Heat Tolerance In Cattle Research Articles

Impact of Brahman genetics on skin histology characteristics with implications for heat tolerance in cattle.

Cattle lose heat predominantly through cutaneous evaporation at the skin-hair coat interface when experiencing heat stress. Sweating ability, sweat gland properties, and hair coat properties are a few of the many variables determining the efficacy of evaporative cooling. Sweating is a significant heat dissipation mechanism responsible for 85% of body heat loss when temperatures rise above 86⁰F. The purpose of this study was to characterize skin morphological parameters in Angus, Brahman, and their crossbred cattle. Skin samples were taken during the summer of 2017 and 2018 from a total of 319 heifers from six breed groups ranging from 100% Angus to 100% Brahman. Epidermis thickness decreased as the percentage of Brahman genetics increased where the 100% Angus group had a significantly thicker epidermis compared to the 100% Brahman animals. A more extended epidermis layer was identified in Brahman animals due to more pronounced undulations in this skin layer. Breed groups with 75% and 100% Brahman genes were similar and had the largest sweat gland area, indicative of superior resilience to heat stress, compared to breed groups with 50% or lower Brahman genetics. There was a significant linear breed group effect on sweat gland area indicating an increase of 862.0µm2 for every 25% increase in Brahman genetics. Sweat gland length increased as the Brahman percentage increased, while the sweat gland depth showed an opposite trend, decreasing from 100% Angus to 100% Brahman. The number of sebaceous glands was highest in 100% Brahman animals which had about 1.77 more sebaceous glands (p < 0.05) per 4.6 mm2area. Conversely, the sebaceous gland area was greatest in the 100% Angus group. This study identified significant differences in skin properties related to heat exchange ability between Brahman and Angus cattle. Equally important, these differences are also accompanied by significant levels of variation within each breed, which is indicative that selection for these skin traits would improve the heat exchange ability in beef cattle. Further, selecting beef cattle for these skin traits would lead to increased resilience to heat stress without disrupting production traits.

Climate Change and Globalization: Food Security in the Caribbean

Climate change and food security are among the world’s biggest challenges. A growing population and climate change means that vulnerable regions such as the Caribbean, will continue to face unique strains. The effects of climate change are associated with poverty and a decrease in food security because of the decline in food production and access to a sufficient amount of nutritious food. Trade liberalization increases the number of challenges experienced by notably, the local Caribbean agricultural sector and has devastating effects on food security and rural livelihoods. Reductions in crop diversity and production mixed with low household incomes results in changed diets. These changes have increased the prevalence of non-communicable diseases (NCDs) such as diabetes and hypertension as well as obesity and other long-term health problems. Current and proposed strategies to aid with the challenges of climate change include further research on the creation of heat tolerant cattle breeds, technological developments, micro-insurance interventions, and the expansion of greenhouse farming. The traditional and acquired knowledge and skills of individuals in the agricultural sector is fundamental in creating strategies to adapt to the impacts of climate change and it is essential to ensure the strengthening of food security and food sovereignty. Financial resources in the Caribbean are inadequate and therefore, it is imperative that the Global North pay their dues in shouldering the responsibility of reducing the economic and environmental vulnerabilities in the Caribbean.

Revealing the diversity of internal body temperature and panting response for feedlot cattle under environmental thermal stress

Core body temperature (CBT) regulation is crucial for mammalian wellbeing and survival. Cattle pant to dissipate excess heat to regulate CBT when ambient conditions exceed thermoneutral zones. However, to date, neither the variability in cattle heat response, the lagged response of CBT to thermal indices, nor the diurnal patterns of thermal indices, CBT and panting have been reported in the literature. We decomposed thermal indices, CBT and panting time-series data for 99 feedlot heifers across three discrete heat events into diurnal, trend and residual components. Both raw and decomposed data were analysed to explore the lagged CBT and panting responses and the association between series. We show ambient thermal conditions impact CBT with a 1-h lag despite a lag of between 1.5 to 3 h from raw data. Average individual panting scores were used to identify heat-susceptible and heat-tolerant cattle. Heat-susceptible cattle showed greater CBT (P < 0.01) between 8:00 and 23:00 and greater panting duration (P < 0.05) between 10:00 and 18:00 than heat-tolerant cattle under the same thermal conditions and these variations followed a similar pattern despite differences in cattle breed. This new information enables targeted amelioration and selection of individuals against heat susceptibility.

