Impact of heat stress on cow reproduction and fertility

Impact of Heat Stress on Oocyte Developmental Competence and Pre-Implantation Embryo Viability in Cattle

Rectal and vaginal temperatures are utilised in both in vivo and in vitro models to study the effects of heat stress on oocyte competence and embryo viability in cattle. However, uterine temperature increases by only 0.5 °C in heat-stressed cows, significantly lower than simulated increases in in vitro models. Temperature variations within oviducts and ovarian follicles during heat stress are poorly understood or unavailable, and evidence is lacking that oocytes and pre-implantation embryos experience mild (40 °C) or severe (41 °C) heat stress inside the ovarian follicle and the oviduct and uterus, respectively. Gathering detailed temperature data from the reproductive tract and follicles is crucial to accurately assess oocyte competence and embryo viability under realistic heat stress conditions. Potential harm from heat stress on oocytes and embryos may result from reduced nutrient availability (e.g., diminished blood flow to the reproductive tract) or other unidentified mechanisms affecting tissue function rather than direct thermal effects. Refining in vivo stress models in cattle is essential to accurately identify animals truly experiencing heat stress, rather than assuming heat stress exposure as done in most studies. This will improve model reliability and aid in the selection of heat-tolerant animals.

Livestock-Forest integrated system attenuates deleterious heat stress effects in bovine oocytes

Global warming poses significant challenges to the fertility of tropical dairy cattle. One promising approach to mitigate heat stress effects on reproductive function and reduce the carbon footprint is the use of integrated livestock-forest (ILF) systems. The aim of this study was to investigate the effects of two different systems, namely Full Sun (FS) and ILF, on maternal hyperthermia and oocyte quality of Holstein and Girolando heifers during the tropical summer season. The temperature-humidity index (THI) data revealed intense heat stress during the experiment. Both the system (P<0.01) and the breed (P<0.01) factors had a significant impact on vaginal temperature, being hyperthermia more pronounced in the FS system and in the Holstein breed. Over the five time points collected at a 33-day interval, we observed distinct patterns for ILF (P=0.65) and FS (P<0.001) systems, suggesting an adaptive response in animals kept in FS systems. Furthermore, oocyte quality assessment revealed an effect of the system for oocyte diameter (P<0.001) and levels of IGFBP2 (P<0.001), and caspase 3 levels showed a decrease in ILF compared to FS for both Holstein (P<0.001) and Girolando (P<0.001) breeds. Collectively, these parameters indicate that oocyte quality during the summer months was superior in animals maintained in the ILF system. In conclusion, the ILF system demonstrated promising results in attenuating maternal hyperthermia and mitigating its effects on oocyte quality. Additionally, our observations suggest that animals in the FS system may exhibit an adaptive response to heat stress.

A Review of the Effects of Stress on Dairy Cattle Behaviour

In this narrative review, the authors summarise the relationship between stress and behaviour and how dairy cattle cope with stressors. Based on the available literature, the most common stressors in intensive dairy cattle farming, such as pain, disease, heat stress, poor comfort caused by technology, and social stress, are surveyed. The authors describe how these stressors modify the behaviour of dairy cattle, influencing their feeding patterns, social interactions, and overall well-being. Additionally, the review explores the effectiveness of various coping mechanisms employed by dairy cattle to mitigate stress, including physiological adaptations and behavioural responses. This review is a valuable resource for understanding and grading stress in dairy cattle through behavioural reactions. Elucidating the intricate interplay between stressors and behaviour offers insights into potential interventions to improve animal welfare and productivity in dairy farming. Furthermore, this review highlights areas for future research, suggesting avenues for more comprehensive behavioural studies to enhance our understanding of stress management strategies in dairy cattle.

Unmasking seasonal cycles in a high-input dairy herd in a hot environment: How climate shapes dynamics of milk yield, reproduction, and productive status

This study aimed to predict the annual herd milk yield, lactation, and reproductive cycle stages in a high-input dairy herd in a zone with prolonged thermal stress. Also, the impact of climatic conditions on milk yield and productive and reproductive status was assessed. An autoregressive integrated moving average (ARIMA) model was used in data fitting to predict future monthly herd milk yield and reproductive status using data from 2014 to 2020. Based on the annual total milk output, the highest predicted percentage of milk yield based on the yearly milk production was in February (9.1%; 95% CI = 8.3-9.9) and the lowest in August (6.9%; 95% CI = 6.0-7.9). The predicted highest percentage of pregnant cows for 2021 was in May (61.8; 95% CI = 53.0-70.5) and the lowest for November (33.2%; 95% CI = 19.9-46.5). The monthly percentage of dry cows in this study showed a steady trend across years; the predicted highest percentage was in September (20.1%; CI = 16.4-23.7) and the lowest in March (7.5%; 4.0-11.0). The predicted days in milk (DIM) were lower in September (158; CI = 103-213) and highest in May (220; 95% CI = 181-259). Percentage of calvings was seasonal, with the predicted maximum percentage of calvings occurring in September (10.3%; CI = 8.0-12.5) and the minimum in April (3.2%; CI = 1.0-5.5). The highest predicted culling rate for the year ensuing the present data occurred in November (4.3%; 95% CI = 3.2-5.4) and the lowest in April (2.5%; 95% CI = 1.4-3.5). It was concluded that meteorological factors strongly influenced rhythms of monthly milk yield and reproductive status. Also, ARIMA models robustly estimated and forecasted productive and reproductive events in a dairy herd in a hot environment.

Unravelling the impact of heat stress on daughter pregnancy rate in Mehsana buffalo through innovative breeding interventions

Heat stress profoundly affects the reproductive success of buffaloes, which are vital for the dairy industry due to their unique anatomical and physiological characteristics, necessitating careful evaluation under such conditions. Hence, this guided our search for quantifying heat stress' impact on Mehsana buffaloes using the best THI model and evaluating sires' performance. Fertility records (days open converted to daughter pregnancy rate) were collected in the span of over 24 years, w.e.f. 1989 to 2012. Finally, 3070 records of first lactation cows, daughters of 117 sires from DURDA, Gujarat, India, were used in the analysis. Meteorological data were retrieved from IMD, Pune, to understand the relationship between daughter pregnancy rate (DPR) and heat stress indicators. Several heat stress models were compared based on R2, adjusted R2, AIC, and BIC values, and the impact of heat stress was quantified. The year was classified into different heat stress zones, viz., Non heat stress zone (NHSZ), Heat stress zone (HSZ), and critical heat stress zone (CHSZ), drawing from the findings of DPR and THI. The THI 4th model based on dry and wet bulb temperature was identified as the best-fit model, and DPR significantly changed (P < 0.01) by 1.14% per unit change in THI value based on the month of calving. The average EBVs of the sires for DPR were found to be 20.78% (NHSZ), 38.09% (HSZ), and 39.08% (CHSZ) using BLUP-SM and 20.78% (NHSZ), 37.30% (HSZ), and 38.87% (HSZ) using BLUP-AM. Subsequently, the optimum sire for each of the zones was prioritized. It is noteworthy that bulls that performed better in NHSZ did not perform as well in HSZ and CHSZ, and vice versa. This supports the possibility of evaluating bulls independently in each heat stress zone.

Factors at Insemination and Subsequent Conception of Cattle under Heat-Stress Tie-Stall Environments

This research aimed to compare the conception rates among AI at 12, 24, and 36 h after estrus in cattle living in tie-stall barns in a tropical environment. The second study was to determine factors at insemination at 24 h after estrus, including secondary signs of estrus behavior, reproductive tract characteristics, and heat-stress factors, in relation to conception. The study was conducted on 22 tie-stall dairy farms in Chiang Mai, Thailand. After secondary signs of estrus were observed, all farmers were informed for data collection at the insemination time. Repeated logistic regression models were used to determine factors associated with conception. The results revealed that cattle inseminated 24 h after estrus detection had the highest conception rate (67.5%). The study also found that cattle with three or two secondary estrus signs before insemination had a higher risk of conception than those with only one sign. Interestingly, there was an increased risk of conception when sticky or no cervical mucus was observed during insemination (OR = 6.85 and OR = 5.96, respectively). Moreover, increases in body temperature and ambient relative humidity were related to a decrease in the chances of conception. This study recommends delaying insemination to 24 h after the initiation of secondary estrus signs. Multiple signs of estrus, sticky cervical mucus, and lower body temperature increased conception risk in dairy cattle living in tie-stall barns in a heat-stress environment.

