Comparação entre critérios de seleção de precocidade sexual e a associação destes com características de crescimento em bovinos Nelore
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Data
2001-02-01
Autores
Ortiz Peña, Carlos Dario
Queiroz, Sandra Aidar de [UNESP]
Fries, Luiz Alberto [UNESP]
Título da Revista
ISSN da Revista
Título de Volume
Editor
Sociedade Brasileira de Zootecnia
Resumo
Neste trabalho estimaram-se parâmetros genéticos do perímetro escrotal (PE), PE corrigido para idade (PEi) e PEi corrigido para peso corporal (PEip) de bovinos Nelore, comparando-se a classificação dos animais pelas DEPs, segundo o critério adotado. Além disso, estimaram-se a correlação genética existente entre as três expressões do PE e o ganho médio diário pré-desmama, o ganho médio diário pós-desmama, o número de dias para ganhar 160 kg após o nascimento e o número de dias para ganhar 240 kg após a desmama. As informações foram obtidas nos Registros de Produção da Associação Paraguaia dos Criadores de Nelore, entre 1986 e 1997, em 110 rebanhos. As estimativas dos componentes de variância e herdabilidade foram obtidas pelo Método da Máxima Verossimilhança Restrita, usando modelos animais uni característica. As herdabilidades estimadas foram 0,41; 0,40; e 0,47 para PE, PEi e PEip, respectivamente, todas indicando possibilidade de progresso genético por seleção. A estimativa de correlação genética entre PEi e PEip (0,62) foi moderada e os valores obtidos para as correlações entre as características de precocidade sexual e de crescimento foram de pequena magnitude. As estimativas de correlações de rank das DEPs foram 0,98 para PE e PEi e 0,59 para PEi e PEip. Os resultados evidenciaram a ocorrência de mudanças na classificação dos melhores animais, quando se considerou ou não o peso vivo na correção do PE. A utilização do perímetro escrotal corrigido para idade e peso corporal como critério de seleção evitaria ou reduziria a resposta correlacionada com tamanho adulto superior, trazendo maiores progressos genéticos na precocidade sexual.
In this study genetic parameters of scrotal circumference (SC), SC corrected for age (SC/a) and SC/a corrected for live weight (SC/aw) of Nellore Cattle were estimated and comparisons of the rank based on EPDs of the above criteria were made. In addition, the genetic correlations between SC measurements and growth (preweaning average daily gain, number of days to gain 160 kg after birth, post weaning average daily gain and number of days to gain 240 kg after weaning) were estimated. The information came from the Paraguayan Nellore Breeders Association Production Registry, obtained from 1986 to 1997, in 110 herds. Restricted Maximum Likelihood using one-trait animal models were used to obtain the variance components and heritability estimates. The heritability estimates were 0.41, 0.40, and 0.47 for SC, SC/a and SC/aw, respectively, all of them indicating the possibility of genetic improvement by selection. The estimate of genetic correlation between SC/a and SC/aw (0.62) was moderate and the obtained values for the correlations between the sexual precocity and growth traits were of small magnitude. The rank correlations between EPDs estimates were 0.98 for SC and SC/a and 0.59 for SC/a and SC/aw. The results showed changes in the classification of animals selected when live weight was or was not considered in the SC correction. The selection criterion scrotal circumference corrected for age and live weight (SC/aw) could reduce a correlated response with larger adult size, while obtaining substantial improvement in sexual precocity.
In this study genetic parameters of scrotal circumference (SC), SC corrected for age (SC/a) and SC/a corrected for live weight (SC/aw) of Nellore Cattle were estimated and comparisons of the rank based on EPDs of the above criteria were made. In addition, the genetic correlations between SC measurements and growth (preweaning average daily gain, number of days to gain 160 kg after birth, post weaning average daily gain and number of days to gain 240 kg after weaning) were estimated. The information came from the Paraguayan Nellore Breeders Association Production Registry, obtained from 1986 to 1997, in 110 herds. Restricted Maximum Likelihood using one-trait animal models were used to obtain the variance components and heritability estimates. The heritability estimates were 0.41, 0.40, and 0.47 for SC, SC/a and SC/aw, respectively, all of them indicating the possibility of genetic improvement by selection. The estimate of genetic correlation between SC/a and SC/aw (0.62) was moderate and the obtained values for the correlations between the sexual precocity and growth traits were of small magnitude. The rank correlations between EPDs estimates were 0.98 for SC and SC/a and 0.59 for SC/a and SC/aw. The results showed changes in the classification of animals selected when live weight was or was not considered in the SC correction. The selection criterion scrotal circumference corrected for age and live weight (SC/aw) could reduce a correlated response with larger adult size, while obtaining substantial improvement in sexual precocity.
Descrição
Palavras-chave
average daily gain, days to gain 160 kg from birth to weaning, Genetic correlation, Heritability, Rank correlation, scrotal circumference corrected to age and live weight, Correlação genética, correlação de rank, dias para ganhar 160 kg, Ganho médio diário, Herdabilidade, perímetro escrotal corrigido para idade e peso
Como citar
Revista Brasileira de Zootecnia. Sociedade Brasileira de Zootecnia, v. 30, n. 1, p. 93-100, 2001.