Genetic polymorphism in HSPB6 gene and their association with heat tolerance in Sahiwal cattle

Heat shock proteins (HSPs) are known to modulate cellular response during summer stress in dairy cattle. Among different classes of HSPs, heat shock protein 20 (HSPB6) is a member of the small HSP family protein, the role of which has not been fully characterized in the context of heat stress in cattle. This study identified single nucleotide polymorphisms (SNPs) in the HSPB6 gene in Sahiwal cattle and their associations with heat tolerance traits (RR, RT and HTC). Three SNPs (SNP 1-3) were reported, which included two transitions, viz. SNP1-g.436G&gt;A (Intron 1) and SNP2-g.2152A&gt;G (3′-UTR) and one transversion, viz. SNP3-g.2417A&gt;T (3′-UTR). The association analysis revealed that SNPs loci, viz. SNP1-g.436G&gt;A and SNP2-g.2152A&gt;G were significantly associated with heat tolerance traits. The GG genotype of SNP2-g.2152A&gt;G was significantly associated with heat tolerance traits in Sahiwal cattle. The association analysis of four available haplotypes, viz. Hap1 (GGA), Hap2 (AAA), Hap3 (GAA), and Hap4 (AAT) of HSPB6 gene with heat tolerance traits did not differ significantly with any haplotype in Sahiwal cattle. This study provides the first association analyses between the SNPs of HSPB6 gene and heat tolerance traits in Sahiwal cattle, which could be used as effective SNP markers in genetic selection for heat tolerance in cattle breeding programs.

The Association between Gut Microbiome Diversity and Composition and Heat Tolerance in Cattle.

Cattle are raised around the world and are frequently exposed to heat stress, whether in tropical countries or in regions with temperate climates. It is universally acknowledged that compared to those in temperate areas, the cattle breeds developed in tropical and subtropical areas have better heat tolerance. However, the underlying mechanism of heat tolerance has not been fully studied, especially from the perspective of intestinal microbiomics. The present study collected fecal samples of cattle from four representative climatic regions of China, namely, the mesotemperate (HLJ), warm temperate (SD), subtropical (HK), and tropical (SS) regions. Then, the feces were analyzed using high-throughput 16S rRNA sequencing. The results showed that with increasing climatic temperature from HLJ to SS, the abundance of Firmicutes increased, accompanied by an increasing Firmicutes to Bacteroidota ratio. Proteobacteria showed a trend of reduction from HLJ to SS. Patescibacteria, Chloroflexi, and Actinobacteriota were particularly highest in SS for adapting to the tropical environment. The microbial phenotype in the tropics was characterized by an increase in Gram-positive bacteria and a decrease in Gram-negative bacteria, aerobic bacteria, and the forming of_biofilms. Consistently, the functional abundances of organismal systems and metabolism were decreased to reduce the material and energy demands in a hot environment. Genetic information processing and information storage and processing may be how gut flora deals with hot conditions. The present study revealed the differences in the structure and function of gut microbes of cattle from mesotemperate to tropical climates and provided an important reference for future research on the mechanism of heat tolerance regulated by the gut microbiota and a potential microbiota-based target to alleviate heat stress.

Using animal history to inform current debates in gene editing farm animals: A systematic review

There is growing interest in gene editing farm animals. Some alterations could benefit animal welfare (e.g., improved heat tolerance in cattle with the “slick” gene), the environment (e.g., reducing methane emissions from cattle with induced pluripotent stem cells), and productivity (e.g., higher weight gains in cattle with the “double muscling” gene). Existing scholarship on the acceptability of such modifications has used myriad approaches to identify societal factors that shape the ethics and governance of this technology. We argue that integrating historical approaches—particularly from the relatively new and burgeoning field of animal history—offers a form of “anticipatory knowledge” that can help guide discussions on this topic. We conducted a systematic review of the animal history literature in English, German, and Spanish to identify the influence of political, scientific, economic, social, and cultural factors on the development and acceptance of such technologies. We identified analogous structures and fault lines in past debates about farm animals that provide insights for contemporary discussions about gene editing. Those analogous structures include the market power of meatpackers or the racialized precepts in livestock breeding, and fault lines, like the disconnect between states and citizens over the direction of food systems. Highlighting these similarities demonstrates how external forces have shaped—and will continue to shape—the acceptance or rejection of emerging biotechnologies as applied to farm animals.

