Avaliação da produção de leite em cabras da raça Saanen utilizando modelos de regressão aleatória / Saanen goats milk yield evaluation using random regression models

AUTOR(ES)

Gilberto Romeiro de Oliveira Menezes

DATA DE PUBLICAÇÃO

2008

RESUMO

Data from 10,238 weekly milk yield records from 388 first lactations of Saanen goats were used to evaluate the persistency of lactation under a random regression model. First, five models were compared (W035, W05, W0565, W068 e W10) generated by modifications of Wilmink function, assuming homogeneity of residual variance along the lactation. The value -0.05 was kept on model W05 while models W035, W0565, W068 e W10 used values -0.035, -0.0565, -0.068 e -0.10, respectively, in replacement to -0.05 value. After choosing the best model, six structures were evaluated for residual variance: homogeneity, two classes, three classes, four classes, five classes and six classes along the lactation. Subsequently, six different measures of persistency of lactation, adapted from those used on dairy cattle, obtained by replacing bovine reference values to goats ones on the expressions. AIC, BIC, ln L criterions and likelihood ratio test (nested models) were used on models evaluation. Model W035 presented the best fit among the evaluated ones. Relating to residual variance, the most indicated by used criterions was the structure of six classes. By presenting less genetic correlation with milk yield until 268 days (0.14), the persistency measure (PS4) obtained by the sum of genetic values, on period from 41st to 240th day of lactation, as deviations of yield at 40 days of lactation may be pointed for genetic evaluations. Because of the low heritability of this measure (0.03), few responses from selection are expected on this herd.

ASSUNTO(S)

milk genetica e melhoramento dos animais domesticos caprino leite goat persistency persistência

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