Thermoregulatory response of Brangus heifers to naturally occurring heat exposure on pasture

Abstract

Heat stress is a cause of major economic losses to cattle producers, especially in tropical and subtropical environments. The objectives of this study were to assess the phenotypic variability in core body temperature and sweating rate and to evaluate the effect of coat type, temperament, and BW on core body temperature and sweating rate in Brangus heifers. During August and September of 2016, 725 Brangus heifers were evaluated on pasture in four separate groups (n = 200, 189, 197, and 139). Environmental measurements of dry bulb temperature (Tdb) and relative humidity (RH) were measured every 15 min during the entire time of data collection and the temperature-humidity index (THI) was used to quantify heat-stress potential. Coat score, sweating rate, chute score, exit score, and live weight were recorded as the animals passed through the chute. Vaginal temperature was recorded every 5 min for five consecutive days. There was significant variation in vaginal temperature between heifers in the same environmental conditions (σ2u = 0.049), suggesting opportunities for selective improvements. A repeatability of 0.47 and 0.44 was estimated for sweating rate and vaginal temperature, respectively, suggesting that one measurement would be able to adequately describe the sweating capacity or ability to control the body temperature of an individual. Vaginal temperature increased as THI increased, with approximately 1 h lag time in the animal's response. Vaginal temperature (-0.047 °C, P = 0.015) and sweating rate were lower (-5.49 ± 2.12 g/(m2·h), P < 0.01) for heifers that demonstrated a calmer behavior in the chute. Animals with shorter, smoother hair coats had significantly lower vaginal temperatures when compared to animals with longer hair coats (P < 0.01). Also, heavier heifers in this study maintained lower (P < 0.0001) vaginal temperature than the lighter heifers. Our results showed that hair coat, temperament, and weight influenced vaginal temperature regulation.

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

“…There is 1 h lag between the THI and VT, indicating that cows body can withstand environmental heat load for a time and after that body core temperature increases. This 1 h lag is in agreement with a previous report in beef Brangus heifers ( Hamblen et al, 2018 ).…”

“…Surprisingly, cows with high BCS had lower vaginal temperature. In Brangus heifer on summer, Hamblen et al (2018) found that heavier heifers were able to maintain a lower VT relative to lighter weight heifers. The authors suggested that heifers that are better adapted to hot and humid environments tend to have higher average daily gain, what would explain the reduced VT of heavier cows ( Hamblen et al, 2018 ).…”

“…Unexpectedly, non-pregnant cows had as higher VT as late pregnancy cows. Cows with calm behavior shown lower daily VT in relation to the agitated ones ( Hamblen et al, 2018 ). In this trial, the nonpregnant group was composed by 52% of nulliparous and primiparous cows (data no shown), categories known to display agitated temperament in relation to multiparous dairy cows, what may have influenced this group VT.…”

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

“…Thermal tolerance is influenced by many factors, including breed and hair coat properties (Turner and Schleger, 1960;Jenkinson et al, 1975;Gaughan et al, 1999;Olson et al, 2003;Burrow, 2012;Porto-Neto et al, 2014;Barendse, 2017). Differences within and between breeds for thermal tolerance and hair coat properties exist and are indicative of opportunities for improvement through selection (Landaeta-Hernández et al, 2011;Hamblen et al, 2018). Thermotolerance is a quantitative trait controlled by many genes and under environmental influence (Porto-Neto et al, 2014).…”

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

“…Cattle with a shorter-haired coat are able to lose heat more effectively through conductive, convective and radiative cooling at the hair-skin interface (Hansen 2004). Hair length has previously been demonstrated to have a major impact on body temperature (Hamblen et al 2018) and has a high heritability (0.67 and 0.42 for undercoat and topcoat respectively) (Sarlo Davila et al 2019), indicating that this trait is largely influenced by genetics. The objective of this study was to identify genetic variants associated with the length of the undercoat and topcoat of cattle.…”