The effect of embryonic death rates in cattle on the efficacy of estrus synchronization programs

Relationship between quantity of IFNT estimated by IFN-stimulated gene expression in peripheral blood mononuclear cells and bovine embryonic mortality after AI or ET

BACKGROUND

Interferon tau (IFNT), which is secreted into the uterine cavity during the maternal recognition period (MRP), is a key factor for establishment of pregnancy. The present study aims to clarify the relationship between the ability of a bovine conceptus to produce IFNT during the MRP and the conceptus's ability to establish pregnancy.

METHODS

In the first experiment, IFNT (0, 500, or 1000 micrograms) was administered into the uterine horn ipsilateral to the CL 16 or 17 d after standing estrus, and mRNA levels of IFN-stimulated gene 15-kDa protein (ISG15) and Mx2 in peripheral blood mononuclear cells (PBMCs) were determined. In the second experiment, we investigated ISG15 mRNA expression in PBMCs during the MRP in cattle after either artificial insemination (AI) or embryo transfer (ET).

RESULTS

Intrauterine administration of IFNT stimulated ISG15 and Mx2 gene expressions in PBMCs in cattle, and there was a positive correlation between the expressions of peripheral markers and the quantity of IFNT administered. In pregnant and normal interestrous interval (< 25 d) cattle (nIEI cattle), expression levels of the ISG15 gene showed similar patterns after AI and ET, and ISG15 mRNA expression was increased in pregnant cattle but unchanged in nIEI cattle. In contrast, ISG15 gene expression in extended interestrous interval (greater than or equal to 25 d) cattle (eIEI cattle) differed after ET compared with AI. In eIEI cattle after ET, ISG15 gene expression increased, such that the value on day 18 was intermediate between those of pregnant and nIEI cattle. In eIEI cattle after AI, ISG15 gene expression did not increase throughout the observation period.

CONCLUSIONS

The results of the current study indicate that the quantity of conceptus-derived IFNT can be estimated by measuring ISG15 mRNA levels in PBMCs from cattle. Using this approach, we demonstrate that ISG15 gene expression during the MRP in eIEI cattle differed after ET compared with AI. In addition, the modest increase in ISG15 gene expression in eIEI cattle after ET suggests that late embryo losses were due to delayed or insufficient growth of the conceptus during the MRP in cattle.

Relationship between oxidative stress and the success of artificial insemination in dairy cows in a pasture-based system

This study was designed to evaluate whether the outcome of artificial insemination (AI) was affected by the metabolic and oxidative status of dairy cows. Seventy-nine inseminations in 40 cows, were classified, on the basis of blood progesterone (P4) and pregnancy-associated glycoprotein (PAG) concentrations and clinical confirmation of pregnancy into, three categories: (1) positive (AI+, resulted in pregnancy, n=26; 33%), (2) negative (AI-, did not result in pregnancy, n=49; 62%), and (3) embryonic mortality (EM, n=4; 5%). Reactive oxygen metabolites, biological antioxidant potential, oxidative stress index, body condition score, glucose, total proteins, albumin, urea, non-esterified fatty acids (NEFAs), cholesterol, triglycerides, haptoglobin and advanced oxidative protein products (AOPPs) were measured on the day of AI (day 0), and 30 and 42 days later. Cows with EM had lower BCS scores (2.5) than AI+ (2.8) and AI- (2.9) cows (P<0.05). During the post-partum period, body condition score (BCS) increased and NEFAs decreased (P<0.05) suggesting a recovery from the negative energy balance (NEB). The only significant differences found were that the mean concentration of AOPPs was higher and that of albumin lower in EM cows than in AI+ and AI- (P<0.05) animals. Plasma concentration of reactive oxygen metabolites and biological antioxidant potential were not related to AI outcome. Further studies are required to confirm this finding and to clarify the role of oxidative status on cows' fertility.

The use of endocrine treatments to improve pregnancy rates in cattle

Reproduction is critical for the success of both dairy and beef cattle production. Inadequate reproduction impairs profitability by compromising production, delaying genetic progress and increasing expenses. A major impediment to the use of artificial insemination (AI) is the ability to detect oestrus for optimum timing of breeding. However, increased understanding of the bovine oestrous cycle has led to the development of reproductive programmes that allow precise synchrony of follicle development, luteal regression and ovulation. The advent of timed-AI protocols revolutionised reproductive management in dairy and beef herds. It allows for AI at a more desired time post partum despite oestrous cyclicity. It also allows for pre-determined re-insemination of cows diagnosed as not pregnant. In subfertile cows, such as the post partum, anoestrous beef cow and the high-producing dairy cow, strategic hormone supplementation has been used to overcome hormone deficiencies and improve pregnancy rates. Several physiological windows have been identified to optimise fertility in synchronisation programmes and they include, but are not limited to, follicle turnover, synchrony of follicular development, length of dominance, progesterone concentrations during development of the ovulatory follicle, luteal regression, peri-ovulatory steroid concentrations, length of pro-oestrus, synchrony of ovulation and AI, and progesterone rise after ovulation.

