Influência do intervalo de idade na composição de grupos contemporâneos para avaliação genética de ingestão de matéria seca em bovinos da raça Nelore

Abstract

The objective of this study was to evaluate the influence of age range on the composition of contemporary groups (GC) for genetic evaluation of dry matter intake (IMS) in Nellore cattle. Data from Nellore cattle from farms participating in the Nelore Brasil Program of the National Association of Breeders and Researchers (ANCP), from 2012 to 2018, were used. Data on dry matter intake were obtained from 46 feed efficiency tests. performed in electronic trough systems. It was considered as evaluation criterion different scenarios of contemporary animal groups being characterized by three distinct age ranges: (I) contemporary group consisting of animals with age range up to 90 days; (II) contemporary group consisting of animals up to 60 days old, and (III) contemporary group consisting of animals up to 30 days old. In scenario I, we observed a smaller number of contemporary groups (76) compared to scenarios II and III, which obtained 95 and 156 groups, respectively. It was also found that the reduction in the age range of the animals led to an increase in the amount of CG, together with a decrease in the number of animals within the CG. Scenario I and III presented 13 and 40 CG with up to 10 animals, respectively. By observing the amount of GC with more than 80 animals, scenario II contained only two GC, while scenarios I and II had 15 and 16 GC, respectively. The variance and heritability components, as well as the genetic values for dry matter intake (IMS) were predicted by one-trait analyzes under animal model using Bayesian statistics using the Multiple Trait Gibbs Sampler for Animal Models (MTGSAM) application. The accuracy of expected progeny differences (DEPs) was calculated according to the BIF (Beef Improvement Federation). In the Gibbs sampler application, an initial chain size of 300,000 cycles was used, and the first 50,000 cycles were discarded and samples taken every 1,000 cycles, totaling 250 samples of variance components and genetic parameters. Similarity was observed in all variance components and genetic parameters when comparing the results between the different scenarios. However, it can be observed that the scenario II presented a formation of CG that tends to a greater sensitivity in the identification of the parameters of the genetic evaluations. To verify possible changes in the classification of the animals, based on the comparison of the genetic values obtained from the different formations of contemporary animal groups, the rank correlation or Spearman was used. It can be concluded that there was no influence of age range on the composition of contemporary groups for genetic evaluations of IMS, since all scenarios evaluated are efficient in controlling environmental interference.