferiority in carcass metrics of calves from dairy herds compared with beef herds is due to differences in the genetic merit of the parents. Nevertheless, even after adjusting the parents to the same genetic merit, progeny from dairy herds were still inferior to their contemporaries born in beef herds, due most likely to the persistence of early life experiences.

Monitoring and Improving the Metabolic Health of Dairy Cows during the Transition Period

Simple Summary

The transition from late gestation to early lactation is a challenging period for dairy cows. A successful transition period depends on metabolic adaptation to the new physiological state in early lactation and proper management in order to support the cow’s requirements. This review paper will discuss various aspects of routine and consistent approaches to collect and analyze herd records, to detect unintended disruptions in performance. In addition, we discuss how to incorporate methods to assess health, production, nutrition, and welfare information to monitor cows during the transition period. Lastly, we discuss management strategies that can be implemented to improve the metabolic health and performance of transition dairy cows.

Abstract

The peripartum period of a dairy cow is characterized by several physiological and behavioral changes in response to a rapid increase in nutrient demands, to support the final stages of fetal growth and the production of colostrum and milk. Traditionally, the transition period is defined as the period 3 weeks before and 3 weeks after parturition. However, several researchers have argued that the transition period begins at the time of dry-off (~60–50 days prior to calving) and extends beyond the first month post-calving in high producing dairy cows. Independent of the definition used, adequate adaptation to the physiological demands of this period is paramount for a successful lactation. Nonetheless, not all cows are successful in transitioning from late gestation to early lactation, leading to approximately one third of dairy cows having at least one clinical disease (metabolic and/or infectious) and more than half of the cows having at least one subclinical case of disease within the first 90 days of lactation. Thus, monitoring dairy cows during this period is essential to detect early disease signs, diagnose clinical and subclinical diseases, and initiate targeted health management to avoid health and production impairment. In this review, we discuss different strategies to monitor dairy cows to detected unintended disruptions in performance and management strategies that can be implemented to improve the metabolic health and performance of dairy cows during the transition period.

Genome-wide association studies for sperm traits in Assaf sheep breed

Sperm quality traits routinely collected by artificial insemination (AI) center for rams progeny test are related with the capacity to produce sperm doses for AI and, in more or less grade, with males' fertility. Low-quality ejaculates are unuseful to perform AI sperm doses, which suppose high economic loses for the AI center. Moreover, sperm quality traits have low heritability values which make traditional genetic selection little efficient to its improvement. In this work, a genome-wide association study (GWAS) was conducted by using sperm quality traits data and 50 K Affymetrix custom chip genotypes of 429 rams of Assaf breed from OVIGEN AI centre. Furthermore, 47 of these rams were also genotyped with the Illumina HD Ovine BeadChip, and therefore HD genotypes were imputed for all rams with phenotype data. Previous to the GWAS, a linear regression model was fitted including sperm traits as dependent variables; the flock of origin, date of sperm collection, and jump number as fixed effects; rams age at collection in months as covariate; and ram permanent effect as random. Pseudo-phenotypes obtained from this model were used as input for GWAS. Associations at the chromosome-wise level (FDR 10%) of 76 single-nucleotide polymorphisms (SNPs) in 4 chromosomes for ejaculate concentration (CON), 20 SNPs in 3 chromosomes for ejaculate volume (VOL), 32 SNPs in 1 chromosome for ejaculate number of spermatozoa (SPZ), and 23 SNPs for spermatozoa mass motility (MOT) in 17 chromosomes were found. Only SNPs associated with MOT overcame the genome-wide significance level. Some candidate genes for sperm traits variability were SLC9C1 (OAR1), TSN (OAR2), and FUT10 (OAR26) for MOT;. DOCK2, CPLANE1, SPEF2, and RAI14 (OAR16) for CON; SCAPER and PSMA4 (OAR18) for VOL; and PARM1 and LOC101110593 (OAR6) for SPZ. SNPs associated with sperm traits were not found to be correlated with milk production genetic variation; however, the high frequencies of some SNPs with negative effect over sperm traits found in animals at the top milk yield estimated breeding values (EBVs) ranking would allow to exert some selective presure to improve rams sperm performances. Effects and frequencies of some of the SNPs detected over sperm quality traits make these variants good candidates to be used in marker-assisted selection to improve sperm characteristics of Assaf rams and AI center efficiency to produce sperm doses.

