Genetic parameters for hair characteristics and core body temperature in a multibreed Brahman-Angus herd1

Skin transcriptome analysis in Brangus cattle under heat stress

Heat stress is a major factor that negatively affects animal welfare and production systems. Livestock should adapt to tropical and subtropical areas and to meet this, composite breeds have been developed. This work aimed to evaluate gene expression profiles in the skin of Brangus cattle under heat stress using a case-control design, and to correlate this with skin histological characteristics. Two groups of bulls were set using rectal temperature as a criterion to define stress conditions: stressed (N = 5) and non-stressed (N = 5) groups. Skin transcriptomics was performed and correlations between breed composition, phenotypic and skin histological traits were evaluated. Results showed 4309 differentially expressed genes (P < 0.01), 2113 downregulated and 2196 upregulated. Enrichment and ontology analyses revealed 132 GO terms and 67 pathways (P < 0.01), including thermogenesis, glycolysis, gluconeogenesis, mitochondrial activity, antioxidant and immune response, and apoptosis. The identity of the terms and pathways indicated the diversity of mechanisms directed to relieve the animals' suffering, acting from simple passive mechanisms (conduction, convection and radiation) to more complex active ones (behavioural changes, evaporation, vasodilation and wheezing). Furthermore, significant differences between phenotypic and skin histological traits and correlations between pairs of traits suggested a direction towards heat dissipation processes. In this sense, number of vessels was positively correlated with number of sweat glands (P < 0.001) and both were positively correlated with zebuine genetic content (P < 0.05 and P < 0.01, respectively), gland size was positively correlated with epidermal thickness and negatively with hair length (P < 0.05), and epidermal thickness was negatively correlated with gland-epidermis distance (P < 0.0005). These results support the notion that response to heat stress is physiologically complex, producing significant changes in the expression of genes involved in several biological pathways, while the animal's ability to face it depends greatly on their skin features.

Late-gestation heat stress in Holstein dams programs in utero development of daughter's germline, triggering skin and hair morphology adaptations of granddaughters

Homeostasis and thermoregulation are influenced by the interplay of hair coat and skin characteristics. Our previous work indicated that hair and skin adaptations, triggered by in utero heat stress, affect thermoregulation in postnatal life. Herein, we investigate multigenerational carry-over effects of late-gestation heat stress on hair and skin characteristics beyond the first generation. Pregnant Holstein dams (F0, grand-dams) were heat stressed (HT, shade, n = 41) or provided active cooling (CL, shade, fans, and water soakers, n = 41) for the last 56 d of gestation during summer (temperature-humidity index ≥68). The first generation of heifers (F1, daughters) who were in utero heat stressed (HTF1, n = 36) or not (CLF1, n = 37) were born and raised as a cohort from birth to first calving. Thirty second-generation heifers (F2, granddaughters), born to HTF1 (HTF2, n = 12) and CLF1 (CLF2, n = 18), were raised as a cohort from birth to 70 d of age. Hair samples and skin biopsies from HTF2 and CLF2 were collected on postnatal d 70 (n = 6/group). Hair samples were subdivided into topcoat and undercoat, and skin tissue was fixed for ~18 h in 10% formalin, dehydrated, paraffin-embedded, sectioned, and stained with hematoxylin and eosin to visualize morphology. Variables analyzed included hair length and diameter; stratum corneum cross-sectional area and thickness; epidermis thickness; sweat gland depth, number, cross-sectional area, and average size; and sebaceous gland number, cross-sectional area, and average size. Measurements were performed using the ImageJ software and analyzed using PROC MIXED in SAS (SAS Institute Inc.). Hair length and diameter tended to be shorter and thicker in HTF2, compared with CLF2. The HTF2 skin had smaller stratum corneum cross-sectional area and tended to a thinner epidermis. to CLF2, HTF2 skin had more but smaller sebaceous glands, whereas no differences in sweat glands were observed. In summary, we report phenotypic alterations in hair and skin characteristics of granddaughters. Whether these adaptations grant improved postnatal thermoregulatory ability for the granddaughters remains to be investigated.

