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

Abstract

Thermal stress in hot humid conditions limits cattle production. The objectives for this study were to estimate genetic parameters for hair characteristics and core body temperature under low and high temperature humidity index (THI) conditions. Hair samples were collected and measured for length and diameter. Core body temperature was measured as vaginal temperature every 15 min over a 5-d period using an iButton temperature measuring device implanted in a blank CIDR in 336 heifers from the University of Florida multibreed herd (ranging from 100% Angus to 100% Brahman). Restricted maximum likelihood procedures were used to estimate heritabilities from multiple bivariate animal models using the WOMBAT program. Estimates of heritability for hair diameter, undercoat length, topcoat length, body temperature under low THI conditions, and body temperature under high THI conditions were 0.50, 0.67, 0.42, 0.32, and 0.26, respectively. The genetic parameters estimated in this study indicate a large, exploitable genetic variance which can be selected upon to improve tolerance in cattle. Breed effects for differing compositions of Brahman and Angus were also estimated. As Brahman breed composition increased by 25% undercoat length, topcoat length, body temperature under low THI conditions, and body temperature under high THI conditions decreased by 1.32 mm, 2.94 mm, 0.11 °C, and 0.14 °C, respectively. Under both low and high THI conditions, cattle with 25% Brahman breed composition or greater maintained a significantly lower body temperature than the 100% Angus breed group. The incorporation of Brahman germplasm is recommended for herds that often experience heat stress conditions in order to increase resilience to heat stress.

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

“…The heritability of body temperature under low THI conditions (h 2 = 0.32 ± 0.18) has been reported to be slightly higher than that of body temperature under high (h 2 = 0.26 ± 0.16) THI conditions (Sarlo-Davila et al, 2019), which is consistent with our results showing that heritability for AMRT were higher than for PMRT. The higher estimates in heritability reported by Sarlo-Davila et al (2019) compared with the present study might be due to the use of RT (this study) rather than vaginal temperature (potentially different traits) and measurements in dairy cows (this study) rather than beef cattle (Howard et al, 2014), which is an important factor considering that genetic parameters are population specific. Furthermore, the permanent environmental variance and repeatability of PMRT is similar to that of AMRT.…”

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

“…On pregnant Brahman-Angus cows on summer, animals with 4/8 or more of Brahman genetic composition, a zebu breed, had lower daily VT than the groups with lower Brahman genetic ( Dikmen et al, 2018 ). On Brahman-Angus heifers, animals 1/4 Angus had no difference of VT than 1/2 Angus heifers, but had lower VT than Angus heifers (80% to 100% Angus) ( Davila et al, 2019 ).…”

“…Zebu cattle are more adapted for body temperature regulation under heat stress, among other factors, due to the short coat length, size and number of sweat glands ( Hansen, 2004 ). Coat length in Brahman-Angus cows decreases as zebu influence increases over than 1/2 and show high heritability ( Davila et al, 2019 ). The reduced thermoregulation capacity showed by 3/4 and 7/8 Girolando cows in this trial may be due to reduced presence of zebu genes related to thermorregulation traits.…”

“…Vaginal temperature (VT) monitoring is a precise technique to evaluate body core temperature continuously without effect of restraint stress observed on rectal temperature measurement, the classic way to evaluate body temperature in cattle ( Vickers et al, 2010 and Burfeind et al, 2012 ). Studies have evaluated daily body core temperature variation by VT monitoring in Holstein cows ( Kendall et al, 2009 ; Nabenishi et al, 2011 ) and crossbred beef cows ( Dikmen et al, 2018 ; Davila et al, 2019 ) exposed to induced or natural heat stress. However, there are no reports of daily VT response of crossbred dairy cows to natural heat stress on tropical and subtropical conditions.…”

Incorporating Brahman Genetics in the Cow Herd to Alleviate Heat Stress

“…Brahman cattle have dark skin pigmentation that protects against UV damage from solar radiation. They also have short hair coats (on average, 10 mm shorter than Angus [Sarlo Davila et al 2019]) that are light colored and reflect radiative heat, which help them to remain cooler. This short hair coat also helps cattle sweat more effectively.…”