Differential expression of heat shock protein genes and their splice variants in bovine preimplantation embryos

Heat shock proteins (HSP) are among the first proteins produced during embryonic development and are crucial to cell function; their activities include folding, unfolding, transport, and localization of proteins and differentiation and regulation of the embryonic cell cycle. Although HSP have been extensively studied in humans and mice, limited information exists on the roles of these genes in bovine embryos. As such, the objectives of this study were to profile the expression of HSP and their splice variants in bovine embryos (degenerates vs. blastocysts) and to carry out association analysis with fertility traits. Quantitative real time PCR analysis revealed differences in expression that ranged from 1.5- to 7.6-fold in degenerate embryos compared with blastocysts. Interestingly, all members of the HSP40 family were found to be upregulated in degenerate embryos. Analysis of current bovine Ensembl data showed that 13 HSP genes have 1 transcript each, 2 genes have 2 transcripts each, and 2 have 3 transcripts each. Some splice variants show differential expression between degenerate embryos and blastocysts, whereas others were not expressed at all in embryos, which implies different functions of these transcripts in embryonic development. The most significant differentially expressed genes were further investigated for association with fertility and development traits. Single nucleotide polymorphisms in DNAJC15 and DNAJC27 were found to be associated with blastocyst rate and fertilization rate, respectively. Collectively, the roles of HSP in fertilization and early development of cattle embryos are important.

Short communication: expression and alternative splicing of POU1F1 pathway genes in preimplantation bovine embryos

Early embryo loss is a major contributing factor to cow infertility and that 70 to 80% of this loss occurs between d 8 and 16 postfertilization. However, little is known about the molecular mechanisms and the nature of genes involved in normal and abnormal embryonic development. Moreover, information is limited on the contributions of the genomes of dams and of embryos to the development and survival of preimplantation embryos. We hypothesized that proper gene expression level in the developing embryo is essential for embryo survival and pregnancy success. As such, the characterization of expression profiles in early embryos could lead to a better understanding of the mechanisms involved in normal and abnormal embryo development. To test this hypothesis, 2 d-8 embryo populations (degenerate embryos and blastocysts) that differed in morphology and developmental status were investigated. Expression levels of POU1F1 pathway genes were estimated in 4 sets of biological replicate pools of degenerate embryos and blastocysts. The OPN and STAT5A genes were found to be upregulated in degenerate embryos compared with blastocysts, whereas STAT5B showed similar expression levels in both embryo groups. Analysis of splice variants of OPN and STAT5A revealed expression patterns different from the total expression values of these genes. As such, measuring expression of individual transcripts should be considered in gene expression studies.

Reproductive performance of anoestrous high-producing dairy cows improved by adding equine chorionic gonadotrophin to a progesterone-based oestrous synchronizing protocol

This study sought to improve the reproductive performance of anoestrous high-producing dairy cows by including equine chorionic gonadotrophin (eCG) after progesterone-releasing intravaginal device (PRID) removal. In Experiment I, 806 cows at 51-57 days post-partum were randomly assigned to a PRID (treated with PRID), PRID-500 (treated with PRID plus 500 IU of eCG) or PRID-750 (treated with PRID plus 750 IU of eCG) group. In Experiment II, 422 cows showing a long anoestrus period (animals with no oestrus signs nor luteal tissue 35 days before treatment) were randomly assigned to the PRID, PRID-500 or PRID-750 groups. The dependent variables considered in binary logistic regression analyses for both experiments were the rates of oestrus, ovulation and conception after treatment, the cumulative conception rate on Day 120 post-partum and pregnancy loss. In Experiment I, interaction between treatment and season showed a significant effect on the oestrous response. Thus, during the warm season, PRID group cows were 8.9 times more likely to express oestrus than the remaining cows. Moreover, inseminated cows with two or more corpora lutea 8-14 days after treatment were more likely to become pregnant (by a factor of 2.4) than cows with a single corpus luteum. Finally, cows without luteal structures treated with PRID were 0.4 less likely to be pregnant on Day 120 post-partum, compared with the remaining cows. In Experiment II, cows in the PRID group treated during the warm or cool season were less likely to exhibit oestrus (by a factor of 0.06 or 0.2, respectively) or ovulate (by a factor of 0.004 or 0.14, respectively) than the remaining cows. In conclusion, in anoestrous cows in both experiments, the addition of eCG to the use of an intravaginal progesterone device to induce oestrus was beneficial. The recommended dose of eCG is 500 IU.