Blood Transcriptomic Analyses Reveal Functional Pathways Associated with Thermotolerance in Pregnant Ewes Exposed to Environmental Heat Stress

Environmental heat stress triggers a series of compensatory mechanisms in sheep that are dependent on their genetic regulation of thermotolerance. Our objective was to identify genes and regulatory pathways associated with thermotolerance in ewes exposed to heat stress. We performed next-generation RNA sequencing on blood collected from 16 pregnant ewes, which were grouped as tolerant and non-tolerant to heat stress according to a physiological indicator. Additional samples were collected to measure complete blood count. A total of 358 differentially expressed genes were identified after applying selection criteria. Gene expression analysis detected 46 GO terms and 52 KEGG functional pathways. The top-three signaling pathways were p53, RIG-I-like receptor and FoxO, which suggested gene participation in biological processes such as apoptosis, cell signaling and immune response to external stressors. Network analysis revealed ATM, ISG15, IRF7, MDM4, DHX58 and TGFβR1 as over-expressed genes with high regulatory potential. A co-expression network involving the immune-related genes ISG15, IRF7 and DXH58 was detected in lymphocytes and monocytes, which was consistent with hematological findings. In conclusion, transcriptomic analysis revealed a non-viral immune mechanism involving apoptosis, which is induced by external stressors and appears to play an important role in the molecular regulation of heat stress tolerance in ewes.

Extracellular vesicle-microRNAs mediated response of bovine ovaries to seasonal environmental changes

BACKGROUND

Among the various seasonal environmental changes, elevated ambient temperature during the summer season is a main cause of stress in dairy and beef cows, leading to impaired reproductive function and fertility. Follicular fluid extracellular vesicles (FF-EVs) play an important role in intrafollicular cellular communication by, in part, mediating the deleterious effects of heat stress (HS). Here we aimed to investigate the changes in FF-EV miRNA cargoes in beef cows in response to seasonal changes: summer (SUM) compared to the winter (WIN) season using high throughput sequencing of FF-EV-coupled miRNAs. In addition to their biological relevance, the potential mechanisms involved in the packaging and release of those miRNAs as a response to environmental HS were elucidated.

RESULTS

Sequencing analysis revealed that an average of 6.6% of the EV-RNA mapped reads were annotated to bovine miRNAs. Interestingly, miR-148a, miR-99a-5p, miR-10b, and miR-143 were the top four miRNAs in both groups accounting for approximately 52 and 62% of the total miRNA sequence reads in the SUM and WIN groups, respectively. A group of 16 miRNAs was up-regulated and 8 miRNAs were down-regulated in the SUM compared to the WIN group. Five DE-miRNAs (miR-10a, miR-10b, miR-26a, let-7f, and miR-1246) were among the top 20 expressed miRNA lists. Sequence motif analysis revealed the appearance of two specific motifs in 13 out of the 16 upregulated miRNAs under HS conditions. Both motifs were found to be potentially bonded by specific RNA binding proteins including Y-box binding proteins (YBX1 and YBX2) and RBM42.

CONCLUSION

Our findings indicate that FF EV-coupled miRNA profile varies under seasonal changes. These miRNAs could be a good indicator of the cellular mechanism in mediating HS response and the potential interplay between miRNA motifs and RNA binding proteins can be one of the mechanisms governing the packaging and release of miRNAs via EVs to facilitate cellular survival.