Effect of heat stress during the dry period on milk yield and reproductive performance of Holstein cows

This study aimed to determine the influence of heat stress during the dry period on milk yield and reproductive performance of Holstein cows in a hot environment. Breeding and milk production records of cows, as well as meteorological data between 2017 and 2020 from a commercial dairy herd (n = 12,102 lactations), were used to determine the relationship between climatic conditions during the dry period (average of the temperature-humidity index (THI) at the beginning, middle, and end of the dry period) and reproductive efficiency and milk yield traits. THI was divided into < 70 (no heat stress), 70-80 (moderate heat stress), and > 80 (severe heat stress). First-service pregnancy rate of cows decreased (P < 0.01) with increasing hyperthermia during the dry period (9.5, 7.3, and 3.4% for THI < 70, 70-80, and > 80, respectively). All-service pregnancy rate was highest (P < 0.01) for cows not undergoing heat stress during the dry period (60.2%) and lowest (42.6%) for cows with severe heat stress during the dry period. Cows not experiencing heat stress during the dry period required a mean ± SD of 5.6 ± 3.8 services per pregnancy compared with 6.5 ± 3.6 (P < 0.01) for cows subjected to THI > 80 during the dry period. Cows not suffering heat stress during the dry period produced more (P < 0.01) 305-day milk (10,926 ± 1206 kg) than cows subjected to moderate (10,799 ± 1254 kg) or severe (10,691 ± 1297 kg) heat stress during the dry period. Total milk yield did not differ (P > 0.10) between cows not undergoing heat stress (13,337 ± 3346 kg) and cows subjected to severe heat stress during the dry period (13,911 ± 4018 kg). It was concluded that environmental management of dry cows during hot months is warranted to maximize reproductive performance and milk yield in the following lactation.

Cellular and mitochondrial adaptation mechanisms in the colon of lactating dairy cows during hyperthermia

Heat stress causes barrier dysfunction and inflammation of the small intestine of several species. However, less is known about the molecular and cellular mechanisms underlying the response of the bovine large intestine to hyperthermia. We aimed to identify changes in the colon of dairy cows in response to constant heat stress using a proteomic approach. Eighteen lactating Holstein dairy cows were kept under constant thermoneutral conditions (16°C and 68% relative humidity [RH]; temperature-humidity index [THI] = 60) for 6 d (period 1) with free access to feed and water. Thereafter, 6 cows were equally allocated to (1) thermoneutral condition with ad libitum feeding (TNAL; 16°C, RH = 68%, THI = 60), (2) heat stress condition (HS; 28°C, RH = 50%, THI = 76) with ad libitum feeding, or (3) pair-feeding at thermoneutrality (TNPF; 16°C, RH = 68%, THI = 60) for another 7 d (period 2). Rectal temperature, milk yield, dry matter and water intake were monitored daily. Then, cows were slaughtered and colon mucosa samples were taken for proteomic analysis. Physiological data were analyzed by ANOVA and colon proteome data were processed using DESeq2 package in R. Rectal temperature was significantly higher in HS than in TNPF and TNAL cows in period 2. Proteomic analysis revealed an enrichment of activated pathways related to colonic barrier function and inflammation, heat shock proteins, AA metabolism, reduced overall protein synthesis rate, and post-transcriptional regulation induced by heat stress. Further regulations were found for enzymes of the tricarboxylic acid cycle and components of the mitochondrial electron transport chain, presumably to reduce the generation of reactive oxygen species, maintain cellular ATP levels, and prevent apoptosis in the colon of HS cows. These results highlight the cellular, extracellular, and mitochondrial adaptations of the colon during heat stress and suggest a dysfunction of the hindgut barrier integrity potentially resulting in a "leaky" colon.

Heat-Stress Impacts on Developing Bovine Oocytes: Unraveling Epigenetic Changes, Oxidative Stress, and Developmental Resilience

Extreme temperature during summer may lead to heat stress in cattle and compromise their productivity. It also poses detrimental impacts on the developmental capacity of bovine budding oocytes, which halt their fertility. To mitigate the adverse effects of heat stress, it is necessary to investigate the mechanisms through which it affects the developmental capacity of oocytes. The primary goal of this study was to investigate the impact of heat stress on the epigenetic modifications in bovine oocytes and embryos, as well as on oocyte developmental capacity, reactive oxygen species, mitochondrial membrane potential, apoptosis, transzonal projections, and gene expression levels. Our results showed that heat stress significantly reduced the expression levels of the epigenetic modifications from histone H1, histone H2A, histone H2B, histone H4, DNA methylation, and DNA hydroxymethylation at all stages of the oocyte and embryo. Similarly, heat stress significantly reduced cleavage rate, blastocyst rate, oocyte mitochondrial-membrane potential level, adenosine-triphosphate (ATP) level, mitochondrial DNA copy number, and transzonal projection level. It was also found that heat stress affected mitochondrial distribution in oocytes and significantly increased reactive oxygen species, apoptosis levels and mitochondrial autophagy levels. Our findings suggest that heat stress significantly impacts the expression levels of genes related to oocyte developmental ability, the cytoskeleton, mitochondrial function, and epigenetic modification, lowering their competence during the summer season.

Genome-wide association and functional annotation analysis for the calving interval in Nellore cattle

Calving interval (CI) measures the number of days between two consecutive calves of the same cow, and previous studies based on phenotype and pedigree data reported low heritability for this trait. However, the genetic architecture of CI in the Nellore breed was not evaluated based on genomic data. Thus, this study aimed to estimate the heritability based on genomic data and carry out a genome-wide association study (GWAS) for CI in the Nellore breed, using 12,599 pedigree records, 5078 CI records, and 3818 animals genotyped with 50k SNPchip panel. Both quality control and GWAS were performed in BLUPF90 family packages, which use the single-step genomic best linear unbiased predictor (ssGBLUP) method. The average CI was 427.6 days, with a standard deviation of 106.9 and a total range of 270-730 days. The heritability estimate was 0.04 ± 0.04. The p-values of GWAS analysis resulted in a genomic inflation factor (lambda) of 1.08. The only significant SNP (rs136725686) at the genome-wide level (p-value = 1.53E-06) was located on BTA13. Other 19 SNPs were significant at the chromosome-wide level, distributed on BTA1, 2, 3, 6, 10, 13, 14, 17, 18, 22, and 26. Functional annotation analysis found thirty-six protein-coding genes, including genes related to cell cycle (RAD21, BCAR3), oocyte function (LHX8, CLPX, UTP23), immune system (TXK, TEC, NFATC2), endocrine function (LRRFIP2, GPR158), estrous cycle (SLC38A7), and female fertility (CCK, LYZL4, TRAK1, FOXP1, STAC). Therefore, CI is a complex trait with small heritability in Nellore cattle, and various biological processes may be involved with the genetic architecture of CI in Nellore cattle.

The effect of heat stress on performance, fertility, and adipokines involved in regulating systemic immune response during lipolysis of early lactating dairy cows

The aim of this study was to assess the potential effect of heat stress on dairy cow productivity, fertility, and biochemical blood indices during the early lactation stage in a temperate climate. Additionally, the study aimed to determine the role of leptin and adiponectin in regulating the immune response accompanying lipolysis after calving in dairy cows. The study included 100 clinically healthy Polish Holstein-Friesian dairy cows selected based on parity and 305 d of milk yield from 5 commercial farms with similar herd management and housing systems. Prospective cohort data were recorded from calving day until 150 d in milk, and microclimate loggers installed inside the barns were used to record temperature and relative humidity data to calculate daily temperature-humidity index (THI) on the calving day, through +7, +14, and +21 d during early lactation. Additionally, monthly productive performance parameters such as milk yield, chemical composition, fatty acids composition, and fertility indices were analyzed. Results showed that the THI from calving day through +7, +14, and +21 d during early lactation was negatively associated with fertility parameters such as delayed first estrus postpartum and an elongated calving interval, respectively, by 29, 27, 25, and 16 d. Furthermore, an increase in THI value during early lactation was associated with an elongated artificially inseminated service period, days open, and intercalving period. Increasing THI from calving day (0 d) through +7, +14, and up to +21 d during early lactation was also linked to decreased milk yield by 3.20, 4.10, 5.60, and 5.60 kg, respectively. The study also found that heat stress during early lactation was associated with a lower body condition score in dairy cows and higher concentrations of leptin, nonesterified fatty acids, and β-hydroxybutyrate, accompanied by a drastic reduction in adipose tissue-secreted adiponectin levels after calving. Additionally, heat stress-induced lipolysis in adipose tissue caused an inflammatory response that increased biochemical blood indices associated with immune responses such as cytokines, acute phase proteins, and heat shock protein. These findings suggest that exposing dairy cows to heat stress during early lactation can negatively affect their productive performance, fertility, and biochemical blood indices in subsequent lactations. Thus, farm management changes should be implemented during early lactation to mitigate the negative consequences of heat stress occurrence.