Concentration of progesterone during the development of the ovulatory follicle: I. Ovarian and embryonic responses

Objectives were to evaluate the effects of differing progesterone concentrations during follicle development on follicular dynamics, fertilization, and embryo quality. Lactating Holstein cows (n=154) were assigned randomly to 1 of 2 treatments. Cows underwent a presynchronization of the estrous cycle composed of an injection of GnRH concurrently with the placement of a progesterone insert, an injection of PGF(2α) and insert removal 7 d later, and a second injection of GnRH 48 h later (study d -16). All cows were then submitted to a hormonal protocol identical to the presynchronization program starting on d 7 of the estrous cycle (study d -9). Cows enrolled in the high progesterone (HP) treatment received no further treatment. Cows in the low progesterone (LP) treatment received additional PGF(2α) injections on study d -14, -13.5, and -13 and again on study d -9, -7, -6.5, and -6. Ovaries were evaluated by ultrasonography, and blood was sampled for concentrations of progesterone and estradiol throughout the study. Uteri were flushed 6 d after artificial insemination (AI) and recovered oocytes-embryos were evaluated. Concentrations of progesterone were less for LP cows from study d -7 to -2; concentrations of estradiol at PGF(2α) and at the last GnRH of synchronization were greater for LP than HP. The proportion of cows in estrus at AI was greater for LP than for HP (38.0 vs. 5.3%). Ovulatory follicles of LP cows had larger diameters at the injections of PGF(2α) (17.2 vs. 14.6mm) and final GnRH (19.4 vs. 16.9%) of the synchronization, which resulted in a larger diameter of the corpus luteum 6 d after AI (24.3 vs. 22.6mm). Double ovulation after the last GnRH of the synchronization was increased in LP (18.6%) compared with HP (4.5%). Fertilization rate was similar and averaged 82.7%. The proportion of embryos and oocytes-embryos classified as grades 1 and 2, proportion of degenerated embryos, and unfertilized-degenerated oocytes-embryos were not different between LP and HP. Number of blastomeres did not differ between LP and HP, but the proportion of live blastomeres tended to be less for LP than HP (94.2 vs. 98.7%). Reducing progesterone concentrations during the synchronization program altered concentrations of estradiol and follicular dynamics, but resulted in similar fertilization and only minor changes in embryo quality.

Association of milk protein genes with fertilization rate and early embryonic development in Holstein dairy cattle

Concomitant with intensive selection for increased milk yield, reproductive performance of dairy cows has declined in the last decades, in part due to an unfavourable genetic relationship between these traits. Given that the six main milk protein genes (i.e. whey proteins and caseins) are directly involved in milk production and hence have been a target of the strong selection aimed at improving milk yield in dairy cattle, we hypothesized that these genes could show selection footprints associated with fertility traits. In this study, we used an in-vitro fertilization (IVF) system to test genetic association between 66 single nucleotide polymorphisms (SNPs) in the four caseins (αS1-casein, αS2-casein, β-casein and κ-casein) and the two whey protein genes (α-lactalbumin and β-lactoglobulin) with fertilization rate and early embryonic development in the Holstein breed. A total of 6893 in-vitro fertilizations were performed and a total of 4661 IVF embryos were produced using oocytes from 399 ovaries and semen samples from 12 bulls. Associations between SNPs and fertility traits were analysed using a mixed linear model with genotype as fixed effect and ovary and bull as random effects. A multiple testing correction approach was used to account for the correlation between SNPs due to linkage disequilibrium. After correction, polymorphisms in the LALBA and LGB genes showed significant associations with fertilization success and blastocyst rate. No significant associations were detected between SNPs located in the casein region and IVF fertility traits. Although the molecular mechanisms underlying the association between whey protein genes and fertility have not yet been characterized, this study provides the first evidence of association between these genes and fertility traits. Furthermore, these results could shed light on the antagonistic relationship that exists between milk yield and fertility in dairy cattle.

Nutrition × reproduction interaction in pasture-based systems: is nutrition a factor in reproductive failure?

Dairy cow fertility has declined in recent decades, coincidental with large increases in milk production. Cows take longer to return to oestrus, display poorer signs of oestrus, have greater early embryo loss, and may have poorer conception rates. The problem is often considered to be nutritional, at least in part, and, therefore, can be corrected through dietary adjustment. Although acknowledged as highly digestible, high quality pastured forages tend to be low in non-structural carbohydrates (NSC), high in rumen degradable protein and the temporal supply may not be adequate for cow demand at key times; diet adjustment is often recommended to overcome these limitations. The interaction between nutrition and reproduction is poorly defined, however, and study results are often contradictory. Hypothesised limitations to pastured forages within a grazing system will be discussed, and the likely impact of nutritional adjustment on pre- and post-ovulatory reproductive processes examined. The effect of energy balance, carbohydrate type, protein and fat on reproductive outcomes will be considered. Nutrition is an important component of successful reproduction, but dietary adjustment to improve pregnancy rates is complicated, and merely offering pastured cows a supplement is unlikely to result in large effects. Conclusions indicate that care must be taken in interpreting associative analyses and in applying results from different farming systems.

