Avaliação genética de bovinos Guzerá utilizando-se a produção de leite e de gordura no dia do controle

Abstract

Dados referentes a 467 lactações e 5.604 controles de bovinos da raça Guzerá, controladas entre 1987 e 2004, foram utilizados com objetivos de se estimar os parâmetros genéticos e predizer os valores genéticos para a produção de leite (PLDC) e de gordura (PGDC) no dia do controle, e comparar a classificação dos animais por estimativas obtidas mediante análises unicaracterísticas. A PLDC e PGDC foram analisadas através de um modelo animal, em análises unicaracterísticas, considerando-se as quatro primeiras lactações. Os modelos estatísticos para analisar as PLDC e PGDC incluíram os efeitos genéticos aditivos diretos e de ambiente permanente, como aleatório, o efeito fixo de grupo contemporâneo, formado pelo ano e mês do controle, e a idade da vaca ao parto como co-variável, regressão linear e quadrática. De maneira geral, as herdabilidades estimadas foram maiores no início e no final da lactação, indicando possibilidade de resposta à seleção. As correlações de ordem entre os valores genéticos para Podução de Leite Total e Podução de Gordura Total e as PLDC e PGDC, foram maiores no início e metade da lactação que as do final. A seleção para PLDC e PGDC no início e final da lactação pode ser indicada como critério de seleção, em substituição à produção total. Palavras-chave: parâmetros genéticos, produção de leite, seleção Genetic evaluation of Guzerá cows using test day milk and fat yield ABSTRACT Data from 467 lactations of 5.604 controls of bovine of the Guzerá cows, controlled between 1987 and 2004 were used with the objectives to estimate the genetic parameters and to predict the genetic values for the production of milk (PLDC) and fat (PGDC) and to compare it with the classification of the animals, for estimates obtained by ordinary test-day model. PLDC and PGDC were analyzed through an animal model, considering the first four milk yield (repeatibility model). The statistical models to analyze PLDC and PGDC included the addictive genetic direct effects and of permanent of ambient, like random, the fixed effect of contemporary group, formed by the year and the month of control, and the age of the cow at delivery as co-variable, linear and quadratic regression. In a general way, the estimaded herdabilidades were higher in the beginning and at the end of the lactation, indicating possibility to the selection. The correlation order among the genetic values for production of total milk and production of total fat and PLDC and PGDC were greater in the beginning and half of the lactation that the one at the end. The selection for PLDC and PGDC in the beginning and end of the lactation it can be indicated as selection criterion, in substitution to the total production.

Bos indicus or Bos taurus mitochondrial DNA - comparison of productive and reproductive breeding values in a Guzerat dairy herd

“…The phenotypic LMY and DIM performances observed in this study were close to those observed in other studies with the Guzerat breed (Cobuci et al, 2000;Martinez et al, 2000;Cruz et al, 2006).…”

“…In the analysis of milk yield, some authors have used comparable statistical models, but without considering the inbreeding coefficient as a covariate (Cobuci et al, 2000;Cruz et al, 2006;Peixoto et al, 2006). In the present study, since there were a great number of inbred animals in the herd, the inclusion of the inbreeding coefficient was necessary for the adjustment of the estimated breeding values of highly inbred cows or bulls with highly inbred daughters.…”

“…In the same paper, these authors presented results from other studies, with estimates varying from 0.25 to 0.38 in the Jersey breed. Cruz et al (2006) estimated the value 0.13 for the heritability coefficient for milk yield in the Guzerat breed, however, using a production file with a reduced number of records. Cobuci et al (2000) estimated values from 0.16 to 0.23 and Peixoto et al (2006) estimated the value of 0.23, both for the heritability coefficients of milk yield in the Guzerat breed.…”

Genetic parameters for test-day milk yield, 305-day milk yield, and lactation length in Guzerat cows

“…In this respect, whereas some animals have good milk yield persistence, others reduce, or even cease, production early in lactation. Cruz et al (2006), who also studied TDMY in Guzerat cows, observed a similar trend of variance components during the early period of lactation, including the observation of higher heritabilities compared to midlactation. However, the range of heritability values was wider (from 0.03 in the fifth month to 0.29 in the eighth and tenth months).…”