Estimation of genetic parameters of milk and fat yield of Brown-Swiss cows using frequentist and bayesian methodologies / Estimação de parâmetros genéticos de produção de leite e de gordura da raça Pardo-suíça, utilizando metodologias freqüentista e bayesiana

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

First lactation data of 6.262 Brown-Swiss cows from 311 herds, daughters of 803 sires with calving between 1980 and 2003 were used to estimate genetic parameters for milk and fat production traits. The components of variance were estimated by restricted maximum likelihood (REML) and bayesian methods, using animal model with uni and two-traits analisys . The estimation by REML was obtained with the software MTDFREML (BOLDMAN et al. 1995) testing unitrait models with different effects to covariables and considering contemporary group and season as fixed effect. The best fitting obtained on unitrait analisys were used on two-trait analisys. The estimative of additive variance was reduced when lactation length was included on the model suggesting that the animals were been fitted to the same base on the capacity of transmit a longer or shorter lactation length to the progeny. Therefore, fitting to this covariable is not recommended. On the other side, the age of calving has linearly influenced milk and fat production. The heritability estimates were 0,26 and 0,25 to milk and fat yield respectively with genetic correlation of 0,95. the high correlation among these traits suggests that part of genes that acts on milk yield also respond to fat yield, in such way that selection for milk yield results, indirectly, in increase on fat yield. The estimation by Bayesian inference was made on software MTGSAM (VAN TASSELL E VAN VLECK, 1995). Chain lengths were tested to obtain the marginal posterior densities of unitrait analisys, the best option of chain length, burn-in and sampling interval was used on two-trait analisys. The burn-in periods were tested with the software GIBANAL (VAN KAAM, 1998) witch analysis inform a sampling interval for each burn-in tested, the criteria for choosing the sampling interval was made with the serial correlation resulting by burn-in and sampling process. The heritability estimates were 0,33 0,05 for both traits with genetic correlation of 0,95. Similar results were obtained on studies using the same methodology on first lactation records. The stationary phase adequately reached with a 500.000 chain length and 30.000 burn-in iteractions.

ASSUNTO(S)

gibbs sampler bovino de leite reml restricted maximum likelihood dairy cattle teoria bayesiana amostrador de gibbs máxima verossimilhança restrita bayesian theory reml genetica e melhoramento dos animais domesticos

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