Ciência Rural (Sep 1999)
Heterozigose individual e materna sobre o ganho de peso do nascimento ao desmame de terneiros Pampiano-Braford Individual and maternal heterozigosis on preweaning weight gain of Pampiano-Braford calves
Abstract
Foram analisados dados de ganho de peso do nascimento ao desmame (GNDa) de animais Pampiano-Braford (cruzamento de Nelore X Hereford) criados no Rio Grande do Sul com a finalidade de verificar a influência da heterose individual (HI) e materna (HM) sobre o GNDa e quantificá-la. Os dados foram pré-ajustados para idade da vaca (IV), data juliana de nascimento (DJN) e idade do terneiro ao desmame (IT). Entretanto, análises exploratórias sugeriram que as pré-correções para IV, DJN e IT não estão ajustando corretamente os dados (PData on preweanning gain (GNDa) of Pampiano-Braford animals raised in Rio Grande do sul were analyzed to verify the influence of individual (HI) and maternal (HM) heterosis in GNDa, and to quantify it. Data were adjusted for dam age (IV), julian birth date (DJN)and calf age at weaning,(IT). However, exploratory analysis have suggested that the adjustment factors for IV, DJN, and IT are not doing this adjustment correctly (P<0.01). Because of the structure and connectedness of the major data set, the analysis was done in two different ways. In the first phase, HI and HM were estimated simultaneously, in file 2, compose of 4186 animals, and the values obtained were 31.91 and 33.53kg, respectively. In the second phase, HI was estimated in a subset of file 2 (subset 1) compose of 1507 animals with maternal heterozigosis 0.0000; HM was estimated in subset 2 of file 2 with 2777 animals with individual heterozigozis 0.5000. The values found were 13.79 and 34.08kg, respectively. All the values found for heterosis on GNDa were significant (P <0.01), and the relation between heterosis and heterozigosis for this characteristic was linear (P< 0.01). It was show that the Hereford animals, in this study, had greater genetic additive values than crossbreeds, but this difference was not sufficient to supress the effects of heterosis on GNDa. In comparison with the values used in GenSys Method, the HI and HM values, obtained in this study produced a change in the ranking of calves at preweaning, but the number of animals chosen in common by the two methods did not differ much. The cows with 1/2 breed composition had the best performance on GNDa, while the calves with maximum heterosis (breed composition 1/2) were excelled by those 3/8, when HM was included in the performance, emphasizing the importance of HM on GNDa.
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