Relationships between milk yield, post-partum body weight and reproductive performance in Friesian x Bunaji cattle

The data consisted of 369 lactation records for calvings over a sixteen-year period (1972-1987) and included only cows that had normal milk records. The data were analysed using a linear model containing the fixed effects of parity, year of calving and season of calving. The least squares means ± S.E. were 1,273±58.4 kg for milk yield, and for postpartum body weight (kg) at 2, 3 and 4 months after calving were 343.40±3.96, 346.10±4.10 and 352.54±4.26 kg, respectively. With the exception of season of calving, the effects of parity and year of calving were significant (P<0.01) on the performance of the animals. Thus, the mean milk yields 1162, 1351 and 1350, were similar for pre-, peak- and post-rainy seasons, respectively. On the other hand, as parity increased from 1 to 3, milk yield also increased, but thereafter, there was a gradual decline in milk yield. Similarly, postpartum body weight also increased with parity. However, no consistent pattern for year effect was observed, which probably was a reflection of the variation in climatic conditions, or forage quality and/or availability. The phenotypic correlations between milk yield and post-partum body weights were negative and small (ranging from 0.01 to -0.08). However, high milk production in cows was associated with longer calving interval. The implications from the phenotypic correlations are suggestive of one or two possibilities. Firstly, selection for increased body weight may actually result in decreased milk yield. Also, a substantial genetic antagonism may exist between milk yield and fertility in the crossbred cows. Therefore, it is important that selection to improve milk production should take into consideration the reproductive performance of the cows.