Ciência Rural (Dec 2000)
Época de nascimento no crescimento de bezerros aberdeen angus criados no Rio Grande do Sul e suas implicações no melhoramento genético Calving season on growth of angus calves raised in the State of Rio Grande do Sul - Brazil and its implications on genetic improvement
Abstract
Os objetivos deste trabalho foram determinar a existência de interação entre época de nascimento e os efeitos de sexo do bezerro (S), idade da vaca (IV) e idade do bezerro (ID), e estimar o efeito da época de nascimento sobre o crescimento dos bezerros do nascimento ao sobreano. Foram utilizados registros de peso à desmama (PD) de 40.915 animais Aberdeen Angus, criados no Rio Grande do Sul, nascidos na primavera e no outono, entre os anos de 1974 e 1997. Desses, 12.706 tinham pesagem ao nascer e, 22.448, peso ao sobreano (PS). As análises foram realizadas por meio de dois modelos: o primeiro contendo todos os termos de interação, com a finalidade de verificar a possível importância da interação entre os efeitos de IV, S e ID com época de nascimento sobre o PD, e o segundo com os efeitos aninhados dentro de época de nascimento, para comparar o crescimento dos bezerros de outono e primavera. A interação de época de nascimento foi significativa com S (PThe purpose of this study was to determine the existence of interaction between calving season and sex of calf (S), age of dam (AoD) and age of calf (AC) and estimate the effect of calving season on growth of calves from birth to yearling age. Weaning weights (WW) from 40,915 Angus calves raised on 69 ranches located in the State of Rio Grande do Sul, southern Brazil, born in the Spring and Fall from 1974 to 1997, were used. The data set contained 12,706 birth weight and 22,448 yearling weight (YW) records. The analyses were made using two models: the first, including all the interaction terms, was set up to verify the effect of two by two interactions involving calving season and the effects of S, AoD and AC, and the second with those effects nested within calving season, to compare pre- and post-weaning performance of Spring and Fall calves. The interactions of calving season with S (P<0.0001), AoD (P<0.0001) and AC (P<0.05) were significant. Correction factors for age of dam, age and sex of calf, used in genetic improvement programs in southern Brazil, must be estimated within calving season. Adjusted weaning gain and WW of Spring calves were, respectively, 15.6% e 12.9% higher than those from Fall calves. Post-weaning gain was 22.6% higher for Fall calves, making YW 4.2% higher in these animals, compared to those born in the Spring.
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