Distribution of a missense mutation (rs525805167) within the SLC45A2 gene associated with climatic conditions in Chinese cattle

SLC45A2 is involved in the synthesis of melanin transporters. We investigated the association between single nucleotide polymorphisms (SNPs) of the SLC45A2 gene and humidity and hot conditions in indigenous cattle habitat. According to the Bovine Genome Variation Database and Selective Signatures (BGVD), we explored the frequency distribution of a missense mutation (NC_037347.1: c.1543A > G, p.ser515gly) in the SLC45A2 gene in Chinese indigenous cattle. This variation from serine to glycine caused a significant change in the protein modeling structure. PCR and partial DNA sequencing were used to genotype 541 individuals, including 28 Chinese indigenous cattle breeds as well as Angus and zebu. From our results, the mutant allele frequency of this SNP in Chinese native cattle increases gradually from north to south, which is consistent with the distribution of climatic conditions in China. In addition, according to association analysis of a missense mutation (NC_037347.1: c.1543A > G) (rs525805167) in Chinese cattle, it is closely related to the annual average temperature (T), relative humidity (RH), temperature and humidity index (THI) and solar radiation time (P < 0.01). Based on the statistical analysis of the data, we assumed that rs525805167 was associated with heat tolerance traits.Simple Summary: The characteristics of Chinese indigenous cattle are closely related to their climatic environment. In China, Bos taurus is mainly distributed in the northern regions; Bos indicus is mainly distributed in southern China. In addition, the average temperature is higher in the south than in the north, and there are many mixed ancestry breeds of B. taurus and B. indicus in the middle area. The SLC45A2 gene is related to melanin synthesis, which may be closely related to heat tolerance in cattle. The purpose of our study was to investigate whether the SLC45A2 gene is related to heat tolerance in Chinese indigenous cattle.

Association of SSCP Polymorphisms of HSP70 Gene with Physiological, Production and Reproduction Performance in Sahiwal and Crossbred Cows

Background: Cellular tolerance to heat stress is mediated by heat shock proteins (HSPs). The HSPs act as molecular chaperones and are transcribed in response to stress. Among different families of these proteins, HSP70 is considered to be related to the development of temperature tolerance. Unraveling polymorphism in heat shock protein genes could be a step towards the identification of genetic markers for selecting heat-tolerant cattle. Methods: The present study was carried out in Sahiwal (n=50) and Crossbred cows (n=50) with the objective to identify polymorphisms in HSP70 gene. Two fragments (295 and 220 bp) of HSP70 gene were subjected to Polymerase Chain Reaction-Single-Strand Conformation Polymorphism (PCR-SSCP) technique. Statistical analysis was performed to study the association of each SSCP genotype on physiological, production and reproduction traits in Sahiwal and crossbred cows using the univariate GLM model of SPSS 25. Result: The PCR-SSCP of 295 bp fragment of HSP70 gene revealed two genotypes AA and AB in Sahiwal cows and two genotypes AA and AC in crossbred cows. The association analysis revealed that genotype AA had higher peak milk yield in Sahiwal cows while the same genotype had higher total lactation milk yield, lower service period and calving interval in crossbred cows. The 220 bp fragment was found to be monomorphic in both Sahiwal and crossbred cows.