Phenotypic and genetic parameters of circadian rhythms from core body temperature profiles and their relationships with beef steers' production efficiency profiles during successive winter feeding periods

This 2-year study evaluated differences in circadian parameters obtained from measures of core body temperatures using telemetric reticulo-rumen and rectal devices during two winter feeding regimes in western Canada. The study also estimated phenotypic correlations and genetic parameters associated with circadian parameters and other production traits in each feeding regime. Each year, 80 weaned steer calves (initial age: 209 ± 11 days; BW: 264 ± 20 kg) from the same cohort were tested over two successive regimes, Fall-Winter (FW) and Winter-Spring (WS) at Lanigan, Saskatchewan, Canada. The steers received forage-based rations in both regimes where the individual feed intake was measured with automatic feeding units. During the trial, the reticulo-rumen (RTMP) and rectal (RCT) temperatures were simultaneously measured every 5 min using telemetric devices. These were used to calculate the circadian parameters (Midline Estimating Statistic Of Rhythms, amplitude, and acrophase/peak time) for both temperature measures. Growth and efficiency performance traits were also determined for all steers. Each steer was assigned into inefficient, neutral, and efficient classes based on the SD of the residual feed intake (RFI), residual gain (RG), and residual intake and gain (RIG) within each year and feeding regime. Higher (p < 0.0003) RTMP and rectal temperature MESORs were observed in the Fall-Winter compared to the Winter-Spring regime. While the two test regimes were different (p < 0.05) for the majority of the RTMP or RCT temperature parameters, they did not differ (p > 0.10) with the production efficiency profiles. The heritability estimates were higher in FW (0.78 ± 0.18 vs. 0.56 ± 0.26) than WS (0.50 ± 0.18 vs. 0.47 ± 0.22) for the rumen and rectal MESORs, respectively. There were positive genetic correlations between the two regimes for the RTMP (0.69 ± 0.21) and RCT (0.32 ± 0.59). There was a negative correlation (p < 0.001) between body temperature and ambient temperature. The high heritability estimates and genetic correlations for rumen and rectal temperature parameters demonstrate their potential as beef genetic improvement tools of economic traits associated with the parameters. However, there are limited practical implications of using only the core-body temperature as a proxy for production efficiency traits for beef steers during winter.

Removing maternal heat stress abatement during gestation modulated postnatal physiology and improved performance of Bos indicus-influenced beef offspring

This study evaluated the growth and immune response of beef calves born from Bos indicus-influenced beef heifers provided pre- and postpartum heat abatement on pasture. On 83 ± 4 d prepartum (day 0), 64 Brangus crossbred beef heifers (~¼ B. indicus) were stratified by body weight (BW; 454 ± 37 kg) and body condition score (BCS; 6.3 ± 0.28; scale 1 to 9), and then allocated into 1 of 16 bahiagrass pastures (1 ha and 4 heifers per pasture). Treatments were randomly assigned to pastures (8 pastures per treatment) and consisted of heifers provided (SH) or not (NSH) access to artificial shade (4.5 m2 of shade area per heifer) from 83 d prepartum to 50 d postpartum (days 0 to 133). Heifers and calves were managed similarly from day 133 until the start of the breeding season (day 203). Calves were weaned on day 203 (at 119 ± 19 d of age), limit-fed the same drylot diet at 3.5% of BW (DM basis) days 209 to 268 (3 to 4 calves per pen; 8 pens per treatment) and vaccinated against respiratory disease pathogens on days 222 and 236. Heifer intravaginal temperatures from days 35 to 42 were lower (P ≤ 0.03) for NSH vs. SH heifers from 0000 to 0800 hours but greater (P ≤ 0.05) for NSH vs. SH heifers from 1100 to 1800 hours. Heifer intravaginal temperature from days 126 to 132 did not differ (P = 0.99) between NSH and SH heifers. Heifers assigned to NSH had greater respiration rates from days 20 to 96 (P ≤ 0.0007), greater plasma concentration of cortisol on days 35 (P = 0.07) and 55 (P = 0.02), less plasma concentration of insulin-like growth factor 1 (IGF-1) on days 35 (P = 0.10), 55, and 133 (P ≤ 0.05), and less BCS from days 55 to 203 (P ≤ 0.01) compared to SH heifers. Calves born from NSH heifers had less birth BW (P = 0.05), greater overall plasma haptoglobin concentrations (P = 0.05), greater seroconversion against bovine respiratory syncytial virus on day 222 (P = 0.02), tended to have greater ADG from days 209 to 268 (P = 0.07), and had greater BW on day 268 (P = 0.05) compared to SH offspring. Plasma concentrations of cortisol and serum titers against other respiratory disease pathogens did not differ (P ≥ 0.15) between NSH and SH offspring. Hence, removing maternal access to artificial shade: (1) increased prepartum intravaginal temperature and plasma concentrations of cortisol but reduced prepartum BCS and plasma concentrations of IGF-1 in grazing B. indicus-influenced beef heifers; and (2) increased post-weaning BW gain and had positive effects on humoral immune response of their offspring.