Analysis of single nucleotide polymorphisms related to heifer fertility in Hanwoo (Korean cattle)

Genome-wide association studies (GWAS) have accelerated the identification of functional trait loci in cattle and identified single nucleotide polymorphisms (SNPs) in candidate genes associated with fertility and production traits in high milk yield dairy cattle. The fertility of Hanwoo (Korean native beef cattle) has declined after the adaptation of a selection program for high quantity and quality meat. However, there are few GWAS studies of fertility in beef cattle. We performed a genome-wide association study of 40 Korean native beef cattle heifers with imputed 770 K genotype and identified 12 significant SNPs within seven regions on three chromosomes (BTA 8, BTA 16 and BTA 24) associated with services per conception (SPC). Five SNPs were located in the ABCA1, BRINP3 and ESRRG genes, which are involved in early embryo development. In addition, 27 proximal genes were identified within 1 Mb of the candidate SNPs, which are involved in muscle cell differentiation and muscle structure development. However, we did not find any previously reported SNPs related to fertility in Holstein cows. Taken together, we identified SNPs associated with SPC and their proximal genes using gene-based analysis and the candidates were different from SNPs associated with subfertility of dairy cattle.

Glyphosate-based herbicide formulations and reproductive toxicity in animals

The adoption of genetically engineered (GE) crops in agriculture has increased dramatically over the last few decades. Among the transgenic plants, those tolerant to the herbicide glyphosate are among the most common. Weed resistance to glyphosate-based herbicides (GBHs) has been on the rise, leading to increased herbicide applications. This, in turn, has led to increased glyphosate residues in feed. Although glyphosate has been considered to be generally safe to animal health, recent studies have shown that GBHs have potential to cause adverse effects in animal reproduction, including disruption of key regulatory enzymes in androgen synthesis, alteration of serum levels of estrogen and testosterone, damage to reproductive tissues and impairment of gametogenesis. This review emphasizes known effects of GBHs on reproductive health as well as the potential risk GBH residues pose to animal agriculture.

Cellular uptake of polymeric nanoparticles by bovine cumulus-oocyte complexes and their effect on in vitro developmental competence

Polymeric nanoparticles (NPs) are produced using bio-compatible and bio-degradable materials such as PLGA (Poly(lactic-co-glycolic acid)). This technology provides a valuable tool to deliver molecules to the subcellular level with a relatively low risk of cytotoxicity. However their use in the field of reproductive biotechnology is not yet scientifically substantiated. The aim of the present study was to test if PLGA NPs can be taken-up by cumulus-enclosed oocytes as a first step towards potential oocyte-targeted applications to enhance oocyte quality and fertility. We conducted a series of experiments using bovine in vitro oocyte maturation as a model to study FITC-conjugated PLGA internalization (using laser-scanning confocal microscopy) and the effect of some important physical (particle size) and chemical (conjugation with PEG) modifications. We show evidence that PLGA NPs can be taken-up by cumulus cells and to a less extent by the enclosed oocytes regardless of the NP size. The NP transfer to the oocyte appear to be transcellular (via cumulus cells and transzonal projections) and paracellular (via zona pellucida). The PLGA NPs were detected in the vicinity of the oocyte as quick as 2 h post-exposure in a protein-free medium and did not compromise cumulus cell viability nor subsequent early embryo development or embryo quality. These results suggest that PLGA NPs may have promising applications as carriers for drug or molecule delivery targeting cumulus cells and oocytes.

Population demographic history and population structure for Pakistani Nili-Ravi breeding bulls based on SNP genotyping to identify genomic regions associated with male effects for milk yield and body weight

The domestic Nili-Ravi water buffalo (Bubalus bubalis) is the best dairy animal contributing 68% to total milk production in Pakistan. In this study, we identified genome-wide single nucleotide polymorphisms (SNPs) to estimate various population genetic parameters such as diversity, pairwise population differentiation, linkage disequilibrium (LD) distribution and for genome-wide association study for milk yield and body weight traits in the Nili-Ravi dairy bulls that they may pass on to their daughters who are retained for milking purposes. The genotyping by sequencing approach revealed 13,039 reference genome-anchored SNPs with minor allele frequency of 0.05 among 167 buffalos. Population structure analysis revealed that the bulls were grouped into two clusters (K = 2), which indicates the presence of two different lineages in the Pakistani Nili-Ravi water buffalo population, and we showed the extent of admixture of these two lineages in our bull collection. LD analysis revealed 4169 significant SNP associations, with an average LD decay of 90 kb for these buffalo genome. Genome-wide association study involved a multi-locus mixed linear model for milk yield and body weight to identify genome-wide male effects. Our study further illustrates the utility of the genotyping by sequencing approach for identifying genomic regions to uncover additional demographic complexity and to improve the complex dairy traits of the Pakistani Nili-Ravi water buffalo population that would provide the lot of economic benefits to dairy industry.