Interval from Oestrus to Ovulation in Dairy Cows-A Key Factor for Insemination Time: A Review

This review describes the oestrus-to-ovulation interval, the possibility of predicting the time of ovulation, and the optimum time for insemination relative to oestrus in dairy cows. The duration of oestrus in dairy cows is approximately 8-20 h, with differences possibly related to the methods of oestrus detection and the frequency of observations. Most cows ovulate approximately 24-33 h after the onset of oestrus and 15-22 h after the end of oestrus. The interval from the preovulatory luteinising hormone (LH) surge to ovulation is approximately 4-30 h. Ovulation occurs when follicle diameter averages 18-20 mm. When it is possible to correctly determine the beginning of oestrus, artificial insemination can be performed utilizing the "a.m.-p.m. rule", and only one insemination may be applied. In cows with too long or too short oestrus-to-ovulation intervals, fertility can be compromised. One important factor that can alter the oestrus-to-ovulation interval is acute or chronic heat stress during the warm season. When there is a risk that insemination may occur too early or too late with respect to the time of ovulation, GnRH administration can be considered.

Negative photoperiod induces an increase in the number of ovulations in dairy cattle

This study sought to examine the impact of negative photoperiod on the incidence of multiple ovulations and pregnancies in dairy cattle. The study population consisted of 5,373 pregnant cows in their third or greater lactation that experienced their first post-partum pregnancy after spontaneous estrus. The positive photoperiod (increasing day-length) extends from December 22 to June 21, whereas the negative photoperiod (decreasing day-length) extends from June 22 to December 21. The odds ratios (ORs) for multiple ovulations and pregnancies in cows that became pregnant during the negative photoperiod and the remaining cows that became pregnant during the positive photoperiod were 1.4 and 1.3 (P < 0.0001), respectively. The ORs for cows that became pregnant ≥ 90 days in milk and the remaining cows that became pregnant < 90 days in milk were 4.3 and 4.1 (P < 0.0001), respectively. No significant differences were detected in the monthly rates of multiple ovulations or pregnancies during positive and negative photoperiods. Thus, the present study demonstrates that the ovarian function in cows is related to changes in day-length, with decreasing day-length being associated with greater multiple ovulation and pregnancy rates. The present study also shows that positive and negative photoperiods exhibit different trends. The results of this study are consistent with a growing body of work demonstrating the effects of photoperiod patterns on the reproductive physiology of cows, with clear implications for twin pregnancy prevention.

The Anti-Müllerian Hormone as Endocrine and Molecular Marker Associated with Reproductive Performance in Holstein Dairy Cows Exposed to Heat Stress

Anti-Müllerian hormone (AMH) is proposed as a biomarker for fertility in cattle, yet this associative relationship appears to be influenced by heat stress (HS). The objective was to test serum AMH and AMH-related single nucleotide polymorphisms (SNPs) as markers potentially predictive of reproductive traits in dairy cows experiencing HS. The study included 300 Holstein cows that were genotyped using BovineSNP50 (54,000 SNP). A genome-wide association study was then executed. Nine intragenic SNPs within the pathways that influence the AMH gene were found important with multiple comparisons adjustment tests (p < 1.09 × 10-6). A further validation study was performed in an independent Holstein cattle population, which was divided into moderate (MH; n = 152) and severe heat-stressed (SH; n = 128) groups and then subjected to a summer reproductive management program. Serum AMH was confirmed as a predictor of fertility measures (p < 0.05) in MH but not in the SH group. Cows were genotyped, which revealed four SNPs as predictive markers for serum AMH (p < 0.01), reproductive traits (p < 0.01), and additional physiological variables (p < 0.05). These SNPs were in the genes AMH, IGFBP1, LGR5, and TLR4. In conclusion, serum AMH concentrations and AMH polymorphisms are proposed as predictive markers that can be used in conjunction with genomic breeding value approaches to improve reproductive performance in Holstein cows exposed to summer HS conditions.

Examining the long-term impacts of ergot alkaloids on fetal heifer development and subsequent growth and reproductive performance

Consumption of toxic endophyte-infected tall fescue (EI) results in poor reproductive performance in domestic livestock. In this study, the objective was to evaluate the effects of ergovaline exposure during mid-gestation (days 93 through 188 of gestation) on dam performance, the growing female fetus, and the subsequent growth and reproductive performance of the gestationally exposed heifer calves. Pregnant Angus and Simmental-Angus cows were blocked by age (2 to 3, to 7, and >7 y), body weight (BW), and breed; and then randomly assigned to graze either novel endophyte-infected tall fescue (EN; <5% infection rate; n = 27 year 1, n = 16 year 2) or toxic EI (99% infection rate; n = 27 year 1, n = 17 year 2). Weekly BW, body condition scores (BCS), hair coat scores, hair shedding scores (HSS), and blood samples for progesterone (P4) analysis were collected from mid-April through July of 2017 (year 1) and 2018 (year 2). Gestation length, birth weight, placental characteristics, heifer calf growth, onset of puberty, ovarian characteristics, and artificial insemination pregnancy rates were measured. Data were analyzed using the MIXED procedure of SAS. Cows grazing EI pastures had reduced average daily gain, reduced BCS, greater HSS, and decreased P4 concentrations compared to cows on EN pasture (P < 0.01). Birth weights were decreased for heifers whose dams were exposed to EI pastures during their second trimester (P < 0.01). Heifer pregnancy rates were not impacted by EI pasture exposure during gestation for either year of the study. However, a treatment-by-year effect was seen for the pregnancy rate for EI-exposed heifers in year 2; EI-exposed heifers in year 2 had increased pregnancy rates at two of the inseminations. Combined, these data reinforce that consumption of toxic EI during gestation can negatively impact both dam and offspring performance. More studies are needed to evaluate more parameters in an effort to elucidate the possible life-long impacts of ergovaline exposure during gestation.

The moon cycle influences reproductive and productive traits in guinea pigs (Cavia porcellus) from a tropical Andean area

There is currently innumerable evidence showing that the lunar cycle affects various reproductive aspects in farm animals. However, there is very little information on the effect of the lunar cycle on productive traits in these species. A retrospective study was conducted (2015-2018) to evaluate the influence of the lunar cycle on some reproductive and productive traits in a guinea pig (Cavia porcellus) production system in the southern Andean region of Ecuador. A total of 7352 productive and reproductive records of guinea pig females housed in 3 m2 cages with a breeding male were analyzed. The following variables were considered: offspring sex ratio, litter size per cage, number of weaned guinea pigs, mortality, individual and litter weaning weight of guinea pigs, and calving frequency. The lunar cycle was split into eight periods of ~3.7-d length each. Data were analyzed by logistic regression and general linear model, and means were compared by the least mean squares method of the SAS. The offspring sex ratio was not correlated to the lunar cycle. The lunar cycle at mating and calving influenced the litter size per cage, number of weaned, and mortality of guinea pigs. The individual and litter-weaning weights were influenced by the lunar cycle at calving. The frequency of calving was greater around the new and full moon than in the remaining periods of the lunar cycle. In conclusion, the lunar cycle influenced several productive and reproductive traits in guinea pigs, such as litter size, mortality, number of pups weaned, and individual and litter weaning weights. This valuable information may have practical applications in management of guinea pig production systems.

Longitudinal genomic analyses of automatically-recorded vaginal temperature in lactating sows under heat stress conditions based on random regression models

BACKGROUND

Automatic and continuous recording of vaginal temperature (TV) using wearable sensors causes minimal disruptions to animal behavior and can generate data that enable the evaluation of temporal body temperature variation under heat stress (HS) conditions. However, the genetic basis of TV in lactating sows from a longitudinal perspective is still unknown. The objectives of this study were to define statistical models and estimate genetic parameters for TV in lactating sows using random regression models, and identify genomic regions and candidate genes associated with HS indicators derived from automatically-recorded TV.

RESULTS

Heritability estimates for TV ranged from 0.14 to 0.20 over time (throughout the day and measurement period) and from 0.09 to 0.18 along environmental gradients (EG, - 3.5 to 2.2, which correspond to dew point values from 14.87 to 28.19 ˚C). Repeatability estimates of TV over time and along EG ranged from 0.57 to 0.66 and from 0.54 to 0.77, respectively. TV measured from 12h00 to 16h00 had moderately high estimates of heritability (0.20) and repeatability (0.64), indicating that this period might be the most suitable for recording TV for genetic selection purposes. Significant genotype-by-environment interactions (GxE) were observed and the moderately high estimates of genetic correlations between pairs of extreme EG indicate potential re-ranking of selection candidates across EG. Two important genomic regions on chromosomes 10 (59.370-59.998 Mb) and16 (21.548-21.966 Mb) were identified. These regions harbor the genes CDC123, CAMK1d, SEC61A2, and NUDT5 that are associated with immunity, protein transport, and energy metabolism. Across the four time-periods, respectively 12, 13, 16, and 10 associated genomic regions across 14 chromosomes were identified for TV. For the three EG classes, respectively 18, 15, and 14 associated genomic windows were identified for TV, respectively. Each time-period and EG class had uniquely enriched genes with identified specific biological functions, including regulation of the nervous system, metabolism and hormone production.