Revealing the diversity in cattle behavioural response to high environmental heat using accelerometer-based ear tag sensors

Cattle heat stress responses elicit behavioural adaptation in the form of elevated respiration rate and panting with phase shifts (with increasing severity from closed mouth panting to closed mouth with drool, open mouth, and to open mouth with tongue out) and from “rapid-shallow” to “slow-deep” breathing with increasing temperature. Accelerometer-based sensors can accurately monitor cattle behaviour under experimental and commercial conditions, however, the accuracy of such sensors to monitor the different phases of panting is yet to be determined. Also, despite panting duration diversity between individual cattle of the same breed in the same environment, little is known as to why this occurs. Here we assess the ability of ear tag accelerometer sensors to monitor cattle panting severity and the diversity in behavioural response between heat-susceptible and heat-tolerant cattle when exposed to high heat load. A pen of 99 feedlot heifers were fitted with ear tag sensors and individual cattle panting responses were visually monitored for three consecutive heat event periods. Minute-level panting and non-panting individual cattle data as recorded by sensors were tested against visual observations. Sensitivity (Se), Specificity (Sp), and Youden index (J = Se + Sp – 1) were calculated as test diagnostics for sensor-based classification of panting considering the visual observations as gold standard. Raw minute-level sensor data classified all panting phases with Se 0.30–0.33, Sp > 0.70, and J > 0. Data filtering methods were applied which resulted in systematic improvements in the test diagnostics. Cattle growth, visual panting score (PS) and sensor-detected behaviour duration data were obtained for two selected heat event periods from the same animals. Variability of sensor-detected behaviour durations for visually detected heat-susceptible (PS ≥ 1) and heat-tolerant (PS < 1) category cattle were evaluated by fitting linear mixed models. The heat-susceptible cattle category had greater panting and eating and reduced resting time per day which was most pronounced in the hotter periods of the day. Susceptibility to heat could be attributed to greater growth potential and increasing eating during hotter periods and the associated metabolic heat created. In light of this key finding, adjusting feeding time may reduce the susceptibility of cattle to heat by reducing the heat increment of feeding while environmental heat is at its peak. Overall, the duration of panting and other behaviours across 24 h could be commercially practical for autonomous monitoring of panting severity in cattle, and, from a research perspective, data filtering can improve minute-level accuracy.

PSI-35 Foot and hair shedding scores of crossbred cattle grazing native rangeland differ by age group

Abstract Structural soundness is crucial to improve productivity and longevity of beef cattle in rangeland landscapes. In addition, hair shedding scores are utilized to select for heat tolerant cattle. Thus, the objective of this study was to collect data indicative of cattle adaptability to extensive rangeland landscapes in the Cal Poly beef cattle herd. Three trained technicians assigned claw set, foot angle and hair shedding scores. All data were collected over a 2-day period (n = 3 ranch locations) and foot scores were only collected from females (n = 211) that were at least 1 year of age. Each female was assigned a score for foot angle and claw set (1–9, 5 being ideal). A hair shedding score was also allocated (1–5, 1 = 0% winter coat, 5 = 100% winter coat) to both cows and calves of dams assigned to different age groups. Cattle were retrospectively assigned to a group based on age (Young = 2–3 years of age, Moderate = 4–7 years of age, Old = 8+ years of age) and data were analyzed with the main effects of ranch location and cow age group. Ranch location had no impact (P &amp;gt; 0.05) on foot score or hair shedding score. Cow age group had a significant impact (P &amp;lt; 0.01) on claw set, with young cows exhibiting a lower and more ideal foot score. However, cow age had no effect on hoof angle (P = 0.23). Young cows had a greater (P &amp;lt; 0.001) hair shedding score than their counterparts. Calf hair shedding score was not different (P ≥ 0.23) among dam age groups or ranch locations. Thus, these data indicate that feet and leg structure is compromised as cows age, and younger cows with higher hair shedding scores may lack adaptability to heat stress.