Effects of resynchronization programs on pregnancy per artificial insemination, progesterone, and pregnancy-associated glycoproteins in plasma of lactating dairy cows

Objectives were to develop a timed artificial insemination (TAI) resynchronization program to improve pregnancy per AI and to evaluate responses of circulating progesterone and pregnancy-associated glycoproteins in lactating cows. Cows (n=1,578) were presynchronized with 2 injections of PGF2alpha, given 14 d apart starting on d 45+/-3 postpartum, followed by Ovsynch [2 injections of GnRH 7 d before and 56 h after injection of PGF2alpha, TAI 16 h after second injection (d 0)]. The Resynch-treated cows received an intravaginal progesterone insert from d 18 to 25, GnRH on d 25, and pregnancy diagnosis on d 32, and nonpregnant cows received PGF2alpha., GnRH 56 h later, and TAI 16 h later (d 35). The control cows were diagnosed for pregnancy on d 32 and nonpregnant cows received GnRH, PGF2alpha 39 d after TAI, GnRH 56 h later, and TAI 16 h later (d 42). Pregnancy was reconfirmed on d 60 after AI. Ovarian structures were examined in a subset of cows at the time of GnRH and PGF2alpha injections. Blood samples for analyses of progesterone and pregnancy-associated glycoproteins were collected every 2 d from d 18 to 30 in 100 cows, and collection continued weekly to d 60 for pregnant cows (n=43). Preenrollment pregnancies per AI on d 32 did not differ for cows subsequently treated as Resynch (45.8%, n=814) and control (45.9%, n=764), and pregnancy losses on d 60 were 6.7 and 4.0%, respectively. Resynchronized service pregnancy per AI (36%, n=441; 39.5%, n=412) and pregnancy losses (6.3 and 6.7%) did not differ for Resynch and control treatments, respectively. Days open for pregnant cows after 2 TAI were less for the Resynch treatment than for the control treatment (96.2+/-0.82 vs. 99.5+/-0.83 d). Cows in the Resynch treatment had more large follicles at the time of GnRH. The number of corpora lutea did not differ between treatments at the time of PGF2alpha. Plasma progesterone for pregnant cows was greater for Resynch cows than for control cows (18-60 d; 6.6 vs. 5.3 ng/mL), and plasma concentrations of progesterone on d 18 were greater for pregnant cows than for nonpregnant cows (5.3 vs. 4.3 ng/mL). Plasma pregnancy-associated glycoproteins during pregnancy were lower for cows in the Resynch treatment compared with control cows on d 39 (2.8 vs. 4.1 ng/mL) and 46 (1.3 vs. 3.0 ng/mL). Cows pregnant on d 32 that lost pregnancy by d 60 (n=7) had lower plasma concentrations of pregnancy-associated glycoproteins on d 30 than cows that maintained pregnancy (n=36; 2.9 vs. 5.0 ng/mL). Pregnancy-associated glycoproteins on d 30 (>0.33 ng/mL) were predictive of a positive d 32 pregnancy diagnosis (sensitivity=100%; specificity=90.6%). In conclusion, Resynch and control protocols had comparable pregnancy per AI for first and second TAI services, but pregnancy occurred 3.2 d earlier in the Resynch group because inseminations in the Resynch treatment began 7 d before those in the control treatment. Administration of an intravaginal progesterone insert, or GnRH, or both increased progesterone during pregnancy. Dynamics of pregnancy-associated glycoproteins were indicative of pregnancy status and pregnancy loss.

A review of factors that impact on the capacity of beef cattle females to conceive, maintain a pregnancy and wean a calf-Implications for reproductive efficiency in northern Australia

A review of factors that may impact on the capacity of beef cattle females, grazing semi-extensive to extensive pastures in northern Australia, to conceive, maintain a pregnancy and wean a calf was conducted. Pregnancy and weaning rates have generally been used to measure the reproductive performance of herds. However, this review recognises that reproductive efficiency and the general measures associated with it more effectively describe the economic performance of beef cattle enterprises. More specifically, reproductive efficiency is influenced by (1) pregnancy rate which is influenced by (i) age at puberty; (ii) duration of post-partum anoestrus; (iii) fertilisation failure and (iv) embryo survival; while (2) weight by number of calves per breeding female retained for mating is influenced by (i) cow survival; (ii) foetal survival; and (iii) calf survival; and (3) overall lifetime calf weight weaned per mating. These measures of reproductive efficiency are discussed in depth. Further, a range of infectious and non-infectious factors, namely, environmental, physiological, breed and genetic factors and their impact on these stages of the reproductive cycle are investigated and implications for the northern Australian beef industry are discussed. Finally, conclusions and recommendations to minimise reproductive inefficiencies based on current knowledge are presented.