CONCLUSIONS

TV is a heritable trait with substantial additive genetic variation and represents a promising indicator trait to select pigs for improved heat tolerance. Moderate GxE for TV exist, indicating potential re-ranking of selection candidates across EG. TV is a highly polygenic trait regulated by a complex interplay of physiological, cellular and behavioral mechanisms.

Review of the Heat Stress-Induced Responses in Dairy Cattle

In the dairy cattle sector, the evaluation of the effects induced by heat stress is still one of the most impactful and investigated aspects as it is strongly connected to both sustainability of the production and animal welfare. On the other hand, more recently, the possibility of collecting a large dataset made available by the increasing technology diffusion is paving the way for the application of advanced numerical techniques based on machine learning or big data approaches. In this scenario, driven by rapid change, there could be the risk of dispersing the relevant information represented by the physiological animal component, which should maintain the central role in the development of numerical models and tools. In light of this, the present literature review aims to consolidate and synthesize existing research on the physiological consequences of heat stress in dairy cattle. The present review provides, in a single document, an overview, as complete as possible, of the heat stress-induced responses in dairy cattle with the intent of filling the existing research gap for extracting the veterinary knowledge present in the literature and make it available for future applications also in different research fields.

A missense mutation (rs209302038) of KRT9 gene associated with heat stress in Chinese cattle

Type I keratin 9 encoded by the KRT9 gene serves an important special function either in the mature palmar and plantar skin tissue. The changes in skin conditions and thickening of the outer layer of the skin may be affected by environmental variables. A missense mutation rs209302038 (NC_037346.1: g.41782870 G > A) was detected in KRT9, which changing the isoleucine into valine. This study aimed to identify the frequency of allele in this locus in Chinese indigenous cattle, and analyze the connection with heat stress. Our results indicated that the frequency of allele A gradually decreases from south to north, while the frequency of G allele showed the opposite pattern. Further analysis of the association of the different genotypes with three climate factors, which showed that the genotypes (GG, GA, AA) were significantly related to climatic conditions (p < 0.01). Therefore, we speculated that the mutation of the rs209302038 in Chinese indigenous cattle might be a genetic marker to detect heat stress.

Effects of heat-stress-reducing systems on blood constituents, milk production and milk quality of Holstein and Jersey cows and heifers on pasture

The objective of this study was to evaluate the influence of different heat-stress-reducing systems, i.e., sprinkler + artificial shade, shower + artificial shade, and artificial shade, on serum mineral, hormonal, hematological, and metabolite profiles, on milk production, and milk composition in lactating cows and pubertal heifers of Holstein and Jersey breeds. For this purpose, 12 animals were used: 3 Holstein cows with an average (mean ± SD) body weight of 600 ± 30 kg, 53 ± 11 months of age, and milk yield of 27 ± 3.5 kg/day; 3 Jersey cows with an average body weight of 370 ± 11 kg, 40 ± 6 months of age, and milk production of 11 ± 1.5 kg/day; 3 Holstein heifers (325 ± 25 kg and 16 ± 0.6 months of age); and 3 Jersey heifers (250 ± 25 kg and 13 ± 0.6 months of age). Animals were used in a replicated 3 × 3 Latin square design with a 3 × 2 × 2 factorial arrangement of treatments that included three treatments (sprinkler + artificial shade, shower + artificial shade, and artificial shade), two breeds (Holstein, Jersey), and two physiological stages (lactating cows, heifers). The experimental treatments influenced (P < 0.05) the concentrations of triiodothyronine, with the shower and shade systems showing greater and similar concentrations (99.5 and 96.3 µg/dL, respectively) when compared with sprinkler treatment (89.2 µg/dL). There was an effect (P < 0.05) of breed on the concentrations of Na + , K + , hemoglobin, hematocrit and mean corpuscular volume levels with the Holsteins having lower levels of Na + , K + , hemoglobin, hematocrit and mean corpuscular volume (101.1, 4.0 ng/mL, 11.2 g/dL, 24.7%, and 42.3 μm3, respectively) than the Jerseys (106.5 and 4.3 ng/mL, 12.4 g/dL, 27.7%, and 46.3 μm3, respectively. Total cholesterol and high-density lipoproteins were influenced by physiological stage (P < 0.05). Concentrations of cholesterol and high-density lipoproteins were higher for cows (94.1, and 56.9 mg/dL, respectively) than for heifers (56.9 and 42,9 mf/dL, respectively). Milk production and fat content were affected (P < 0.05) by breed (P < 0.05), with Holstein cows producing more milk (23.9 kg/day) than Jersey cows (12.0 kg/day), but Jersey cows had higher fat concentration (4.6%) than Holstein cows (3.0%). Therefore, the three different thermal-stress-reducing-systems tested were able to maintain the serum biomarkers within normal physiological ranges. However, the most appropriate thermal-stress-reducing-systems would be a sprinkler systema because it uses less water compared with the shower system.

Effect of shading on the physiological and reproductive parameters in Nelore cows

This study aimed to evaluate the physiological and reproductive parameters of Nelore cows under various microclimatic conditions. The experiment was performed in Central Brazil, which has a tropical climate with dry winters and rainy summers. The experimental groups were divided into an area with shading (5.8 trees/ha; n = 42) and an area with little shading (0.4 trees/ha; n = 42). The physiological (heart rate, respiratory rate, rectal temperature, surface body temperature, and vaginal temperature) and reproductive (estrus detection, conception rate, and rate of pregnancy loss) parameters were then assessed. The rectal temperature (p = 0.002); surface body temperature on the flanks, forehead, and shoulder (p < 0.001); and vaginal temperature (p < 0.001) of cows in the group with shading were significantly lower than those of cows in the group without shading. Estrus was higher (p = 0.08) in the shaded group; however, no effect was observed on conception and pregnancy loss rates. In conclusion, shading (5.8 trees/ha) provided better thermal comfort for Nelore animals in the tropical climatic region. However, this did not affect their performance after fixed-time artificial insemination.

Seasonal distribution of repeat breeder cows and evaluation of modified protocols for post AI treatment during summer

An important problem of dairy industry worldwide is repeat breeder cows (RB). In this study, one farm in Northern Greece was chosen on the basis of subfertility. First, the available reproductive data of the previous year were evaluated; then, the farmer was advised to use the most common treatments for RB [GnRH with the third artificial insemination (AI+GnRH) or ovsynch in cows found empty after the second AI], and their efficacy was monitored throughout the year. Cows (n = 147) 2.5 to 4.5 years old were included. During the next year, post AI treatments (meta-ovsynch and meta-AI) were used during summer; GnRH (100 μg of gonadorelin) alone or in combination with meloxicam (0.5 mg/kg BW) was used during summer. Meta-ovsynch protocols were administered to 29 cows detected as non-pregnant after 3 AIs; cows were divided randomly into 3 meta-ovsynch (OS) groups: group OS (controls, n = 10), standard ovsynch protocol; group OS+GnRH (n = 10), OS plus GnRH 10 days after AI; and group OS+GnRH+NSAID (n = 9), OS plus GnRH 10 days after AI plus meloxicam 15 days after AI. Meta-AI protocols were tested in 27 RB cows; cows were divided randomly into 3 AI groups: GnRH (n = 9), 1 dose of GnRH with AI; GnRH-GnRH (n = 9), two doses of GnRH, one with AI and another 10 days later; and GnRH-GnRH-NSAID (n = 9), two doses of GnRH as in GnRH-GnRH group and one dose of meloxicam 15 days after AI. Pregnancy diagnosis was performed by ultrasound 38 days after AI. During the 1st year of evaluation, 53.79% of cows had received ≥ 3 AIs; the highest percentage (38.48%) of RB cows was recorded during autumn. After treatment for RB, the lowest (P < 0.05) pregnancy rate (PR) was recorded in August (18.18%) compared to January (75.0%), May (53.33%), and December (50.0%, P < 0.1). The efficacy of ovsynch during winter was significantly higher compared to all the other seasons. The percentage of cows with increased estrous cycle duration (24-37 days) after RB treatment and AI was the highest (P < 0.05) in spring and summer after AI+GnRH and the lowest (P < 0.05) during winter after ovsynch. Concerning the post AI treatments during summer, significantly higher pregnancy rate was recorded in the OS+GnRH+NSAID group (55.55%) compared to OS+GnRH (10%) and OS (10%) groups. Pregnancy rates did not differ among AI groups. It seems that OS+GnRH+NSAID is a promising protocol for RB cows during summer although further research is needed to support the present results.

