Comparative performance of six Holstein-Friesian × Guzera grades in Brazil 1. Gestation length and birth weight

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Abstract
Gestation length and birth weight of 939 calves born at Santa Monica Experimental Station, Valenc, a, State of Rio de Janeiro, were studied. The calves were of six red and white Holstein-Friesian (HF) × Guzera (G) grades: 1/4, 1/2, 5/8, 3/4, 7/8 and ≥ 31/32.As the grade × sex interaction for birth weight was significant, data for each sex were analysed separately. A model, including the effects of grade, year-season of birth, grade × year season interaction and age of dam as a covariate, resulted in the following least-square means for the six grades in the above order (± s.e.): gestation length for cows carrying male calves, 290·0 (± 0·9), 281·2 (± 0·9), 285·3 (± 0·8), 278·8 (± 0·9), 280·5 (± 0·9) and 279·3 (± 0·9) days; gestation length for female calves, 287·5 (± 0·9), 280·1 (± 1·0), 285·3 (± 0·9), 274·5 (± 1·1), 279·2 (± 0·9) and 276·4 (± 1·0) days; birth weight for males, 34·6 (± 0·7), 28·6 (± 0·8), 34·2 (± 0·7), 32·4 (± 0·7), 35·0 (± 0·7) and 34·7 (± 0·7) kg; birth weight for females, 29·9 (± 0·6), 29·5 (± 0·7), 33·4 (± 0·6), 31·9 (± 0·7), 33·6 (± 0·6) and 32·6 (± 0·6) kg.Direct (g1) and maternal (gM) breed additive effects (HF - G), and direct (h1) and maternal heterosis (hM) were estimated. The estimates of g7, gM, h1 and hM were respectively, for gestation length for male calves: -21·5 (± 1·9), 10·6 (± 2·1), 1·5 (± 1·8) and -1·6 (± 11) days; for gestation length, for female calves: -21·9 (± 2·1), 14·6 (± 2·5), 5·7 (± 2·1) and -1·5 (± 1·2) days; for birth weight of male calves: -3·5 (± 1·5), 7·1 (± 1·8), -0·6 (± 1·5) and 1·0 (± 0·9) kg; and for birth weight of female calves: 4·7 (± 1·4), 4·1 (± 1·6), 2·8 (± 1·3) and 2·0 (± 0·8) kg. The difference in birth weight between males and females was 4·7 (± 0·9) for G-sired calves and 0·8 (± 0·4) for HF-sired calves.