Reaction norms for the study of genotype-environment interaction for growth and indicator traits of sexual precocity in Nellore cattle

Abstract

ABSTRACT. The objective of this study was to quantify the magnitude of genotype-environment interaction (GxE) effects on age at first calving (AFC), scrotal circumference (SC), and yearling weight (YW) in Nellore cattle using reaction norms. For the study, 89,152 weight records of female and male Nellore animals obtained at yearling age were used. Genetic parameters were estimated with a single-trait randomregression model using Legendre polynomials as base functions. The heritability estimates were of low to medium magnitude for AFC (0.05 to 0.47) and of medium to high magnitude for SC (0.32 to 0.51) and YW (0.13 to 0.72), and increased as the environmental gradient became more favorable. The genetic correlation estimates ranged from 0.25 to 1.0 for AFC, from 0.71 to 1.0 for SC, and from 0.42 to 1.0 for YW. High Spearman correlation coefficients were obtained for the three traits, ranging from 0.97 to 0.99. The reaction norms along the environmental gradient of 10 sires each with the highest or lowest breeding value for YW predicted by single-trait analysis demonstrated more plastic phenotypes for YW and more robust phenotypes for SC. The effect of GxE was most important for YW and AFC with respect to SC. When animals are selected for higher SC or YW or lower AFC, considering or not the GxE effect, it is expected that the same animals will be selected. The reaction norms obtained based on sire breeding values along the environmental gradient showed that animals with extreme breeding values respond differently as environmental conditions improve.

Genotype–environment interaction for age at first calving in buffaloes, using the reaction norm model

“…Chiaia et al () reported estimates of correlation between extreme environments up to −0.270 for AFC, while in this study all values found were higher. Lemos et al () found values up to 0.250 between extreme environments, similar to that verified with the GAFC gradient. The low genetic correlation among extreme environments suggests that different groups of genes were expressed in each environment, mainly for GMY.…”

Reaction norm for yearling weight in beef cattle using single-step genomic evaluation1

“…This indicates that variations in the EG influenced the phenotypic expression of YW. Lemos et al (2015) observed more pronounced changes in EBV ranking for Nellore using YW in a three-trait reaction norm model.…”

“…In the two steps, the authors reported heritability estimates between 0.08 and 0.23 evidencing G × E. Pegolo et al (2011) studied G × E for weight at 450 d in Nellore cattle and observed moderate heritability estimates of 0.20-0.39 in the intermediate and the most favorable environment groups, respectively. However, Lemos et al (2015) investigated YW in Nellore cattle using a three-trait reaction norm model and reported higher heritability estimates varying from 0.13 to 0.72 in EG. The difference observed between the results found in this study and those reported in the literature is possibly because of the methodology, the way EG were defined, and the number of observations in each EG.…”

The Current Status of Indigenous Ovine Genetic Resources in Southern Africa and Future Sustainable Utilisation to Improve Livelihoods

“…The first three measurements are a good indication of growth, whereas scrotal circumference indicates ram fertility and may be an indicator of its daughters' reproductive performance [25]. In cattle, scrotal circumference is favourably correlated to the age at first calving [26]. The mature live weight for Zulu ewes and rams is 32 and 38 kg, respectively, which is small compared to the commercial breeds.…”