The Effect of Month and District on 100-Day In-Calf Rate in Year-Round Calving Dairy Herds

Monitoring 100-day in-calf rate (100DICR) is an integral part of the assessment of reproductive performance in year-round calving dairy herds. The objective of this study was to investigate the effect of month on 100DICR in year-round calving herds in New South Wales (NSW), Australia and determine whether a fluctuating 100DICR target is an appropriate alternative to a constant 100DICR target. The 100DICR is defined as the percentage of all current lactating cows over 100 days in milk (DIM) that conceive on or before 100 DIM. As dairy cows are typically dried off 7 months after conception, 100DICR was an approximate 7-month rolling average. Mean monthly 100DICRs were calculated with a generalised linear model for six NSW north coast herds located 15-140 km from the coast and four NSW south coast herds located less than 10 km from the coast, over a two-year period. The mean 100DICR was lowest in May at 28.62% (95%CI 28.31-28.93) and increased during winter and spring, peaking in December at 34.74% (95%CI 34.32-35.15). The observed trend was similar for north and south coast herds, although north coast herds experienced a greater change in 100DICR from the peak to a nadir of 27.58% (95%CI 27.18-27.98), a 7.15-point difference, compared to south coast herds with a nadir of 30.18% (95%CI 29.69-30.67), a 4.67-point difference between the peak and nadir. In conclusion, 100DICR is affected by month with the lowest 100DICRs observed in late autumn and the highest 100DICRs observed in late spring and early summer. Therefore, a fluctuating target 100DICR is an appropriate alternative to a constant target when assessing reproductive performance in year-round calving herds. While the district does not affect mean 100DICR per se, the district does affect the difference between peak and nadir 100DICR.

Transgenerational transmission of environmental effects in livestock in the age of global warming

Recent decades provide mounting evidence for the continual increase in global temperatures, now termed "global warming," to the point of drastic worldwide change in the climate. Climatic change is a long-term shift in temperatures and weather patterns, including increased frequency and intensity of extreme environmental events such as heat waves accompanied by extreme temperatures and high humidity. Climate change and global warming put several challenges to the livestock industry by directly affecting the animal's production, reproduction, health, and welfare. The broad impact of global warming, and in particular heat stress, on-farm animals' performance has been comprehensively studied. It has been estimated that the US livestock industry's loss caused by heat stress is up to $2.4 billion annually. However, the long-term intergenerational and transgenerational effects of climatic change and global warming on farm animals are sparse. Transgenerational effects, which are mediated by epigenetic mechanisms, can affect the animal's performance regardless of its immediate environment by altering its phenotypic expression to fit its ancestors' environment. In many animal species, environmental effects are epigenetically encoded within a narrow time interval during the organism's gametogenesis, and these epigenetic modifications can then be intergenerationally transmitted. Several epigenetic mechanisms mediate intergenerational transmission of environmental effects, typically in a parent-dependent manner. Therefore, exposure of the animal to an extreme climatic event and other environmental stressors during gametogenesis can undergo epigenetic stabilization in the germline and be passed to the offspring. As a result, the offspring might express a phenotype adjusted to fit the stressors experienced by their ancestors, regardless of their direct environment. The purpose of this perspective is to review current evidence for intergenerational and transgenerational transmission of environmental stress effects, specifically in the context of global warming and climate change, and to offer viewpoints on the possible impacts on the livestock industry.

The Effect of Month of Harvesting and Temperature-Humidity Index on the Number and Quality of Oocytes and In Vitro Embryo Production in Holstein Cows and Heifers

The aim of this study was to evaluate the effect of the month of oocyte harvesting and the temperature-humidity index on oocyte number and quality harvested from Holstein cows and heifers, oocyte developmental competence, and total embryos produced in an area of intense ambient temperature for most of the year. A total of 5064 multiparous lactating cows and 2988 nulliparous heifers were used as oocyte donors and distributed across the months of the year. Overall, total oocytes per collection did not differ (p > 0.05) between cows (16.6 ± 2.7) and heifers (15.1 ± 1.8), but oocyte developmental competence was lower (p < 0.05) in cows (21.3 ± 5.4) than heifers (25.5 ± 4.0). For cows, the total number of oocytes harvested was two-fold higher (p < 0.05) in November than in May. For heifers, the total number of oocytes harvested was highest in April (17.19 ± 0.53) and lowest in May (10.94 ± 0.32; p < 0.05). For cows, total embryos were highest in November (2.58 ± 0.42) and lowest in August (1.28 ± 0.10; p < 0.05). Thus, taken together, these results indicate that severe heat stress impaired the number and quality of oocytes harvested from donor Holstein multiparous cows and heifers, oocyte developmental competence, and total embryos produced in this area of intense ambient temperature for most of the year.

Heat Stress as a Barrier to Successful Reproduction and Potential Alleviation Strategies in Cattle

In recent decades, the adverse effects of global warming on all living beings have been unanimously recognized across the world. A high environmental temperature that increases the respiration and rectal temperature of cattle is called heat stress (HS), and it can affect both male and female reproductive functions. For successful reproduction and fertilization, mature and healthy oocytes are crucial; however, HS reduces the developmental competence of oocytes, which compromises reproduction. HS disturbs the hormonal balance that plays a crucial role in successful reproduction, particularly in reducing the luteinizing hormone and progesterone levels, which leads to severe problems such as poor follicle development with a poor-quality oocyte and problems related to maturity, silent estrus, abnormal or weak embryo development, and pregnancy loss, resulting in a declining reproduction rate and losses for the cattle industry. Lactating cattle are particularly susceptible to HS and, hence, their reproduction rate is substantially reduced. Additionally, bulls are also affected by HS; during summer, semen quality and sperm motility decline, leading to compromised reproduction. In summer, the conception rate is reduced by 20-30% worldwide. Although various techniques, such as the provision of water sprinklers, shade, and air conditioning, are used during summer, these methods are insufficient to recover the normal reproduction rate and, therefore, special attention is needed to improve reproductive efficiency and minimize the detrimental effect of HS on cattle during summer. The application of advanced reproductive technologies such as the production of embryos in vitro, cryopreservation during the hot season, embryo transfer, and timed artificial insemination may minimize the detrimental effects of HS on livestock reproduction and recover the losses in the cattle industry.

Dual-Purpose Cattle Raised in Tropical Conditions: What Are Their Shortcomings in Sound Productive and Reproductive Function?

Dual-purpose husbandry might well be the most commonly employed cattle management system in tropical regions worldwide. The advantages of producing both meat and milk, although in reduced quantities, gives an edge to the farmer in coping with the volatile economic conditions that prevail in the region. Herein, we discuss the different methods of cattle management under tropical conditions based on the financial and social structure of this system. An account of the sanitary and nutritional conditions available to the farmers and how these factors affect the profitability of the enterprise will also be given. Finally, we will discuss how these systems can take advantage of several biotechnological procedures, and how these tools (such as controlled natural mating, artificial insemination, and embryo transfer) affect reproductive outcomes. The present review will mainly concentrate on production systems located less than 1000 m above sea level, as the problems and shortcomings of cattle raised above this arbitrary landmark are quite different.

Effect of Genetic and Environmental Factors on Twin Pregnancy in Primiparous Dairy Cows

Twin pregnancies are highly undesirable in dairy cattle; they compromise the health and wellbeing of a cow and dramatically impair the farm economy. Recently, a genomic prediction for twin pregnancies has been developed. The objective of this study was to assess environmental and management risk factors affecting the incidence of twin pregnancies in high-producing dairy cows in their first lactation, with a special emphasis placed on the genomic prediction values of twin pregnancy. Our study population of primiparous cows proved valuable in identifying factors other than genomic predictive values that influence twin pregnancy rates. The odds ratio for twin pregnancies was 0.85 (p < 0.0001) for each unit of a prediction value increase, 3.5 (p = 0.023) for cows becoming pregnant during the negative photoperiod, and 0.33 (p = 0.016) for cows producing ≥42 kg of milk at AI, compared with the remaining cows who produced <42 kg of milk. As a general conclusion, the practical implication of our findings is that genomic prediction values can identify the risk of twin pregnancy at a herd level. Given the cumulative effect of genomic selection, selecting animals with a reduced genetic risk of twin pregnancies can contribute to reducing the incidence of twin pregnancies in dairy herds.