Development of a genetic evaluation for hair shedding in American Angus cattle to improve thermotolerance

BackgroundHeat stress and fescue toxicosis caused by ingesting tall fescue infected with the endophytic fungus Epichloë coenophiala represent two of the most prevalent stressors to beef cattle in the United States and cost the beef industry millions of dollars each year. The rate at which a beef cow sheds her winter coat early in the summer is an indicator of adaptation to heat and an economically relevant trait in temperate or subtropical parts of the world. Furthermore, research suggests that early-summer hair shedding may reflect tolerance to fescue toxicosis, since vasoconstriction induced by fescue toxicosis limits the ability of an animal to shed its winter coat. Both heat stress and fescue toxicosis reduce profitability partly via indirect maternal effects on calf weaning weight. Here, we developed parameters for routine genetic evaluation of hair shedding score in American Angus cattle, and identified genomic loci associated with variation in hair shedding score via genome-wide association analysis (GWAA).ResultsHair shedding score was moderately heritable (h2 = 0.34 to 0.40), with different repeatability estimates between cattle grazing versus not grazing endophyte-infected tall fescue. Our results suggest modestly negative genetic and phenotypic correlations between a dam’s hair shedding score (lower score is earlier shedding) and the weaning weight of her calf, which is one metric of performance. Together, these results indicate that economic gains can be made by using hair shedding score breeding values to select for heat-tolerant cattle. GWAA identified 176 variants significant at FDR < 0.05. Functional enrichment analyses using genes that were located within 50 kb of these variants identified pathways involved in keratin formation, prolactin signalling, host-virus interaction, and other biological processes.ConclusionsThis work contributes to a continuing trend in the development of genetic evaluations for environmental adaptation. Our results will aid beef cattle producers in selecting more sustainable and climate-adapted cattle, as well as enable the development of similar routine genetic evaluations in other breeds.

Physiology and genetics of heat stress in cattle.

Abstract Climatic variables can trigger physiological, biochemical, hematological, and hormonal alterations that influence the maintenance of homeothermy and can affect production and productivity in cattle. An understanding of pathways leading to resistance/tolerance in cattle is necessary, so that the impact of these changes can be mitigated. Particularly, heat stress (HS) has complex effects on the physiology and genetics of production characteristics in animals, thereby making the use of genomic information to select thermotolerant animals difficult. This review looks at physical, physiological, molecular, and genetic aspects of heat tolerance in cattle and the interrelationship between them.

Physiology and genetics of heat stress in cattle

Abstract Climatic variables can trigger physiological, biochemical, hematological, and hormonal alterations that influence the maintenance of homeothermy and can affect production and productivity in cattle. An understanding of pathways leading to resistance/tolerance in cattle is necessary, so that the impact of these changes can be mitigated. Particularly, heat stress (HS) has complex effects on the physiology and genetics of production characteristics in animals, thereby making the use of genomic information to select thermotolerant animals difficult. This review looks at physical, physiological, molecular, and genetic aspects of heat tolerance in cattle and the interrelationship between them.

BREEDING AND GENETICS SYMPOSIUM:Breeding heat tolerant dairy cattle: the case for introgression of the "slick" prolactin receptor variant into dairy breeds.

Increasing environmental temperatures are a threat to the sustainability of livestock production and, because of the high metabolic demands of lactation, to dairy production in particular. Summer heat waves in temperate climates reduce feed intake, milk production, and cow comfort. In extreme heat events, there is an increase in cow mortality. In tropical climates, dairy cattle are mostly (zebu) type or zebu crossbred with temperate dairy breeds. Crossbreeding is undertaken to combine the heat tolerance and tick resistance of zebu with the productivity of temperate dairy breeds. In the absence of improved heat tolerance, milk production and fertility of temperate cattle is severely impaired. We have recently identified a key role for the prolactin pathway in regulating heat tolerance. A de novo mutation in prolactin that impairs prolactin activity was discovered in hairy and heat intolerant, New Zealand dairy cattle. The phenotypes produced were remarkably similar to those seen in fescue toxicosis, a syndrome seen in grazing cattle in the U.S. where ingestion of ergovaline, a fungal toxin from infected pasture, inhibits prolactin secretion. Recognition of the role of prolactin in hairy cattle led us to identify a deletion in exon 10 of the long-form of the prolactin receptor in Senepol cattle that causes truncation of the protein and determines the slick coat and heat tolerance traits found in this , beef breed. The short form of the prolactin receptor is predicted to be unaffected by the deletion. Knowledge of this dominant mutation has provided the impetus to begin a crossbreeding program to investigate performance and heat tolerance of temperate dairy cattle carrying the slick, prolactin receptor variant. The perceived opportunity is to introgress this variant into temperate dairy cattle to enable performance and welfare improvement in hot climates. Heat tolerance of cattle with slick coats appears to be mostly associated with coat type although sweating ability may also be enhanced. Further investigation is required of performance traits in cows homozygous for the slick variant because the published data are almost exclusively from heterozygous animals. Combination of the slick mutation with other favorable genes for heat tolerance, especially those for coat color, will be particularly enabled by gene editing technologies, offering opportunities for further improvement in bovine thermotolerance.