Validation of a beef cattle maternal breeding objective based on a cross-sectional analysis of a large national cattle database

Despite the importance of validating any technology prior to recommendation for use, few studies exist in the scientific literature which have demonstrated the superior performance of high-ranking animals in a given total merit index; this is especially true for maternal cattle selection indexes. The objective of the present study was to demonstrate the impact of the Irish total merit maternal-based index and provide the benefits of using the Irish total merit maternal-based beef index as part of a breeding policy. The validation exercise was undertaken using 269,407 records (which included the cow's own records and her progeny records) from 92,300 females differing in a total merit index for maternal value; a comparison was also made with the Irish terminal index. Association analyses were undertaken within the framework of linear and threshold mixed models; the traits analyzed were fertility (e.g., calving interval), slaughter (e.g., harvest weight), live weight (e.g., weaning weight), and producer-recorded traits (e.g., docility). All traits were analyzed with the maternal index and terminal index fitted as covariate(s) separately. Depending on the independent variable analyzed, the other fixed effects included: parity of cow, heterosis and recombination loss of cow and/or progeny, gender of progeny, and the estimated breeding value of the sire; contemporary group was included as a random effect. The results demonstrate the effectiveness of using total merit indexes to improve performance in a whole range of different traits, despite the often antagonistic genetic correlations among traits that underpin the index. Cows excelling on the maternal index had less calving difficulty, superior fertility performance, lighter carcasses, and live weight, as well as being more easily managed. Additionally, progeny of higher maternal index cows were lighter at birth and more docile albeit with a small impact on slaughter traits. In contrast, higher terminal index cows had more calving difficulty, compromised fertility and had heavier carcasses themselves as well as their progeny. While the differences in phenotypic performance between groups on maternal index was, in most instances, relatively small, the benefits are: (1) expected to be greater when more genetically extreme groups of animals are evaluated and (2) expected to accumulate over time given the cumulative and permanent properties of breeding schemes.

Weighted Gene Correlation Network Meta-Analysis Reveals Functional Candidate Genes Associated with High- and Sub-Fertile Reproductive Performance in Beef Cattle

Improved reproductive efficiency could lead to economic benefits for the beef industry, once the intensive selection pressure has led to a decreased fertility. However, several factors limit our understanding of fertility traits, including genetic differences between populations and statistical limitations. In the present study, the RNA-sequencing data from uterine samples of high-fertile (HF) and sub-fertile (SF) animals was integrated using co-expression network meta-analysis, weighted gene correlation network analysis, identification of upstream regulators, variant calling, and network topology approaches. Using this pipeline, top hub-genes harboring fixed variants (HF × SF) were identified in differentially co-expressed gene modules (DcoExp). The functional prioritization analysis identified the genes with highest potential to be key-regulators of the DcoExp modules between HF and SF animals. Consequently, 32 functional candidate genes (10 upstream regulators and 22 top hub-genes of DcoExp modules) were identified. These genes were associated with the regulation of relevant biological processes for fertility, such as embryonic development, germ cell proliferation, and ovarian hormone regulation. Additionally, 100 candidate variants (single nucleotide polymorphisms (SNPs) and insertions and deletions (INDELs)) were identified within those genes. In the long-term, the results obtained here may help to reduce the frequency of subfertility in beef herds, reducing the associated economic losses caused by this condition.

Analysis of meiotic segregation by triple-color fish on both total and motile sperm fractions in a t(1p;18) river buffalo bull

Chromosomal aberrations are relatively frequent pathologies in both humans and animals. Among them, translocations present a specific meiotic segregation pattern able to give a higher percentage of unbalanced gametes that can induce fertility problems. In this study, the meiotic segregation patterns of 1p, 1q and 18 Bubalus bubalis chromosomes were analyzed in both total sperm fraction and motile sperm fraction of a t(1p;18) carrier and a control bulls by triple-color FISH analysis with a pool of specific BAC probes. The frequencies of each total sperm fraction products in the carrier resulting from alternate, adjacent I, adjacent II and 3:1 segregation were 39%, 20%, 1% and 38%, respectively. On the other hand, the frequencies of each motile sperm fraction products in the carrier resulting from alternate, adjacent I, adjacent II and 3:1 segregation were 93%, 5%, 0% and 2%, respectively. The frequencies of normal sperms in the carrier were 27% and 69% in total sperm fraction and motile sperm fraction, respectively. The frequencies detected in motile sperm fraction were also validated by comparison with bull’s progeny. To our knowledge, this is the first report on the meiotic segregation patterns in motile sperm fractions of B. bubalis bull carrying a chromosomal translocation. These data suggest that translocation has a very limited effect on aneuploidy in the gametes, and therefore, on the reproductive abilities of the bull.