Reaction norm models for study genotype × environment interaction in Nellore cattle

Author(s)

Anielly de Paula Freitas

• Document type: Doctoral Thesis
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina de Ribeirão Preto (PCARP/BC)
• Defense date: 2020-10-20

Examining board members

Claudia Cristina Paro de Paz; Mário Luiz Santana Júnior; Ricardo Vieira Ventura

• Advisor: Claudia Cristina Paro de Paz; Maria Eugênia Zerlotti Mercadante

Abstract

The aim of this study was to evaluate the importance of genotype-environment interaction (G×E) and the effects of different selection practices on the environmental sensitivity of reproductive and growth traits in males and females of three Nellore cattle lines [control (NeC), selection (NeS), and traditional (NeT) lines] with different selection goals. Moreover, genetic trends for the intercept and slope were estimated for each line, and the possible reclassification of sires was examined. A total of 9,065 records of weaning weight adjusted over 210 days (W210); 8,208 records of selection weight (SW); 7,799 records of hip height (HH); 3,331 records of scrotal circumference (SC), and 2,311 records of days to first calving (DFC) from Nellore cattle born between 1981 and 2017 at the Advanced Beef Cattle Research Center of the Animal Science Institute /APTA/SAA, Sertãozinho, SP, Brazil, were utilized in the study. (Co)variance components and genetic parameters for all traits were estimated using a standard animal model (AM) and a reaction norm model (RNM) using a reaction norm model using Gibbs sampler. The environmental descriptor adopted were the solutions of contemporary groups (CG). The RNM showed, in general, the best fit for all traits studied. Mean heritability of the studied traits ranged from 0.08 to 0.36 for direct W210 and 0.18 to 0.40 for maternal W210, 0.39 to 0.75 for males and females SW; 0.52 to 0.79 for HH of males and females; 0.46 to 0.68 for SC, and 0.06 to 0.57 for DFC, along the environmental descriptor. The genetic correlations coefficients between intercept and slope ranged from -0.62 to 0.32 for direct W210, -0.29 to 0.10 for maternal W210; 0.03 to 0.81 for SW, -0.19 to 0.63 for HH; -0.14 to 0.39 for SC; and -0.87 to -0.42 for DFC, in all cattle lines. Genetic trends estimated by both AM and intercept of the reaction norm showed gains for the direct effects for the for selected lines for greater postweaning weight differential and a null trend for the NeC line, except for DFC. Genetic trends for the slope and proportion of plastic genotypes indicated that the NeS line was more responsive to environmental changes, whereas the NeC and NeT lines tended to respond more modestly to environmental changes and to be more robust. Reclassification of sires was observed for all traits, specifically in the NeC and NeT lines, because of the weak correlation between the opposite extreme environments. In the NeS line, reclassification of sires was observed for HH and DFC traits. Our results indicate that the effects of genotype by environment interaction are important and should be considered in genetic evaluations of Nellore cattle. Moreover, different selection practices affected the environmental sensitivity of Nellore selection lines tested in this study. (AU)

• FAPESP's process: 16/17517-4 - Reaction Norm models for study genotype x environment interaction in Nellore cattle
• Grantee: Anielly de Paula Freitas
• Support Opportunities: Scholarships in Brazil - Doctorate