Effect of in utero exposure to hyperthermia on postnatal hair length, skin morphology, and thermoregulatory responses

Skin and hair coat play important functions in maintaining homeostasis and thermoregulation for cattle, which can affect all modes of heat loss. Our objective was to investigate the effect of hyperthermia experienced in utero during late gestation on postnatal hair length, skin properties, and thermoregulation. Pregnant dams were heat stressed (n = 41) or actively cooled (n = 41) for the last ∼56 d of gestation and gave birth to heifers that were in utero heat stressed (IUHT) or in utero cooled (IUCL), respectively. Hair samples and skin tissue biopsies were collected from neck and rump locations at birth (d 0), 1 wk after weaning (d 63), and at 12 mo. Hair samples were also obtained at 4 and 8 mo. Skin tissue was stained with hematoxylin and eosin to visualize morphology. Hair length (short and long hairs, undercoat and topcoat, respectively), stratum corneum (SC) area, SC thickness, epidermis thickness, sweat gland (SWT) number, SWT cross-sectional area, SWT average size, sebaceous gland (SEB) number, SEB cross-sectional area, SEB average size, and sweat gland depth were assessed. Respiration rate, skin temperature, sweating rate, and rectal temperature was measured weekly from d 7 to 63. Additionally, thermoregulatory patterns were measured every 4 h over a 36-h interval beginning 4 d after weaning. Data were analyzed using PROC MIXED in SAS with a main effect of in utero treatment with location and time points analyzed separately. No difference in hair parameters were detected at d 0 or 12 mo. At d 63, IUHT heifers had longer average hair length (14.8 vs. 13.8 ± 0.2 mm, standard error), shorter undercoats (9.3 vs. 10.4 ± 0.3 mm), longer topcoats (19.6 vs. 17.1 ± 0.3 mm), and a greater difference between topcoat and undercoat (10.1 vs. 7.0 ± 0.4 mm). At 4 mo, IUHT heifers had longer average hair lengths (26.1 vs. 22.2 ± 1.0 mm) and longer topcoats (36.9 vs. 33.9 ± 1.1 mm), and at 8 mo, IUHT had longer average hair lengths (17.9 vs. 16.2 ± 0.6 mm), relative to IUCL. At d 0, IUHT heifers had more (13 vs. 9 ± 2 glands) but smaller average sized SEB (neck: 1,636 vs. 2,238 ± 243 µm²; rump: 2,100 vs. 3,352 ± 379 µm²) and reduced SC area (79,243 vs. 169,419 ± 13,071 µm²). At d 63, IUHT had fewer SEB (11 vs. 15 ± 2 glands), smaller SWT (0.16 vs. 0.23 ± 0.02 mm²), fewer SWT (16 vs. 23 ± 4 glands), and deeper SWT (0.5 vs. 0.4 ± 0.03 mm). At 12 mo, IUHT had greater distance from the skin surface to the most superficial SWT (0.016 vs. 0.015 ± 0.0004 mm), shorter distance to the deepest SWT (0.031 vs. 0.033 ± 0.001 mm), and smaller SWT (81.1 vs. 108.9 ± 10.8 µm²), relative to IUCL. When measured both weekly and hourly, IUHT heifers had higher rectal temperature and sweating rate. Overall, in utero hyperthermia triggers long-lasting hair and skin adaptations, possibly leading to differences in postnatal thermoregulation.