Heat Stress: A Serious Disruptor of the Reproductive Physiology of Dairy Cows

Global warming is a significant threat to the sustainability and profitability of the dairy sector, not only in tropical or subtropical regions but also in temperate zones where extreme summer temperatures have become a new and challenging reality. Prolonged exposure of dairy cows to high temperatures compromises animal welfare, increases morbidity, and suppresses fertility, resulting in devastating economic losses for farmers. To counteract the deleterious effects of heat stress, cattl e employ various adaptive thermoregulatory mechanisms including molecular, endocrine, physiological, and behavioral responses. These adaptations involve the immediate secretion of heat shock proteins and cortisol, followed by a complex network of disrupted secretion of metabolic and reproductive hormones such as prolactin, ghrelin, ovarian steroid, and pituitary gonadotrophins. While the strategic heat stress mitigation measures can restore milk production through modifications of the microclimate and nutritional interventions, the summer fertility records remain at low levels compared to those of the thermoneutral periods of the year. This is because sustainment of high fertility is a multifaceted process that requires appropriate energy balance, undisrupted mode of various hormones secretion to sustain the maturation and fertilizing competence of the oocyte, the normal development of the early embryo and unhampered maternal-embryo crosstalk. In this review, we summarize the major molecular and endocrine responses to elevated temperatures in dairy cows, as well as the impacts on maturing oocytes and early embryos, and discuss the consequences that heat stress brings about in dairy cattle fertility.

Granulosa cell-derived extracellular vesicles mitigate the detrimental impact of thermal stress on bovine oocytes and embryos

Climate change-induced global warming results in rises in body temperatures above normal physiological levels (hyperthermia) with negative impacts on reproductive function in dairy and beef animals. Extracellular vesicles (EVs), commonly described as nano-sized, lipid-enclosed complexes, harnessed with a plethora of bioactive cargoes (RNAs, proteins, and lipids), are crucial to regulating processes like folliculogenesis and the initiation of different signaling pathways. The beneficial role of follicular fluid-derived EVs in inducing thermotolerance to oocytes during in vitro maturation (IVM) has been evidenced. Here we aimed to determine the capacity of in vitro cultured granulosa cell-derived EVs (GC-EVs) to modulate bovine oocytes’ thermotolerance to heat stress (HS) during IVM. Moreover, this study tested the hypothesis that EVs released from thermally stressed GCs (S-EVs) shuttle protective messages to provide protection against subsequent HS in bovine oocytes. For this, sub-populations of GC-EVs were generated from GCs subjected to 38.5°C (N-EVs) or 42°C (S-EVs) and supplemented to cumulus-oocyte complexes (COCs) matured in vitro at the normal physiological body temperature of the cow (38.5°C) or HS (41°C) conditions. Results indicate that S-EVs improve the survival of oocytes by reducing ROS accumulation, improving mitochondrial function, and suppressing the expression of stress-associated genes thereby reducing the severity of HS on oocytes. Moreover, our findings indicate a carryover impact from the addition of GC-EVs during oocyte maturation in the development to the blastocyst stage with enhanced viability.

Replacement of the first GnRH by estradiol in the breeding Ovsynch of Double Ovsynch protocol could improve fertility in Holstein dairy cows

Unlike GnRH, estradiol could induce emergence of a new follicular wave regardless of the size of follicle. Therefore, the present study was conducted to understand whether replacement of the first GnRH by estradiol in the breeding protocol of Double Ovsynch program could enhance fertility. Cows were randomly assigned to two groups, including Double Ovsynch protocol (Control; n = 120) and Ovsynch-estradiol-PGF2α-GnRH (EPG) protocol (Treatment; n = 120). Cows in both groups were subjected to presynchronization Ovsynch. Seven days later, cows in the control group received GnRH, which was followed by PGF2α and GnRH 7 days and 9 days plus 8 h later, respectively. Cows in treatment group received estradiol 7 days after the second GnRH of presynchronization Ovsynch, which was followed by PGF2α and GnRH 7 days and 10 days plus 8 h later, respectively. Cows were subjected to timed AI (TAI) 16 h after final GnRH in both groups. Pregnancy per AI (P/AI) was greater in cows in treatment than control group (64.17 % vs. 44.17 %, respectively; P = 0.02). Cows with a follicle with diameter ≥ 10 mm (F10) at the beginning of EPG in treatment group had greater P/AI than cows without a F10 at the beginning of breeding Ovsynch in control group (P ≤ 0.05). Pregnancy per AI was greater in cows with a CL at the beginning of EPG in treatment group than cows without a CL at the same timepoint in treatment group, and cows with or without a CL at the beginning of breeding Ovsynch in control group (P ≤ 0.05). In conclusion, inclusion of estradiol in Double Ovsynch protocol as a replacement for the first GnRH of breeding Ovsynch could improve fertility, particularly in cows with a CL at the initiation of EPG.

Animal welfare and effects of per-female stress on male and cattle reproduction—A review

Thermal stress causes severe effects on the wellbeing and reproduction of cattle, including changes in oogenesis and spermatogenesis, generating great concerns, which last for decades. In cattle, the occurrence of thermal stress is associated with a reduction in the production of spermatozoids and ovarian follicles, in addition to the increase of major and minor defects in gametes or in their intermediate stages. In bovine females able to reproduce, a reduction in the rate of estrus manifestation and an increase in embryonic mortality has been observed. Therefore, keeping animals on good welfare conditions, with water supply and in shaded areas can favor the improvement of different reproductive parameters. For all this, the present study aimed to gather, synthesize and argue recent studies related to animal welfare, focusing on the effects of thermal stress on the reproduction of cattle, aiming to support possible strategies to mitigate the harmful effects of thermal stress in this species.

Repeat breeding: prevalence and potential causes in dairy cows at different milk pocket areas of Bangladesh

The objective of this study was to figure out the prevalence and probable causes of repeat breeding (RB) in dairy cows. Hence, a cross-sectional study was conducted on randomly selected 265 dairy farms in Sirajganj, Bogura, Rangpur, Satkhira, and Munshiganj districts of Bangladesh from December 2018 to February 2019. Data were collected through a direct interview method using a survey questionnaire. The reproductive organs of repeat breeder cows were examined for pathological, infectious, and functional reasons, and genital tract abnormalities. Additionally, the influence of nutrition, season, and age on the frequency of RB was recorded. The prevalence of RB was 28% among the 3824 cows investigated. Among the total repeat breeder cases, 72.54% of RB cases were found in Holstein-Friesian crossbred, 23.90% in Jersey crossbred, 1.50% in Sahiwal crossbred, and 2.06% in indigenous cows. The prevalence of RB was significantly highest (P < 0.01) in Satkhira (44.35%) and lowest in the Munshiganj district (15.87%). Data indicated that a major proportion of cows significantly (P < 0.05) faced RB problems due to functional causes (34.18%), followed by pathological causes (28.01%), genital tract abnormalities (21.32%), and infectious causes (16.49%). Furthermore, the cows were remarkably (P < 0.001) affected in RB during the summer season and nutritional deficient diseases like milk fever (70%). Age (3-7 years) had a significant (P < 0.001) effect on the RB occurrence (90%) in crossbred cows. However, particular focus should be given to systematic breeding, balanced nutrition, artificial inseminator efficiency, and hygienic inseminating tools to reduce RB incidence in high-yielding crossbred cows.

Effects of Heat Stress in Dairy Cows Raised in the Confined System: A Scientometric Review

Due to climate change, heat stress is a growing problem for the dairy industry. Based on this, annual economic losses in the dairy sector are verified mainly on a large scale. Despite several publications on thermal stress in lactating dairy cows in confinement systems, there need to be published reviews addressing this issue systematically. Our objective was to scientometrically analyze the effects of heat stress in dairy cows managed in a confinement system. Based on PRISMA guidelines, research articles were identified, screened, and summarized based on inclusion criteria for heat stress in a confinement system. Data was obtained from the Web of Science. A total of 604 scientific articles published between 2000 and April 2022 were considered. Data was then analyzed using Microsoft Excel and CiteSpace. The results pointed to a significant increase in studies on heat stress in lactating cows housed in confinement systems. The main research areas were Agriculture, Dairy Animal Science and Veterinary Sciences. The USA showed the highest concentration of studies (31.12%), followed by China (14.90%). Emerging themes included heat stress and behavior. The most influential journals were the Journal of Dairy Science and the Journal of Animal Science. The top authors were L. H. Baumgard and R. J. Collier. The leading institutions were the Chinese Academy of Agricultural Sciences, followed by the State University System of Florida and the University of Florida. The study maps the significant research domains on heat stress of lactating cows in confinement systems, discusses implications and explanations and highlights emerging trends.