Comparison of commercial ELISA blood tests for early pregnancy detection in dairy cows

The objective of the present study was to compare two commercially available blood-based pregnancy tests, namely BioPRYN, an ELISA for pregnancy-specific protein B (PSPB), and an ELISA for pregnancy-associated glycoprotein (PAG), for early pregnancy diagnosis in dairy cattle using transrectal ultrasonography as a gold standard. Transrectal ultrasonography was conducted 26-58 days after artificial insemination (AI) in 197 cattle from 19 farms. Concurrently, a blood sample was collected for determination of serum PSPB and PAG. Transrectal palpation was performed approximately 120 days after AI to verify that pregnancy was maintained. For PSPB and PAG, there were no significant differences (P>0.05) in sensitivity (98.0 and 97.8%), specificity (97.1 and 91.2%), positive predictive values (99.3 and 97.8%), negative predictive values (91.9 and 91.2%) and accuracy (97.8 and 96.4%). In conclusion, the two blood pregnancy assays were equally efficacious and were highly accurate (based on transrectal ultrasonography as the gold standard).

Use of a stochastic simulation model to assess effects of diagnostic specificity of systems for detecting ovulating cows on herd reproductive performance in year-round calving dairy herds

Many automated systems for detecting ovulating cows in dairy herds require decisions when designing algorithms and selecting cutpoints that require a compromise between diagnostic sensitivity (probability of classifying an ovulating cow as ovulating) and diagnostic specificity [daily probability of not classifying a non-ovulating cow (whether open or pregnant but not yet diagnosed as pregnant) as ovulating]. Because sensitivity must be moderately high, this compromise often results in specificity below 100%. However, little is understood about the effects of reduced specificity on herd reproductive performance. A stochastic model was developed that simulates the reproductive process in a year-round calving dairy herd to assess effects of changes in specificity at various combinations of sensitivity and conception rate (proportion of inseminations resulting in pregnancy) on herd reproductive measures of economic importance. The model included effects of inseminations in pregnant cows on probability of conceptus loss, and variation in the interval from conceptus loss to next ovulation (i.e. the next opportunity to reconceive). Using moderate assumptions of the probability of conceptus loss following insemination in pregnant cows, reductions in specificity from 99.9 to 99.5, 99, 98 and 97%, resulted in decreases in mean 100 day in-calf rate (100DICR; the proportion of cows with a positive pregnancy diagnosis to an insemination on or before 100 days since calving) of 1.2, 3.3, 6.8 and 9.7 percentage points, respectively. These same reductions in Sp resulted in increases in mean 200 day not in-calf rate (200DNICR; the proportion of cows with negative pregnancy diagnosis results to all inseminations on or before 200 days since calving) of 0.5, 1.6, 3.6 and 6 percentage points, and increases in mean number of inseminations per calving (Insems/Calving; the total number of inseminations in the herd divided by the number of cows that recalved) by factors of 1.2, 1.5, 2.1 and 2.8, respectively. The relationship between specificity for detecting ovulating cows and the 100DICR, 200DNICR and Insems/Calving was sensitive to changes in the probability of conceptus loss following inseminations in pregnant cows. However, even with conservative assumptions, specificity still had important effects on 100DICR and 200DNICR. Varying parameters for the interval from conceptus loss to next ovulation had little effect on the relationships between specificity and these measures. These results demonstrate that specificity is an important consideration when designing algorithms and selecting cutpoints in automated systems for detecting ovulating cows. Low specificity not only increases Insems/Calving but also prolongs intervals from calving to the establishment of a sustained pregnancy resulting in substantial reductions in 100DICR and increases in 200DNICR. This model could assist when determining economically optimal combinations of ovulation detection sensitivity and specificity when developing automated systems for selecting ovulating cows in commercial herds.

Ovarian follicle diameter at timed insemination and estrous response influence likelihood of ovulation and pregnancy after estrous synchronization with progesterone or progestin-based protocols in suckled Bos indicus cows