Stair step strategy and immunomodulatory feed ingredient supplementation for grazing heat-stressed Bos indicus-influenced beef heifers

On day 0 of year 1 and 2, sixty-four Brangus crossbred heifers per year were stratified by initial body weight (BW) and age (mean = 257 ± 20 kg and 271 ± 22 d) and allocated into 16 bahiagrass (Paspalum notatum) pastures (4 heifers/pasture/yr). Treatments were randomly allotted to pastures in a 2 × 2 factorial arrangement of treatments (4 pastures/treatment/yr). Treatments consisted of concentrate dry matter (DM) supplementation at 1.50% of BW from day 0 to 100 (CON) or concentrate DM supplementation at 1.05% of BW from day 0 to 49 and 1.95% of BW from day 50 to 100 (SST). Then, each respective supplementation strategy was added or not with immunomodulatory feed ingredient from day 0 to 100 (OMN; 4 g/45 kg of BW). Heifers were assigned to an estrus synchronization protocol from day 100 to 114. Heifers detected in estrus from day 111 to 114 were inseminated (AI) 12 h after estrus detection. Heifers not detected in estrus were timed AI on day 114. All heifers were exposed to Angus bulls from day 120 to 210 (1 bull/pasture). Effects of supplementation strategy × OMN inclusion × hour were detected (P < 0.0001) only for intravaginal temperature from day 26 to 30, which were the least (P ≤ 0.03) for SST heifers offered OMN supplementation and did not differ (P ≥ 0.17) among all remaining treatments from 0830 to 1600 h. Effects of supplementation strategy × OMN inclusion and OMN inclusion were not detected (P ≥ 0.12) for any variable, except for percentage of heifers detected in estrus, which was greater (P = 0.01) for heifers supplemented with vs. without OMN. Total concentrate DM offered from day 0 to 100 and heifer BW on days 0 and 56 did not differ (P ≥ 0.49) between CON and SST heifers, but SST heifers were heavier (P ≤ 0.01) on days 100 and 210 compared to CON heifers. Body surface temperature on day 25 and plasma IGF-1 concentrations on day 75 were greater (P ≤ 0.04) for SST vs. CON heifers. Percentage of pubertal heifers, heifers detected in estrus, and pregnancy to AI did not differ (P = 0.36) between SST and CON heifers but final pregnancy percentage was greater (P = 0.04) for SST vs. CON heifers. Thus, OMN supplementation decreased intravaginal temperature of SST heifers but failed to improve their growth and reproduction, whereas the SST strategy improved body thermoregulation, growth, and final pregnancy percentage of heat stressed Bos indicus-influenced beef heifers compared to a constant concentrate supplementation strategy.

Coat score. A possible explanation for the zebuine selective sweep located on bovine chromosome 5: 47,670,001-48,100,000 bp

Over 65% of the world's cattle population resides in warm areas where heat stress conditions limit the breed of European taurine cattle. Composite breeds were developed to retain the main traits of both parental breeds. The skin plays a central role in animal response to heat stress. Research on the genetic architecture of skin traits has identified genes and regions related to warm resistance skin features. The aim of this study was to determine whether the indicine proportion accounted for coat type or whether there were genes of large effect segregating in Brangus. Bulls (n = 108) were genotyped using microarrays and their coat score and hair length were evaluated. Indicine-taurine genome-wide composition was estimated and GWAS was performed. Although significant correlations between indicine proportion and traits were not observed, four windows of SNPs on BTA4 and BTA5 explained more than 2% of the trait variance. The GWAS for coat score in summer showed the main peak on BTA5:46,941,446-48,030,219 bp, accounting for 4.65% of the variance. Our results suggest that the variation in coat score and undercoat hair length in Argentinian Brangus bulls is associated with the presence of some particular gene variants, rather than with the whole indicine genetic content.