Genetic diversity and thermotolerance in Holstein cows: Pathway analysis and marker development using whole-genome sequencing

Heat stress causes extensive losses in the dairy sector, due to negative effects on milk production and reproduction. Cows have evolved a series of protective mechanisms, (physiological, biochemical, behavioural) to cope with the thermostressing environments, which have allowed the preservation of productive and reproductive potential of specific animals during summer; these animals are considered thermotolerant and could be used to design programs of selective breeding. These programs, targeting the generations of a population of heat-resistant animals, would increase the frequency of the desired phenotypes, tackling the financial losses on one hand and reducing the carbon footprints of the dairy sector on the other. The development of genomics techniques has enabled genome wide variant calling, to detect SNPs associated with the desired phenotypes. In this study, we used a comparative genomics approach to detect genetic variation associated with thermotolerance and to design molecular markers for characterizing the animals as tolerant/sensitive. A total of 40 cows from each group were split in four sequencing pools and a whole-genome sequencing approach was used. Results and conclusion: Genome-wide genetic variation between groups was characterized and enrichment analysis revealed specific pathways which participate in the adaptive mechanisms of thermotolerance, implicated into systemic and cellular responses, including the immune system functionality, Heat Stress and Unfolded Protein Response. The markers made a promising set of results, as specific SNPs in five genes encoding for Heat Shock Proteins were significantly associated with thermotolerance.

Fertility of Holstein cows and heifers submitted to timed artificial insemination and receiving one or two doses (12 h apart) of semen

The objective of this retrospective study was to assess the effect of receiving a single (n = 50,285) or double (n = 4392) artificial insemination (AI), 12 h apart, within a timed artificial insemination protocol on pregnancy per AI (P/AI) in nulliparous heifers (inseminated with either sex-sorted or conventional semen) and pluriparous Holstein cows in a commercial dairy herd. Also, this study aimed to investigate the relationship between temperature-humidity index (THI) and time of the first AI and fertility. Fertility of cows receiving two AI with normothermia (THI <68) was higher (p < .05) than cows receiving a single AI (42.9% vs. 36.4%). P/AI of cows receiving two AI with severe heat stress (THI >85) was higher (p < .05) than cows receiving a single AI (21.0% vs. 12.6%). Regardless of heat stress conditions, applying the first AI in the morning increased (p < .05) P/AI in cows with double AI than in cows whose first AI occurred in the afternoon (38.4 vs. 33.3%). With moderate heat stress, and sexed-sorted semen, P/AI to timed AI was higher (65.0 vs. 51.9%; p < .05) in heifers receiving double AI than those serviced once. It was concluded that double AI, 12 h apart, enhanced fertility at timed AI than herd mates with a single AI, particularly with heat stress at breeding.

The Impact of Heat Stress on Immune Status of Dairy Cattle and Strategies to Ameliorate the Negative Effects

Heat stress (HS) is well known to influence animal health and livestock productivity negatively. Heat stress is a multi-billion-dollar global problem. It impairs animal performance during summer when animals are exposed to high ambient temperatures, direct and indirect solar radiations, and humidity. While significant developments have been achieved over the last few decades to mitigate the negative impact of HS, such as physical modification of the environment to protect the animals from direct heat, HS remains a significant challenge for the dairy industry compromising dairy cattle health and welfare. In such a scenario, it is essential to have a thorough understanding of how the immune system of dairy cattle responds to HS and identify the variable responses among the animals. This understanding could help to identify heat-resilient dairy animals for breeding and may lead to the development of climate resilient breeds in the future to support sustainable dairy cattle production. There are sufficient data demonstrating the impact of increased temperature and humidity on endocrine responses to HS in dairy cattle, especially changes in concentration of hormones like prolactin and cortisol, which also provide an indication of the likely im-pact on the immune system. In this paper, we review the recent research on the impact of HS on immunity of calves during early life to adult lactating and dry cows. Additionally, different strategies for amelioration of negative effects of HS have been presented.

Programming effects of late gestation heat stress in dairy cattle

The final weeks of gestation represent a critical period for dairy cows that can determine the success of the subsequent lactation. Many physiological changes take place and additional exogenous stressors can alter the success of the transition into lactation. Moreover, this phase is pivotal for the final stage of intrauterine development of the fetus, which can have negative long-lasting postnatal effects. Heat stress is widely recognised as a threat to dairy cattle welfare, health, and productivity. Specifically, late gestation heat stress impairs the dam's productivity by undermining mammary gland remodelling during the dry period and altering metabolic and immune responses in early lactation. Heat stress also affects placental development and function, with relevant consequences on fetal development and programming. In utero heat stressed newborns have reduced birth weight, growth, and compromised passive immune transfer. Moreover, the liver and mammary DNA of in utero heat stressed calves show a clear divergence in the pattern of methylation relative to that of in utero cooled calves. These alterations in gene regulation might result in depressed immune function, as well as altered thermoregulation, hepatic metabolism, and mammary development jeopardising their survival in the herd and productivity. Furthermore, late gestation heat stress appears to exert multigenerational effects, influencing milk yield and survival up to the third generation.

Inhibition of Hsp90 during in vitro maturation under thermoneutral or heat shock conditions compromises the developmental competence of bovine oocytes

Heat shock protein 90 (Hsp90) is critical for cell homeostasis but its role on bovine oocyte maturation is not well known. We investigated the importance of Hsp90 for competence of bovine oocyte using 17-(allylamino)-17-demethoxygeldanamycin (17AAG), an inhibitor of Hsp90, during in vitro maturation (IVM). Three experiments evaluated the effect of 17AAG on developmental competence of oocytes matured in vitro under thermoneutral (38.5ºC) or heat shock (HS; 41.5ºC) temperatures. The first experiment found that the blastocyst rates were lower (P < 0.05) with 2 µM 17AAG compared with the untreated control (0 µM). The abundance of HSF1 transcripts was higher in oocytes matured with 2 µM than with 0 and 1 µM 17AAG, whereas the abundance of HSP90AA1 and HSPA1A transcripts was lower (P < 0.05) with 1 and 2 µM than with 0 µM. The second experiment found that 2 µM 17AAG for 12 or 24 h during IVM decreased (P < 0.05) the blastocysts rates. In the third experiment, the association of 2 μM 17AAG with HS for 12 h during IVM resulted in lower (P < 0.05) blastocysts rates than 17AAG, HS or untreated control. In conclusion, inhibition of Hsp90 during in vitro maturation compromises further embryo development; the association of Hsp90 inhibition with HS aggravates the deleterious effect of both on oocyte developmental competence.

Behavior and thermal comfort of light and dark coat dairy cows in the Eastern Amazon

This study aimed to evaluate the behavior and thermal comfort of 20 Girolando cows (5/8-H/G), with light and dark coats, in the wettest period of the year, in Santarém, Pará, Brazil, in pasture with access to shade, and plenty of drinking water and mineral salt. Animal behavior categories were computed for 12 h a day, on 3 days in a row, by trained observers. Three day shifts were considered: Morning (6:00 a.m. to 9:55 a.m.), Intermediate (10:00 a.m. to 01:55 p.m.) and Afternoon (2:00 p.m. to 05:55 p.m.). The Temperature Index (TI), the Black Globe Humidity Index (BGHI) and the Comfort Index (CI) were calculated to measure thermal comfort. At all times studied, BGHI pointed that the environment was outside the thermal comfort zone. Dark-coated animals spent more 34.26% of the time in activities in the shade. The light-coated animals remained more 11.88% of the time in the sun, performing their natural behaviors. Both light and dark coat animals remained more 77 and 74.44% of the time in the sun, respectively. The behavior “in the sun while grazing” was the most evident, in both coats, in the studied shifts. The behaviors “in the shade while walking” and “in the shade while standing idle” were more evident (p < 0.01) in dark-coated cattle. The grazing behavior was higher in animals with dark coat (p < 0.05). In all evaluated shifts, there was a positive correlation between the behavior “in the sun while grazing” with the CI (r = 0.44211; p < 0.0305). Behaviors performed in the shade, such as “idleness while lying down,” “ruminating while lying down and standing up,” and behaviors “in the sun,” “idleness while lying down” and “ruminating while lying down,” were negatively correlated with CI. It is concluded that, even in the wettest period of the year, in the Eastern Amazon, Girolando dairy cows are exposed to hot environments, which causes thermal discomfort and changes in their natural behavior, as they spend more time standing in shaded areas, usually in rumination. Also, light-coated cows spend more time in the sun, while dark-coated cows spend more time in the shade. Thus, light-coated cows tend to have health and zootechnical performance negatively affected.