Effect of heat shock protein 70 polymorphism on thermotolerance in Tharparkar cattle.

Aim:Out of various members of heat shock protein (HSP) superfamily which act a molecular chaperon by binding to the denaturing protein thus stabilizing them and preserving their activity, HSP70 are of major importance in thermotolerance development. Thus, present investigation aimed at a screening of HSP70 gene for polymorphisms and possible differences in thermotolerance in Tharparkar breed of cattle.Materials and Methods:A 295 bp fragment of HSP70 gene was subjected to polymerase chain reaction-single-strand conformation polymorphism (SSCP) followed by sequencing of different SSCP patterns in 64 Tharparkar cattle. A comparative thermotolerance of identified genotypes was analyzed using heat tolerance coefficients (HTCs) of animals for different seasons.Results:Three SSCP patterns and consequently two alleles namely A and B were documented in one fragment of HSP70 gene. On sequencing, one single-nucleotide polymorphism with G > T substitution was found at a position that led to a change of amino acid aspartate to tyrosine in allele A. It was found that in maintaining near normal average rectal temperature, genotype AA was superior (p≤0.01). Genotype AA, thus, was found to be most thermotolerant genotype with the highest HTC (p≤0.01).Conclusion:The polymorphism at HSP70 is expected to be a potent determinant for heat tolerance in cattle, which may aid in selection for thermotolerance in cattle.

Association analysis of HSP70A1A haplotypes with heat tolerance in Chinese Holstein cattle

Single-nucleotide polymorphisms (SNPs) in the coding and untranslated regions of heat shock 70kDa protein 1A (HSP70A1A), an inducible molecular chaperone that is responsible for cellular protection against heat stress, have been reported as being associated with heat tolerance. A fragment of the HSP70A1A gene was amplified in Chinese Holstein cattle and eight novel mutations were found. We performed comprehensive linkage disequilibrium (LD) and haplotype analyses of the eight SNPs of the HSP70A1A gene and examined their involvement in heat resistance in 600 Chinese Holstein cattle. Our results revealed the presence of significant differences between individuals carrying haplotype 1 and those without haplotype 1 for most of the heat-tolerance traits. Haplotype 1 increased the risk of heat stress; however, association analysis of its combination with haplotype 2 showed the lowest rectal temperature and red blood cell K(+) level, moderate respiratory rate, and the highest red blood cell NKA level, suggesting a heterozygote advantage in the penetration of the phenotype. Protein expression levels in white blood cells among haplotype combinations further confirmed the hypothesis that heterozygotes for haplotypes 1 and 2 are more sensitive to heat stress. We presume that these mutations may be useful in the future as molecular genetic markers to assist selection for heat tolerance in cattle.