The objectives of the present study were to evaluate factors associated with estrous synchronization responses and pregnancy per insemination (P/AI) in Bos indicus beef cows submitted to progesterone-based fixed-time artificial insemination (FTAI) protocols. A total of 2388 cows (1869 Nellore and 519 crossbred NellorexAngus) from 10 commercial farms were evaluated to determine the relationships among breed, body condition score (BCS) on the first day of the FTAI protocol, the occurrence of estrus between progesterone device removal and FTAI, and diameter of largest ovarian follicle (LF) at FTAI on estrous synchronization responses and P/AI. Cows (n=412 primiparous; 1976 multiparous) received an intravaginal device containing progesterone or an ear implant containing norgestomet (a progestin), and an injection of estradiol at the beginning of the estrous synchronization protocol. Body condition was scored using a 1-5 scale on the first day of the FTAI protocol and at 30-60 days postpartum. Females received 300IU of equine chorionic gonadotropin (eCG) and PGF(2alpha) on the day the progesterone device/implant was removed and were inseminated 48-60h later. At insemination, cows (n=2388) were submitted to an ultrasonographic exam to determine the diameter of the LF. Follicles were classified into four categories based on mean and standard deviation (SD) of the LF (LF1=two SD below the mean; LF2=mean minus one SD; LF3=mean plus one SD; LF4=two SD above the mean). Ovulation rate was determined in a subset of cows (n=813) by three consecutive ultrasonographic exams: (1) at time of progesterone device/implant removal, (2) at time of FTAI and (3) 48h after FTAI. Ovulation was defined as the disappearance of a large follicle (>or=8.0mm) that was previously recorded. Estrus was determined in a subset of the cows (n=445) by the activation of a detection of estrous patch placed on the tail head on the day of progesterone device/implant removal. Pregnancy was diagnosed 30 days after FTAI. Pregnancy was influenced (P=0.001) by follicle diameter [LF1=27.5% (81/295), LF2=46.6% (328/705), LF3=57.9% (647/1118), LF4=63.3% (171/270)] and the occurrence of estrus [estrus=67.7% (174/257) and no estrus=36.2% (68/188)]. Follicle diameter at FTAI influenced ovulation rate [LF1=42.5% (34/80), LF2=73.9% (161/218), LF3=95.8% (407/425), LF4=97.8% (88/90)], the occurrence of estrus [LF1=54.8% (51/93), LF2=33.6% (43/128), LF3=68.9% (126/183), LF4=90.2% (37/41)] and P/AI among cows that had ovulations [LF1=32.4% (11/34), LF2=50.3% (81/161), LF3=60.0% (244/407), LF4=68.2% (60/88)]. Improving estrous responses between progesterone device withdrawal and FTAI and increasing the diameter of the LF at FTAI may be important aspects to achieve improved estrous synchronization responses and P/AI following progesterone/progestin and estradiol based FTAI protocols in suckled Bos indicus cows.

Genetic parameters for anovulation and pregnancy loss in dairy cattle

The objectives were to estimate heritabilities and genetic variances for anovulation at ~50 d in milk and pregnancy loss occurring between first and second pregnancy diagnoses after artificial insemination. Data were originally collected for trials on reproductive management. Anovulation data consisted of 5,818 records from 13 studies in 8 herds with an overall prevalence of 23.3%. A Bayesian approach using Markov Chain Monte Carlo methods was used in mixed threshold models for both traits. The statistical model for anovulation included fixed effects [parity, herd-study-treatment, and body condition score (BCS)], covariates (inbreeding and milk yield), and random effects (sire and residual). A second statistical model included all terms in the first model except BCS. In addition, 2 bivariate, mixed sire models were used to analyze anovulation with BCS and anovulation with milk yield. The posterior mean heritability estimate for anovulation was 0.171 [posterior standard deviation (PSD) = 0.052]. Correlations of anovulation with milk yield were as follows: genetic = 0.168, PSD = 0.187; residual = -0.046, PSD = 0.022; and phenotypic = -0.036. Bivariate analysis of BCS with anovulation showed a genetic correlation (-0.301, PSD = 0.177) and phenotypic correlation (-0.192, PSD = 0.019). Pregnancy-loss data consisted of 3,775 records from 14 studies in 8 herds with an overall prevalence of 14.4%. Analysis of pregnancy loss used a sire-maternal grandsire threshold model with embryo survival as the subject of analysis. Independent variables consisted of fixed effects (parity and herd-study), covariates (embryo and maternal inbreeding), and random effects (sire of embryo, maternal grandsire of embryo, and residual). In addition, separate sire models were analyzed using embryo as the subject and cow as the subject of analysis. The sire-maternal grandsire model yielded a heritability for direct effect of 0.489 (PSD = 0.221) and for maternal effects of 0.166 (PSD = 0.113). In this study, the breeding value variance for embryo effects was 3 times the breeding value variance for maternal effects, indicating that, at the level of breeding values, the embryo's ability to survive has a greater effect on pregnancy loss than does the cow's ability to maintain the pregnancy. These results suggest that genetic improvement of reproductive performance could be enhanced by selection for fundamental measures such as abnormally long periods of postpartum anovulation and pregnancy loss. Larger studies of these traits are needed to obtain parameter estimates with greater precision.

Effect of increasing amounts of supplemental progesterone in a timed artificial insemination protocol on fertility of lactating dairy cows

