Idade ao primeiro parto e intervalo entre partos de vacas HPB e mestiças HPB: Gir

Ages at first calving of 52 Holstein-Friesian (HPB) cows, 69 1/2 HPB: 1/2 Gir (F1) and 66 3/4 HPB: 1/4 Gir (B1) were compared. The animals of all three groups were maintained together in the same herd. Artificial insemination with fresh semen was mainly used, and also natural mating, with HPB bulls for HPB and F1 cows, and F1 bulls for B1 cows. The model for age at first calving included the effects (fixed) of year-season of birth of cow genetic group and the interaction of both effects. Only genetic group effects were significant (P<0.05). The model for calving interval induded the effect of year and season of calving, genetic group, two and three factor interactions of these effects, and linear and quadratic regression on parity. The season x genetic group interaction was significant (P = 0.05). The relation between interval (E) and parity (N) was described by the equation E = 576.21-41.23 N + 4.83 N2, indicating that the minimum interval was attained at the 4th calving.Foram comparadas as idades ao primeiro parto de 52 vacas "Holandês Preto-e-Branco" (HPB), 69 vacas 1/2 HPB: 1/2 Giz (F1) e 66 vacas 3/4 HPB: 1/4 Gir (B1). Os animais dos três grupos eram mantidos no mesmo rebanho. Foram utilizadas principalmente a inseminação artificial com sêmen fresco refrigerado, e a monta controlada com touros HPB para as fêmeas HPB e F1, e touros F1 para as fêmeas B1. O modelo para a idade ao primeiro parto inclui os efeitos (fixos) de ano-época de nascimento da vaca, grau de sangue e a interação destes dois efeitos. Apenas o grau de sangue teve efeitos significativos (P