Assessing the heat tolerance of 17 beef cattle genotypes

Cattle production plays a significant role in terms of world food production. Nearly 82% of the world's 1.2 billion cattle can be found in developing countries. An increasing demand for meat in developing countries has seen an increase in intensification of animal industries, and a move to cross-bred animals. Heat tolerance is considered to be one of the most important adaptive aspects for cattle, and the lack of thermally-tolerant breeds is a major constraint on cattle production in many countries. There is a need to not only identify heat tolerant breeds, but also heat tolerant animals within a non-tolerant breed. Identification of heat tolerant animals is not easy under field conditions. In this study, panting score (0 to 4.5 scale where 0=no stress and 4.5 = extreme stress) and the heat load index (HLI) [HLI(BG<25°C) = 10.66 + 0.28 × rh + 1.30 × BG - WS; and, HLI (BG> 25°C) = 8.62 + 0.38 × rh + 1.55 × BG - 0.5 × WS + e((2.4 - WS)), where BG = black globe temperature ((o)C), rh = relative humidity (decimal form), WS = wind speed (m/s) and e is the base of the natural logarithm] were used to assess the heat tolerance of 17 genotypes (12,757 steers) within 13 Australian feedlots over three summers. The cattle were assessed under natural climatic conditions in which HLI ranged from thermonuetral (HLI < 70) to extreme (HLI > 96; black globe temperature = 40.2°C, relative humidity = 64%, wind speed = 1.58m/s). When HLI > 96 a greater number (P < 0.001) of pure bred Bos taurus and crosses of Bos taurus cattle had a panting score ≥ 2 compared to Brahman cattle, and Brahman-cross cattle. The heat tolerance of the assessed breeds was verified using panting scores and the HLI. Heat tolerance of cattle can be assessed under field conditions by using panting score and HLI.

Genetic variation of rectal temperature and its relationship to milk production in Holstein dairy cows

Milk production is significantly decreased by thermal stress. The survival and performance of an animal during heat stress periods depend on several weather factors, especially temperature and humidity. Researchers reported dramatic decreases in milk production as temperature rose above 30 degree of centigrade. Very high environmental temperature is common during the summer months in Iran. Rectal temperature is as indicator of heat tolerance and has been the most frequently used physiological variable for estimating heat tolerance in cattle. Some dairy cows are more heat tolerant and productive when subjected to heat stress. Identification and selection of heat stress resistant cattle offers the potential to increase milk yield in tropical environment. The aim of the present study was to estimate genetic parameters of heat tolerance and its relationship to milk production in Holstein Dairy Cows in Iran.

Características corporais associadas com a adaptação ao calor em bovinos naturalizados brasileiros

O objetivo deste trabalho foi avaliar medidas corporais associadas à tolerância ao calor em bovinos. Utilizaram-se 64 animais das raças naturalizadas Curraleiro (15), Mocho Nacional (7), Crioulo Lageano (7), Pantaneira (14) e Junqueira (11), e 26 animais de duas raças comerciais: Nelore (15) e Holandesa (11). Foram analisados dados sobre comprimento corporal, perímetro de canela, altura de cernelha, perímetro torácico, espessura da pele, espessura do pêlo, número de pêlos, comprimento de pêlos, pigmentação da epiderme e pelame. A raça Curraleiro apresentou menor perímetro torácico, tendo diferido das outras raças, principalmente da Mocho Nacional. As raças Crioulo Lageano e Pantaneira apresentaram maior espessura de pêlo; a raça Mocho Nacional apresentou maior espessura de pele. Os resultados obtidos demonstram que as raças Curraleiro e Junqueira são mais tolerantes ao calor que as demais raças naturalizadas.

Studies of rectal temperature, respiratory rates and heat tolerance in cattle in the humid tropics

ABSTRACTThe rectal temperature and respiratory rates of German Brown, Friesian, German Brown/Friesian crosses, N'Dama and German Brown/N'Dama (BN) crosses were studied with a view to establishing baseline data for cattle in the humid tropical environment of Nigeria.Mean morning (38·62°C) and late afternoon (39·19°C) rectal temperatures for the various breeds were found to differ significantly (P&lt;0·01). However, general breed differences as well as differences between heifers, milking cows, bulls and calves were not significant. Respiratory rates (counts/min) were also significantly higher (P&lt;0·01) in the afternoon than in the morning and appeared related to changes in atmospheric temperature and relative humidity. Breed differences in respiratory rates were also significant, being within the range 17 to 34 in N'Dama, 24 to 43 in BNs and 29 to 51 in the German Brown and Friesian.Heat tolerance indices were very high (89 to 91) for all the breeds studied but showed that the Friesian and German Brown were less heat tolerant than the BNs, and the N'Dama and White Fulani. The results indicate the need to consider diurnal changes in rectal temperature and respiratory rates in the use of these parameters for clinical diagnostic purposes.