Adaptability in tropical beef cattle: genetic parameters of growth, adaptive and temperament traits in a crossbred population

Abstract

Adaptability in tropical beef cattle can be assessed by measurable traits such as growth under the influence of environmental stressors, by parasite resistance as measured by indicator traits such as tick counts (TICK) and faecal egg counts of worms (EPG), by heat resistance as measured by indicator traits such as rectal temperatures (TEMP) and coat scores (COAT) and, to a certain extent, temperament of the animal as measured by flight time (FT). Data from a crossbreeding experiment involving various genotypes derived from tropically adapted British, Sanga-derived, Zebu cross, Zebu and Continental beef cattle breeds were analysed to estimate variance components and genetic parameters of growth, adaptive and temperament traits. Breed group differences were accounted for by including fractional coefficients of direct and maternal additive and dominance genetic effects as covariates. In the univariate analyses, 6 models were compared ranging from the simplest model with animal as the only random effect to the full model comprising direct and maternal additive genetic variance and their covariance and the permanent environment effect due to dam (growth traits) and animal (adaptive and temperament traits). The heritability estimates were 0.41, 0.21, 0.19, 0.28, 0.41 and 0.15 for birth weight (BWT), weaning weight (WWT), preweaning average daily gain (PREADG), yearling weight (YWT), final weight at about 18 months of age (FWT) and post-weaning average daily gain (POADG), respectively. The maternal component of additive genetic variance as a proportion of phenotypic variance in BWT, WWT and PREADG was 0.15, 0.10 and 0.10, respectively. The heritability estimates for TICK, EPG, TEMP, COAT and FT were 0.13, 0.24, 0.12, 0.26 and 0.20, respectively. High positive genetic and phenotypic correlations were observed among growth traits. Low (insignificant) genetic correlations were observed between TICK, EPG and growth traits. However, genetic correlations between growth traits and heat tolerance traits (TEMP and COAT) were moderately negative implying that as the ability of an animal to handle heat stress increases, growth also increases at the genetic level. Genetic correlations among TICK, EPG and TEMP were moderately positive, suggesting that closely-linked genes affect these adaptive traits. The significant negative genetic relationship between TEMP and FT suggests that cattle with high heat resistance have desirable temperament. With the increasing crossbred populations in the northern Australian beef cattle industry, the best breeding strategy should aim to exploit both crossbreeding and within population selection to make improvements in growth, adaptive and temperament traits to increase overall productivity of the enterprise.

Genetics of adaptive traits in heifers and their relationship to growth, pubertal and carcass traits in two tropical beef cattle genotypes

“…The low h 2 of TICK in the present study was comparable to those reported in a crossbred population (Prayaga and Henshall 2005), even though the later estimate was derived from repeated tick counts. However, the current h 2 estimates of TICK and FLY were lower than estimates reported by Burrow (2001) The data for EPG and FT are transformed; genetic parameters not reported where n < 600. a composite population.…”

“…One of the reasons for these lower estimates of h 2 could be relatively low tick and fly challenge during the present study, compared with higher challenges in the earlier study (Burrow 2001). Moderate h 2 estimates for EPG were comparable to those in earlier studies (Burrow 2001;Prayaga and Henshall 2005). The immune response of ruminants changes with the age of the host, the length of the exposure of host to parasites, the number of parasites and plane of nutrition (Wakelin 1989;Gray and Gill 1993).…”

“…Some recent studies have focussed on crossbred (Prayaga and Henshall 2005) and composite populations (Burrow 2001). Most studies were based on a specific region (Central Queensland) of northern Australia and thus did not represent the whole of tropical Australia.…”

A genome-wide association study of tick burden and milk composition in cattle

“…In cattle, zebu have greater growth rates and performance in the presence of parasites, in hotter climates and fed lower quality feed than taurine animals, but poorer growth rates and performance in the absence of parasites, in cooler climates and fed better quality feed Vercoe 1977, 1984). However, these might represent breed genetic differences because genetic correlations for growth traits and parasite resistance traits are often close to zero when analysed within a breed (Prayaga and Henshall 2005;Prayaga et al 2009).…”

Reatividade animal

“…Portanto, a alta reatividade tem efeito potencializador sobre a resposta comportamental tornandoa mais intensa quanto mais reativo for o animal. Devido a isto, animais mais reativos têm menor capacidade adaptativa às mudanças ambientais e são mais susceptíveis aos agentes estressantes, logo ao desencadeamento e desenvolvimento do processo de estresse (Grandin, 1997(Grandin, , 1998Prayaga, 2003;Prayaga & Henshall, 2005;Prayaga et al, 2006). É relevante mencionar que o entendimento do mecanismo de estresse em bovinos, assim como em outras espécies domésticas, torna-se importante quando se deseja evitar o sofrimento dos animais submetidos aos diversos sistemas de criação.…”