Genetic parameters of growth traits in Cuban Zebu through the multi-trait animal model and reaction norm model

Resumen

A multi-trait animal model (15,904 data) and a reaction norm model
(13,068 data) were studied, in order to estimate genetic parameters and
environmental awareness of the weight at 18 months (P18) and (TDG)
of Cuban Zebu during the performance test for future sires. The animals
were born between 1981 and 2012 and were the offspring of 295 parents.
Multi-trait animal model allowed to obtain the solutions of fixed
effect of from the group of contemporaries, heritabilities and genetic
tendencies of P18 and trial daily gain TDG. Later, a reaction norm
model of sire type was considered, with the group of contemporaries
(herd-year-three-month period of animal birth) as fix effect the effect
of random regression of sire (cubic, square and linear Legendre polynomials)
through an environmental gradient, expressed as solution of
fix effect, so a total of 6 environmental classes were created. Estimated
values of heritability, through the animal model, were 0.20 ± 0.02 and
0.28 ± 0.02 for TDG and P18, respectively, with a genetic correlation
of 0.94 among them. Using the reaction norm model, the estimates
varied from 0.13±0.04 to 0.43±0.08, and the highest corresponded
to favorable environments or positive gradients. Correlation values,
very close to 1, indicate the non-existence of genotype x environment
interaction in most of the cases. However, there may be correlations
lower than 0.8 in the most unfavorable environment, which indicates
that sires selected in favorable environments may not have the same
performance after passing to unfavorable environments.

Key words: Performance test, genetic correlation, environmental
gradient