Influence of Different Heat-Stress-Reducing Systems on Physiological and Behavioral Responses and Social Dominance of Holstein and Jersey Cows and Heifers on Pasture

High ambient temperatures and relative humidity affect the behavior and physiology of the animal. This study investigated the influence of different heat-stress-reducing systems on the physiological, behavioral, and preferential responses of Holstein and Jersey cows and heifers on pasture. Experimental treatments were: (1) three heat-stress-reducing systems (sprinklers + artificial shade; showers + artificial shade; and artificial shade); (2) two breeds (Holstein and Jersey); and (3) two physiological stages (lactating cows and pubertal heifers). Physiological and behavioral responses to treatments were measured every 30 min on collection days. The frequency and duration of the use of the systems were recorded continuously 24 h/day for 3 days in each period. The air temperature and the relative humidity were 26 ± 4.1 °C and 74 ± 11.3%, respectively. The experimental treatments affected (p = 0.0354) standing idle, grazing behavior (p = 0.0435), and the frequency and duration of use of the systems by the animals (p < 0.0001). For all treatments, the respiratory rate and the coat surface temperature were highly and significantly correlated (p < 0.05) with the temperature and humidity index. In conclusion, under ambient conditions, dairy cows preferred using sprinklers or showers over artificial shade. These systems were more efficient at reducing the heat load and led to better behavioral and physiological responses.

Effect of Folic Acid Supplements on Progesterone Profile and Blood Metabolites of Heat-Stressed Holstein Cows during the Early Stage of Pregnancy

The aim was to elucidate the impact of oral folic acid (FA) supplements on progesterone profile, blood metabolites and biochemical indices of heat-stressed Holstein cows during the early stage of pregnancy. The study lasted from the day of artificial insemination through the end of the fourth week of pregnancy. The first group (CON, n = 17) received 0 μg of FA/kg BW as a control. The second and third groups received oral FA doses of 5 (FA5, n = 19) and 10 (FA10, n = 20) μg kg−1 BW, respectively. At the 2nd and 3rd weeks of pregnancy, the FA10 group had greater progesterone levels than the CON group (p < 0.05). The FA10 group had a greater progesterone level than the FA5 and CON groups at the fourth week of pregnancy (p < 0.01). The FA10 group had higher folate levels than CON group during the first three weeks of pregnancy (p < 0.01). Both FA-supplemented groups had significantly greater serum folates than the CON group by the end of the fourth week of pregnancy (p < 0.01). At the 2nd and 4th weeks of pregnancy, the FA10 group had greater levels of serum glucose and globulin than the CON group (p = 0.028 and 0.049, respectively). Both FA-supplemented groups had greater serum growth hormone (GH) levels at the 4th week of pregnancy (p = 0.020). Additionally, the FA10 group showed significantly higher levels of IGF-1 at the 2nd and 4th week of gestation (p = 0.040 and 0.001, respectively). FA supplementation decreased the levels of non-esterified fatty acid (NEFA) at the 2nd and 4th week of gestation (p = 0.020 and 0.035, respectively). Additionally, the FA10 group showed significantly higher pregnancy-associated glycoprotein (PAG) levels at the 2nd and 4th week of gestation (p = 0.005 and 0.001, respectively). In conclusion, oral FA supplementation (10 mcg kg−1) in the first month of gestation improved the progesterone profile, as well as blood folates, PAG, GH, and IGF-1 concentrations in heat-stressed Holstein cows. These findings could be useful in developing practical strategies to keep dairy cows’ regular reproductive patterns under heat stress conditions.

Economic losses in dairy farms due to heat stress in sub-tropics: evidence from North Indian Plains

The present study assesses the sensitivity of dairy animals to thermal stress, and projects the economic losses due to heat stress in the Trans and Upper Gangetic plains region of India with Representative Concentration Pathway (RCP) 4.5 climate scenario for the time slice 2010-2039 and two subperiods, 2020-2029 and 2030-2039. The projections were carried out for two different scenarios of population and productivity growth of dairy animals, Business-as-Usual (BAU) and Alternate, whereby land, feed and fodder constraints were applied. The potential annual loss in milk production due to heat stress in the region was estimated to be around 361 and 377 thousand tons for the time slice 2010-2039 under BAU and Alternate scenario, respectively. In economic terms these losses, at current prices, would be equivalent to INR 11.93 billion and INR 12.44 billion, respectively. This gives an indication of the level of financial investment that can be made in adaptation measures to arrest the loss due to climate change.

Progesterone supplementation to improve fertility of selected subgroups of lactating cows during the summer and fall

One major cause of low fertility of cows in the summer is progesterone deficiency. We found that insertion of a controlled intravaginal drug-releasing (CIDR) device containing progesterone after artificial insemination (AI) increases pregnancy per AI (P/AI) in cows with uterine disease and low body condition score after calving. Here we treated only these two subgroups, during the summer and autumn. Control (n = 191 AI) and treatment (n = 230 AI) cows were inseminated at estrus and the treated group received a CIDR device on day 5 post-AI, for 14 days. Overall analysis of data during the summer and autumn indicated no significant differences between treatment and control groups. Analysis of the summer data only indicated a significant effect of treatment: P/AI was higher in CIDR-treated vs. control groups (34.2 vs. 19.3%; P < 0.038). Results indicated a 15% increase in P/AI during the summer for CIDR-treated cows in subgroups that had responded positively to the progesterone treatment.

Influence of PMSG on Superstimulation and Embryo Development Following Somatic Cell Nuclear Transfer in Holstein Cows in the United Arab Emirates

The present study investigated the effect of superstimulation to improve in vitro embryo production in the Gulf area, where the temperature is high. Holstein cows were classified into the control and superstimulation groups. Superstimulation was induced with a single intramuscular injection of pregnant mare serum gonadotropin (PMSG; 2500 IU) on day 14 of the estrus cycle (day 0; estrus). The development of follicles was evaluated by ultrasonography of the ovaries daily. At 40 h after the PMSG injection, oocytes were collected by the ovum pick-up (OPU) technique. OPU was performed at the same stage of the estrus cycle in the control group as in the superstimulation group. The number of follicles with a diameter of more than 6 mm and the number of retrieved cumulus-oocyte complexes were significantly higher in the superstimulation group than in the control group. Furthermore, the maturation rate was higher in the superstimulation group than in the control group. Cloned embryos were produced by somatic cell nuclear transfer using matured oocytes. The cleavage and blastocyst formation rates were significantly higher in the superstimulation group than in the control group. In conclusion, a single injection of PMSG can facilitate the efficient production of cloned cow embryos.

Transcriptome Reveals Granulosa Cells Coping through Redox, Inflammatory and Metabolic Mechanisms under Acute Heat Stress

Heat stress affects granulosa cells (GCs) and the ovarian follicular microenvironment, causing poor oocyte developmental competence and fertility. This study aimed to investigate the physical responses and global transcriptomic changes in bovine GCs to acute heat stress (43 °C for 2 h) in vitro. Heat-stressed GCs exhibited transient proliferation senescence and resumed proliferation at 48 h post-stress, while post-stress immediate culture-media change had a relatively positive effect on proliferation resumption. Increased accumulation of reactive oxygen species and apoptosis was observed in the heat-stress group. In spite of the upregulation of inflammatory (CYCS, TLR2, TLR4, IL6, etc.), pro-apoptotic (BAD, BAX, TNFSF9, MAP3K7, TNFRSF6B, FADD, TRADD, RIPK3, etc.) and caspase executioner genes (CASP3, CASP8, CASP9), antioxidants and anti-apoptotic genes (HMOX1, NOS2, CAT, SOD, BCL2L1, GPX4, etc.) were also upregulated in heat-stressed GCs. Progesterone and estrogen hormones, along with steroidogenic gene expression, declined significantly, in spite of the upregulation of genes involved in cholesterol synthesis. Out of 12,385 differentially expressed genes (DEGs), 330 significant DEGs (75 upregulated, 225 downregulated) were subjected to KEGG functional pathway annotation, gene ontology enrichment, STRING network analyses and manual querying of DEGs for meaningful molecular mechanisms. High inflammatory response was found to be responsible for oxidative-stress-mediated apoptosis of GCs and nodes towards the involvement of the NF-κB pathway and repression of the Nrf2 pathway. Downregulation of MDM4, TP53, PIDD1, PARP3, MAPK14 and MYC, and upregulation of STK26, STK33, TGFB2, CDKN1A and CDKN2A, at the interface of the MAPK and p53 signaling pathway, can be attributed to transient cellular senescence and apoptosis in GCs. The background working of the AMPK pathway through upregulation of AKT1, AMPK, SIRT1, PYGM, SLC2A4 and SERBP1 genes, and downregulation of PPARGCIA, IGF2, PPARA, SLC27A3, SLC16A3, TSC1/2, KCNJ2, KCNJ16, etc., evidence the repression of cellular transcriptional activity and energetic homeostasis modifications in response to heat stress. This study presents detailed responses of acute-heat-stressed GCs at physical, transcriptional and pathway levels and presents interesting insights into future studies regarding GC adaptation and their interaction with oocytes and the reproductive system at the ovarian level.