Age and weight at first calving and subsequent performance in Dutch dairy cattle from rearing farms

Relationships between age at first calving and first lactation milk yield, and lifetime productivity and longevity in dairy cows

Lifetime records of 442 Holstein cows on one farm in North Queensland, Australia, were analysed to evaluate the effects of age at first calving (AFC) and first lactation milk yield on parities per lifetime, longevity, milk yield in subsequent lactations, lifetime milk production and the longevity index (LI), that is the proportion of a cow's life spent in active milk production. The mean daily yield in the first lactation was a reliable indicator of milk yield in subsequent lactations, estimated lifetime production, longevity and LI. The afc had no effect on lifetime days in milk. Neither the AFC nor the milk yield in the first lactation significantly affected the number of parities per lifetime. For the majority of cows, which produced less than 30 l/day in the first lactation, there was a significant positive relationship between longevity and AFC. However, none of the cows that produced more than 30 l/day in the first lactation survived for more than two lactations. The optimal AFC was thus two to two-and-a-half years, as these cows had the highest first lactation yield, estimated lifetime production and LI. The optimal mean daily yield in the first lactation was 20 to 30 l/day, as these cows lived longer and had a higher LI and lifetime production.

Production of dairy replacement stock in relation to level of exposure to gastrointestinal nematode infection in the first grazing season: second-year calves and heifers

In two experiments, groups of calves which had been exposed to different levels and patterns of infection with Ostertagia and Cooperia spp. in a simulated first grazing season (FGS), were followed throughout a natural second grazing season (SGS). Milk yields in the subsequent first lactation period were also recorded. The results suggest that although there had been differences in immune status among groups, which had been infected in the FGS, prior to the SGS, weight gain among these groups was not significantly different during the SGS. Apparently, resistance to the pathogenic effects of reinfection had developed more strongly and at lower levels of exposure to infection than resistance against establishment of larvae as shown after an experimental challenge. The groups of calves not infected during the FGS did gain less than all other groups during the SGS. Further, infection-induced differences in weight gain among the infected groups in the FGS appeared to be permanent, at least up to the end of the SGS. Finally, first lactation yield was positively correlated with body weight at calving. On average, approximately 10 kg less milk was produced for each kg of lower body weight at calving. With respect to the implications for preventive control strategies in the FGS, it is suggested that parasite control should not be applied beyond a level at which weight gain reduction is prevented.