Reproductive issues arising from different management systems in the dairy industry

The objective of this review is to address the reproductive issues arising from different dairy management systems by describing divergent systems and comparing their reproductive outcomes. The increasing global demand for dairy products has led to the majority of the world's milk being produced in intensive management systems. This intensification has occurred in both zero-grazed (ZG) and in pasture-based (PB) systems, and it has contributed directly to the current decline in dairy cow fertility globally. Given the heterogeneous nature of both ZG and PB systems, comparisons between them in dairy cow reproductive performance need to be treated with caution. In general, cows in ZG systems have higher milk production and better energy balance but more of some animal health problems, lower ovarian activity post-partum, reduced oestrous expression, reduced conception success, and higher culling and mortality rates, than cows in PB systems. Key environmental descriptors affecting reproductive performance within management systems include the type and duration of housing and the pre- and post-partum diet composition. Genetic by environment (GxE) interactions for dairy cow fertility have been detected for some, but not for other, management systems. Given the concerns of some consumers within the EU about the health, fertility and welfare of dairy cows in modern dairy herd management systems, there is a need to address these concerns with large-scale experimental and epidemiological studies.