Connecting Heat Tolerance and Tenderness in Bos indicus Influenced Cattle

Simple Summary

Bos indicus (also known as zebu or humped) cattle are heat tolerant and parasite resistant, which is advantageous in hot, humid climates. However, Bos indicus cattle are also known for excitable temperaments, slower growth, and variation in meat quality characteristics. The relationships between thermotolerance, temperament, and meat production traits are poorly understood. Due to its contribution to body weight, muscle may play an important role in determining the thermoregulatory capacity of Bos indicus cattle. Ultimately, defining relationships between muscle metabolism and heat tolerance are necessary in order to enhance tenderness, without sacrificing heat tolerance of Bos indicus breeds.

Abstract

Bos indicus cattle are widely utilized in tropical and subtropical climates. Their heat tolerance and parasite resistance are integral for beef production in these regions; however, a reputation for excitable temperaments, slower growth, and variation in tenderness has limited their use in commercial beef production. This suggests that there is antagonism between heat tolerance and meat production traits. Meat quality characteristics are determined by the properties of skeletal muscle as well as conditions during slaughter and processing. Thus, it is possible that adaptations related to heat tolerance in the living animal affect tenderness and other meat quality attributes. Since muscle represents a large proportion of body mass, relatively small changes at the cellular level could impact overall heat production of the animal. Specifically, protein degradation and mitochondria function are aspects of organ and cellular metabolism that may help limit heat production and also have a connection to tenderness. Protein degradation postmortem is critical to structural changes that enhance tenderness whereas mitochondria may influence tenderness through their roles in energy metabolism, calcium regulation, cell death signaling, and oxidative stress. This review explores potential relationships between cellular metabolism in vivo and beef quality development in Bos indicus and Bos indicus influenced cattle.

The Genetics of Thermoregulation in Pigs: A Review

Heat stress (HS) affects pig performance, health and welfare, resulting in a financial burden to the pig industry. Pigs have a limited number of functional sweat glands and their thermoregulatory mechanisms used to maintain body temperature, are challenged by HS to maintain body temperature. The genetic selection of genotypes tolerant to HS is a promising long-term (adaptation) option that could be combined with other measures at the production system level. This review summarizes the current knowledge on the genetics of thermoregulation in pigs. It also discusses the different phenotypes that can be used in genetic studies, as well as the variability in thermoregulation between pig breeds and the inheritance of traits related to thermoregulation. This review also considers on-going challenges to face for improving heat tolerance in pigs.

Daily vaginal temperature in Girolando cows from three different genetic composition under natural heat stress

The present trial evaluated the effect of crossbred composition and Temperature and Humidity Index (THI) on vaginal temperature (VT) of Girolando dairy cows maintained under tropical pasture during warm seasons. The VT was monitored along 41 to 96 h in 615 Girolando cows with different Holstein (H) × Gir genetic composition (1/2 H = 284, 3/4 H = 248, and 7/8 H = 83) from six Brazilian farms in the summer of 2016 and 2017. VT of each cow at each hour of the day and the respective THI were averaged per hour across all monitoring days to generate an averaged value for VT and THI during 24 h. A linear mixed model with repeated measures using restricted maximum likelihood (REML) method for (co)variance components estimation procedure was employed. The final model adjusted the VT for the effects of cow, time, THI, farm, year, pregnancy status, body condition score (BCS), milk yield, genetic composition, and genetic composition*time interaction. Fixed effects were evaluated by ANOVA and tested with Tukey test in R software version 3.6.1 (R Core Team, 2019). Overall mean of VT, air temperature (AT), and THI were 39.06 ± 0.52 °C, 25.63 ± 0.40 °C, and 75.06 ± 3.96, respectively. VT had moderate positive correlation with THI (r² = 0.45, P < 0.001) and AT (r² = 0.46, P < 0.001). The VT had estimated linear increase of 0.05 °C for each THI unit increase (P < 0.001). Least square mean of VT varied among the farms (P < 0.001), pregnancy status (P < 0.001), and BCS (P < 0.05) but not for Milk yield (P > 0.05). The daily average VT was affected by genetic composition (P < 0.001) with highest temperature for 3/4 H (39.08 ± 0.06 °C a) and 7/8 H (39.09 ± 0.06 °C a) and lowest temperature for 1/2 H (38.95 ± 0.06 °C b). The difference of VT among the three crossbred groups varied in function of the time of the day, from 12:00 to 20:00 h (P < 0.001), with 3/4 Holstein and 7/8 Holstein cows reaching similar VT, above to the upper limit 39.1 °C and higher than 1/2 Holstein cows during all this period. In conclusion, Girolando cows are sensitive to heat stress in tropical condition during warm seasons. Moreover, Girolando cows with genetic composition higher than 3/4 Holstein display reduced thermoregulatory efficiency. Therefore, Girolando cows in tropical dairy farms require strategies to mitigate heat stress according to their genetic composition.