The objectives were to evaluate the effect of supplemental progesterone during a timed artificial insemination (TAI) protocol on pregnancy per insemination and pregnancy loss. Lactating dairy cows from 2 dairy herds were presynchronized with 2 injections of PGF(2alpha) 14 d apart, and cows observed in estrus following the second PGF(2alpha) injection were inseminated (n = 1,301). Cows not inseminated by 11 d after the end of the presynchronization were submitted to the TAI protocol (d 0 GnRH, d 7 PGF(2alpha), d 8 estradiol cypionate, and d 10 TAI). On the day of the GnRH of the TAI protocol (study d 0), cows were assigned randomly to receive no exogenous progesterone (control = 432), one controlled internal drug-release (CIDR) insert (CIDR1 = 440), or 2 CIDR inserts (CIDR2 = 440) containing 1.38 g of progesterone each from study d 0 to 7. Blood was sampled on study d 0 before insertion of CIDR for determination of progesterone concentration in plasma, and cows with concentration <1.0 ng/mL were classified as low progesterone (LP) and those with concentration > or =1.0 ng/mL were classified as high progesterone (HP). From a subgroup of 240 cows, blood was sampled on study d 3, 7, 17 and 24 and ovaries were examined by ultrasonography on study d 0 and 7. Pregnancy was diagnosed at 38 +/- 3 and 66 +/- 3 d after AI. Data were analyzed including only cows randomly assigned to treatments and excluding cows that were inseminated after the second PGF(2alpha) injection. The proportion of cows classified as HP at the beginning of the TAI protocol was similar among treatments, but differed between herds. Concentrations of progesterone in plasma during the TAI protocol increased linearly with number of CIDR used, and the increment was 0.9 ng/mL per CIDR. The proportion of cows with plasma progesterone > or =1.0 ng/mL on study d 17 was not affected by treatment, but a greater proportion of control than CIDR-treated cows had asynchronous estrous cycles following the TAI protocol. Treatment with CIDR inserts, however, did not affect pregnancy at 38 +/- 3 and 66 +/- 3 d after AI or pregnancy loss.

Comparison of ovulation, fertilization and embryonic survival in low-fertility beef cows compared to fertile females

The objective was to determine physiological causes of low fertility in beef cows. Fertility was compared between low-fertility cows (34 British cows and 64 Brahman crossbred cows; cows that did not get pregnant when mated to fertile bulls in one or two previous breeding seasons); fertile cows (16 Brahman crossbreds; cows having a calf in several of the preceding breeding seasons), and virgin heifers (45 Brahman crossbreds, 2 yr of age). Females were mated to fertile bulls and killed 3 or 34 d after breeding to obtain reproductive tracts. There were no significant differences among groups in rates of ovulation or fertilization. Overall, 14% of females failed to ovulate and 24% that ovulated failed to undergo fertilization. The proportion of cows that were not detected in estrus before Day 34 of pregnancy was lower (P<0.01) for low-fertility British cows (5 of 16 cows, 31%) than for other groups, including low-fertility Brahman crossbred cows (23/32, 72%), fertile cows (8/9, 89%), and heifers (21/24, 88%). All cows that did not return to estrus by Day 34 had an identifiable conceptus. The proportion of conceptuses recovered at Day 34 that were classified as normal (weight and length) was lower (P<0.05) for cows with low fertility (British: 2/5, 40%; Brahman crossbred: 9/23, 39%) than for fertile cows (8/8, 100%) or heifers (18/21; 86%). Similarly, the proportion of cows in which a normal embryo was recovered (cows with normal embryos/number of cows mated) was lower (P<0.001) for low-fertility British cows (2/16, 13%) and low-fertility Brahman crossbred cows (9/32, 28%) than for fertile cows (8/9, 89%) and heifers (18/24, 75%). In conclusion, cows that were infertile in previous breeding seasons did not experience reduced ovulation or fertilization rates, but had greater embryonic mortality. These data highlighted the importance of ovulation and fertilization failure and embryonic mortality as important determinants of pregnancy success. Moreover, increased embryonic loss after Day 34 contributed to infertility in low-fertility cows.

Effects of signal transducer and activator of transcription (STAT) genes STAT1 and STAT3 genotypic combinations on fertilization and embryonic survival rates in Holstein cattle

Infertility is a major cause of dairy cow culling and economic loss. Signal transducer and activator of transcription (STAT) proteins are transcription factors that play an important role in fertility and early embryonic development, among many other functions. Previous studies have reported the association of several genes from the JAK/STAT signaling pathway with fertility traits in cattle. The STAT1 and STAT3 genes are members of this pathway and are known to interact with each other by forming a heterodimer complex that enters the nucleus and controls expression of specific genes. Thus, the objective of this study was to investigate the effects of the interactions between polymorphisms in these genes on fertilization and early embryonic survival rates using an in vitro fertilization system. A total of 7,519 oocytes, collected from 445 ovaries, were exposed to sperm and a total of 5,075 embryos were produced. Fertilization rate was calculated as the number of cleaved embryos at 48 h post-fertilization out of the total number of oocytes exposed to sperm. Early embryonic survival rate of embryos was calculated as the number of blastocysts on d 7 of development out of the total number of embryos cultured. Effects of ovary genotypes on fertilization and early embryonic survival rates were evaluated. Single-SNP analysis revealed a statistically significant association between SNP25402 in STAT3 and fertilization rate. Oocytes produced from ovaries with AA genotype showed a 0.701 fertilization rate versus 0.666 and 0.663 for oocytes produced from AC and CC ovaries, respectively. The interaction between STAT3 SNP (SNP19069/SNP25402) was highly significant for survival rate but not for fertilization rate. Also, the interaction between STAT1 SNP and SNP19069 was highly significant for survival rate. Genotype combinations found to promote fertilization and embryonic survival could be incorporated into breeding programs aimed at improving fertility performance in dairy cattle.

