Alternative Models in Genetic Analyses of Carcass Traits Measured by Ultrasonography in Guzerá cattle: A Bayesian Approach

Abstract

<p class="4Body">The objective was to study alternative models for genetic analyses of carcass traits assessed by ultrasonography in Guzerá cattle. Data from 947 measurements (655 animals) of Rib-eye area (REA), rump fat thickness (RFT) and backfat thickness (BFT) were used. Finite polygenic models (FPM), infinitesimal polygenic models (IPM) and FPM combined with IPM (IPM + FPM) were empirically tested, adjusting for the effects of permanent environment, age and weight at measurement and the contemporary group. A Bayesian analysis using the computer package FlexQTL^TM was adopted. The combined model adjusted to the data, allowing reliable genetic analyses of REA and BFT. For the RFT, the IPM model was the only one to have convergence and, in this case, the trait should be analyzed by a polygenic model. The presence of up to three major genes (MGs) controlling the expression of REA and two MGs for BFT was detected. The additive genetic action was over dominance to REA, and for BFT the dominance genetic action was greater. Heritability estimates, and respective standard error, adjusted for the combined model to REA were 0.15 (0.00025) for the polygenic fraction and 0.10 (0.00019) for the oligogenic fraction; for BFT was 0.19 (0.00027) and 0.13 (0.00025), respectively. Heritability of 0.17 (0.00028) was estimated for RFT when the model was adjusted to IPM. There are major genes segregating within the population studied for REA and BFT traits, thus, their genetic analyses must be studied considering oligogenic effects. The major gene effects detected for a small number of genes, may possibly help to increase the reliability in detecting chromosomal regions that explain and control the phenotypic expression of these traits, facilitating research on detection and validation of molecular markers in this population.</p

Research Article Estimation of variance components for carcass and production traits in Guzerat cattle

“…Estimations for our study included 1,395 animals for REA, 908 for BFT, 955 for RFT and 978 for IMF. Junior et al (2013), using a Bayesian approach for studying alternative models for genetic analyses of these traits, measured by ultrasound, in Guzerat found heritability estimates of 0.15, 0.19 and 0.17 for REA, BFT and RFT respectively, considering a polygenic model.…”

“…Furthermore, at the beginning of the past century, the females were submitted to intense crossbreeding schemes to obtain the synthetic Indubrasil breed, decreasing up to 50% the number of females for the replenishment of the breed in 1992 (Faria et al, 2004). Nevertheless, the Guzerat breed has made a great contribution to Brazilian cattle production, improving productivity, hardiness, precocity and meat quality (Junior et al, 2013). Traits such as rib-eye area, backfat and rump fat thickness, intramuscular fat percentage and visual score for finishing have been continuously assessed in breeding programs because they are related to meat quality, carcass yield and cutability, and organoleptic properties (Bergen et al, 2005;Neto et al, 2009;Junior et al, 2013;Cafe et al, 2018), while other traits such as dry matter intake, average daily gain, metabolic weight, residual feed intake and margin are related to production efficiency (Basarab et al, 2003;.…”

“…Nevertheless, the Guzerat breed has made a great contribution to Brazilian cattle production, improving productivity, hardiness, precocity and meat quality (Junior et al, 2013). Traits such as rib-eye area, backfat and rump fat thickness, intramuscular fat percentage and visual score for finishing have been continuously assessed in breeding programs because they are related to meat quality, carcass yield and cutability, and organoleptic properties (Bergen et al, 2005;Neto et al, 2009;Junior et al, 2013;Cafe et al, 2018), while other traits such as dry matter intake, average daily gain, metabolic weight, residual feed intake and margin are related to production efficiency (Basarab et al, 2003;. Traditionally, genetic breeding programs in Brazil have only considered traits related to reproduction and adaptability; more recently these programs have included carcass characteristics, mainly in Nellore, with the aim to predict the genetic merit and expected progeny differences (Neto et al, 2009), but Guzerat has remained sidelined in this area.…”