Genomic analyses and biological validation of candidate genes for rectal temperature as an indicator of heat stress in Holstein cattle

Heat stress is a major cause of welfare issues and economic losses to the worldwide dairy cattle industry. Genetic selection for heat tolerance has a great potential to positively affect the dairy industry, as the gains are permanent and cumulative over generations. Rectal temperature (RT) is hypothesized to be a good indicator trait of heat tolerance. Therefore, this study investigated the genetic architecture of RT by estimating genetic parameters, performing genome-wide association studies, and biologically validating potential candidate genes identified to be related to RT in Holstein cattle. A total of 33,013 RT records from 7,598 cows were used in this study. In addition, 1,114 cows were genotyped using the Illumina 150K Bovine BeadChip (Illumina, San Diego, CA). Rectal temperature measurements taken in the morning (AMRT) and in the afternoon (PMRT) are moderately heritable traits, with estimates of 0.09 ± 0.02 and 0.04 ± 0.01, respectively. These 2 traits are also highly genetically correlated (r = 0.90 ± 0.08). A total of 10 SNPs (located on BTA3, BTA4, BTA8, BTA13, BTA14, and BTA29) were found to be significantly associated with AMRT and PMRT. Subsequently, gene expression analyses were performed to validate the key functional genes identified (SPAG17, FAM107B, TSNARE1, RALYL, and PHRF1). This was done through in vitro exposure of peripheral blood mononuclear cells (PBMC) to different temperatures (37°C, 39°C, and 42°C). The relative mRNA expression of 2 genes, FAM107B and PHRF1, significantly changed between the control and heat stressed PBMC. In summary, RT is heritable, and enough genetic variability exists to enable genetic improvement of heat tolerance in Holstein cattle. Important genomic regions were identified and biologically validated; FAM107B and PHRF1 are the main candidate genes identified to influence heat stress response in dairy cattle.

Genome-wide association study identifies variants associated with hair length in Brangus cattle

Thermal stress limits beef cattle production and a shorter hair coat is a key thermoregulative adaptation that allows cattle to lose heat more efficiently. The objective of this study was to identify genetic variants associated with the length of the undercoat and topcoat of cattle utilizing 1456 Brangus heifers genotyped with the Bovine GGP F250 array. Seven SNPs in the PCCA gene were significantly associated with undercoat length. PCCA belongs to the biotin transport and metabolism pathway. Biotin deficiency has been reported to cause hair loss. Four SNPs in an 110 kb including a missense mutation in the PRLR gene were significantly associated with topcoat length. Whereas the association of this polymorphism with hair length is novel, the SLICK mutation in PRLR has previously been demonstrated to significantly impact hair length in cattle. These newly detected genetic variants may contribute to a shorter hair coat and more thermotolerant animals.