Effects of cumulative stressful and acute variation episodes of farm climate conditions on late embryo/early fetal loss in high producing dairy cows

The aim of this study was to determine possible relationships between farm climate conditions, recorded from day 0 to day 40 post-artificial insemination (AI), and late embryo/early fetal loss in high producing dairy cows. Pregnancy was diagnosed by rectal ultrasonography between 28 and 34 days post-AI. Fetal loss was registered when a further 80- to 86-day diagnosis proved negative. Climate variables such as air temperature and relative humidity (RH) were monitored in the cubicles area for each 30-min period. Temperature-humidity indices (THI); cumulative stressful values and episodes of acute change (defined as the mean daily value 1.2 times higher or lower than the mean daily values of the 10 previous days) of the climate variables were calculated. The data were derived from 759 cows in one herd. A total of 692 pregnancies (91.2%) carried singletons and 67 (8.8%) carried twins. No triplets were recorded. Pregnancy loss was recorded in 6.7% (51/759) of pregnancies: 5.6% (39/692) in single and 17.9% (12/67) in twin pregnancies. Using logistic regression procedures, a one-unit increase in the daily cumulative number of hours for the THI values higher than 85 during days 11-20 of gestation caused a 1.57-fold increase in the pregnancy loss, whereas the likelihood of fetal loss increased by a factor of 1.16 for each additional episode of acute variation for the maximum THI values during gestation days 0-40. THI values higher than 85 and episodes of acute variation for the maximum THI values were only recorded during the warm and cool periods, respectively. The presence of twins led to a 3.98-fold increase in pregnancy loss. In conclusion, our findings show that cumulative stressful and episodes of acute variation of climatic conditions can compromise the success of gestation during both the cool and warm periods of the year. Twin pregnancy was confirmed as a main factor associated with pregnancy loss.

Oestrus synchronisation and fixed time artificial insemination in beef heifers

To compare two oestrus synchronisation protocols in beef heifers presynchronised with two prostaglandin F2α (PG) treatments, 36 h after the second PG treatment one group (hCG-OB group; n = 112) received 250 IU of hCG and 0.5 mg of oestradiol benzoate (OB) followed by fixed time artificial insemination (FTAI) 30 h later. Additional oestrus detection (OD) and artificial insemination (AI) was done in this group for 3 days after FTAI; heifers rebred during this period were considered open to the FTAI. The Control group (n = 112) received only OD and AI for 6 days after the second PG treatment. Follicular size was measured at the time of AI in a subsample of heifers (59 in the hCG-OB group and 34 in the Control group). Results were evaluated separately either considering heifers pregnant at FTAI or those pregnant at FTAI + 3-day OD + AI. The FTAI conception rate was 45.5 vs 76.5% for the Control group (P < 0.0001) and pregnancy rates were 45.5 and 67.0% (P = 0.0014); FTAI + OD + AI conception rates were 63.4 and 76.2% (P = 0.0404) and pregnancy rates 63.4 and 62.8% (P = 0.5719) (hCG-OB and Control groups, respectively). There was a significant correlation (r = 0.713, P < 0.01) between follicle size at FTAI and pregnancy in the hCG-OB group, but not in the Control group (r = 0.3465, P > 0.1). In conclusion, acceptable synchronised conception rate and pregnancy rate were obtained by using this protocol, and the results were improved by complementing it with OD + AI for 3 days after FTAI.

Factors affecting plasma pregnancy-associated glycoprotein 1 concentrations throughout gestation in high-producing dairy cows

This study was designed to establish the factors, if any, which could affect plasma pregnancy-associated glycoprotein-1 (PAG-1) expression in a study population of 87 pregnant, high-producing dairy cows. The factors examined were: semen providing breed (Holstein-Friesian vs Limousin), outcome of gestation (male vs female newborn, and singleton vs twin pregnancies), lactation number, milk production at pregnancy diagnosis, plasma progesterone concentration, season of gestation (warm period, March-November vs cool period, December-February), and day of gestation (40, 90, 120, 150, 180 and 210). Pregnancy was diagnosed by transrectal ultrasound on day 40 post-insemination and by palpation per rectum on days 90, 120, 150, 180 and 210. Blood samples were collected from each animal immediately before each pregnancy diagnosis. The relative contributions of the different factors on PAG-1 concentrations were evaluated by GLM repeated measures analysis of variance. No significant effects of the herd, foetal sex, milk production, lactation number and plasma progesterone concentrations were observed. In contrast, twin pregnancy, the use of Limousin semen and conception during the cool period were correlated with significantly increased plasma PAG-1 concentrations throughout gestation. Our data indicate that both cow well-being during early placental development, determined in our conditions by reduced heat stress when conception occurred in the cool season, and crossbreed pregnancies lead to improved PAG-1 production throughout the gestation period.