Heritability and genotype-environment interactions for growth curve parameters in meat-type quail fed different threonine:lysine ratios from hatching to 21 d of age.

The aim of the present study was to estimate heritabilities and evaluate the existence of genotype-environment interactions for growth curve parameters in quail fed diets containing different threonine:lysine ratios. A total of 4,441 body weight information from two genetic quail groups (LF1 and LF2) fed diets containing 0.66%, 0.71%, 0.76%, 0.81%, and 0.86% threonine:lysine ratios from hatching to 21 d of age were evaluated. From 22 to 35 d of age, quail received a single diet. The Gompertz model was used to estimate growth curve parameters. Genetic analyses were performed using random regression models, by Legendre polynomials of the second kind, considering homogeneity of residual variances. The following characteristics were evaluated: asymptotic weight, asymptotic growth rate, and inflection point. Increases in threonine:lysine ratios promoted higher heritability estimates for these variables in the LF1 genetic group compared to LF2, which indicates that the additive genetic variation was modified due to the environmental variation influenced by the evaluated amino acid ratios, with differences between both genetic groups. Thus, it is recommended that quail be selected in the 0.86% ratio in genetic group LF1 and 0.66% in genetic group LF2, where greater heritabilities were observed. Dispersion of individual breeding values along the environmental gradient was observed for all evaluated characteristics, in both genetic groups, suggesting the existence of genotype-environment interactions for these variables. The evaluated amino acid ratios should be considered in quail breeding programs, since breeding value predictions for a determined threonine:lysine ratio are not valid for other ratios.

Estimação de valores genéticos para codornas europeias em função dos níveis da relação treonina: lisina da dieta: do nascimento aos 21 dias de idade / Estimation of breeding values for European quails in function of threonine: lysine ratios of diet: from birth to 21 days of age

O presente trabalho foi realizado com o objetivo de avaliar a sensibilidade dos valores genéticos dos pesos corporais e as características de carcaças de codornas europeias às mudanças do gradiente ambiental (níveis da relação treonina com a lisina das dietas), do nascimento aos 21 dias de idade, por meio de modelos de regressão aleatória com diferentes classes de variância residual. Os dados utilizados neste estudo são provenientes de 915 codornas de corte da linhagem LF1 e 839 da linhagem LF2, pertencentes ao Programa de Melhoramento Genético da Universidade Federal dos Vales do Jequitinhonha e Mucuri. Foram avaliados os pesos corporais e os rendimentos da carcaça das aves. As sensibilidades dos valores genéticos às mudanças nos níveis da relação treonina:lisina (interação genótipo x ambiente) foram obtidas por modelos de regressão aleatória (utilizando normas de reação) por meio do programa Wombat, que utiliza o princípio da máxima verossimilhança restrita (REML). O modelo de regressão aleatória que considerou duas classes de variância residual foi o mais indicado para a maioria das análises realizadas. Verificaram-se alterações na classificação dos valores genéticos para as duas linhagens de codornas de corte estudadas. Esse comportamento indica sensibilidade de valores genéticos aditivos às mudanças nutricionais, o que caracteriza a existência de interação genótipo x ambiente. A predição dos valores genéticos deve ser feita com o mesmo nível da relação treonina:lisina da dieta com a qual as codornas serão alimentadas no sistema de produção.(AU)

This research was carried out to evaluate the sensitivity of breeding values of body weight and carcass traits in two lines of European quails (LF1 and LF2) to changes in the environment gradient (levels of threonine: lysine ratio of diets) from hatch to 21 days of age in two lines LF1 and LF2 using Random Regression Models with different classes of residual variance. Records are from 915 quails of line LF1 and 839 of line LF2 belonging to the Breeding Improvement Program of Universidade Federal dos Vales do Jequitinhonha e Mucuri. Live body weight and weights and yields of carcass, breast, and thigh and drumstick were measured. The sensitivities of breeding values to changes in threonine: lysine ratios (genotype x environment interaction) of diets were obtained by random regression models (reaction model) using the WOMBAT program using the Restricted Maximum Likelihood principle. Model considering two classes of residual variance showed the best goodness of fit. The Reaction Norms analyses indicated changes in the ranking of breeding values for both lines suggesting quails selected in one level of threonine: lysine ratio will not express all their genetic potential if fed different threonine: lysine ratio diets. This behavior indicates sensitivity of breeding values to changes in the nutrition characterizing the genotype by environment interaction. The prediction of breeding values must be performed using the same level of threonine: lysine ratio in diet the quails will be fed in the production system.(AU)