Prospects for gene introgression or gene editing as a strategy for reduction of the impact of heat stress on production and reproduction in cattle

In cattle, genetic variation exists in regulation of body temperature and stabilization of cellular function during heat stress. There are opportunities to reduce the impact of heat stress on cattle production by identifying the causative mutations responsible for genetic variation in thermotolerance and transferring specific alleles that confer thermotolerance to breeds not adapted to hot climates. An example of a mutation conferring superior ability to regulate body temperature is the group of frame-sift mutations in the prolactin receptor gene (PRLR) that lead to a truncated receptor and development of cattle with a short, sleek hair coat. Slick mutations in PRLR have been found in several extant breeds derived from criollo cattle. The slick mutation in Senepol cattle has been introgressed into dairy cattle in Puerto Rico, Florida and New Zealand. An example of a mutation that confers cellular protection against elevated body temperature is a deletion mutation in the promoter region of a heat shock protein 70 gene called HSPA1L. Inheritance of the mutation results in amplification of the transcriptional response of HSPA1L to heat shock and increased cell survival. The case of PRLR provides a promising example of the efficacy of the genetic approach outlined in this paper. Identification of other mutations conferring thermotolerance at the whole-animal or cellular level will lead to additional opportunities for using genetic solutions to reduce the impact of heat stress.

Mitochondrial oxygen consumption in early postmortem permeabilized skeletal muscle fibers is influenced by cattle breed

Functional properties and integrity of skeletal muscle mitochondria (mt) during the early postmortem period may influence energy metabolism and pH decline, thereby impacting meat quality development. Angus typically produce more tender beef than Brahman, a Bos indicus breed known for heat tolerance. Thus, our objectives were to compare mt respiratory function in muscle collected early postmortem (1 h) from Angus and Brahman steers (n = 26); and to evaluate the effect of normal and elevated temperature on mt function ex vivo. We measured mt oxygen consumption rate (OCR) in fresh-permeabilized muscle fibers from Longissimus lumborum (LL) at 2 temperatures (38.5 and 40.0 °C) and determined citrate synthase (CS) activity and expression of several mt proteins. The main effects of breed, temperature, and their interaction were tested for mt respiration, and breed effect was tested for CS activity and protein expression. Breed, but not temperature (P > 0.40), influenced mt OCR (per tissue weight), with Brahman exhibiting greater complex I+II-mediated oxidative phosphorylation capacity (P = 0.05). Complex I- and complex II-mediated OCR also tended to be greater in Brahman (P = 0.07 and P = 0.09, respectively). Activity of CS was higher in LL from Brahman compared to Angus (P = 0.05). Expression of specific mt proteins did not differ between breeds, except for higher expression of adenosine triphosphate (ATP) synthase subunit 5 alpha in Brahman muscle (P = 0.04). Coupling control ratio differed between breeds (P = 0.05), revealing greater coupling between oxygen consumption and phosphorylation in Brahman. Our data demonstrate that both Angus and Brahman mt retained functional capacity and integrity 1-h postmortem; greater oxidative phosphorylation capacity and coupling in Brahman mt could be related to heat tolerance and impact early postmortem metabolism.

A comparison of milk production from Holstein Friesian and Jersey cattle breeds under hot climate of Oman

Data of milk production and performance under Oman climatic conditions are limited. The current study presents a 9-year analysis of daily milk performance of Holstein and Jersey cattle breeds born and raised in Oman and fed similar diets of concentrate and Rhodes grass hay. Data on the daily cow's milk production, during the entire lactation period for nine consecutive milking years between 2009 and 2018, were collected. The data was introduced to a linear mixed model and was analyzed to evaluate the breed variations in milk production across lactations and across years. Holstein Friesian (HF) cows had significantly (P < 0.001) higher daily milk production of 17.6 ± 0.4 kg/cow/day compared to 11.7 ± 0.8 kg/cow/day for Jersey cows. Across years, we observed a gradual annual improvement in total milk production in both HF and Jersey breeds of 5% and 6%, respectively. The highest daily milk production was in the third and fourth lactations for HF cows and in the second and third lactations for Jersey cows. In a region where much of the expected demand in milk will be met by exotic breeds and importation, our results provide an insight into the performance of temperate breeds in hot and arid climatic conditions. As such, our results shall be useful for dairy producers seeking to maximize milk production under such conditions.