Managing fertility in the New Zealand dairy herd

Effective mating management remains crucially important to pastoral milk production systems in New Zealand (spring calving or autumn calving). The incidence of most diseases has decreased since the 1940s, but infertility, especially the ‘anoestrous problem’, has increased despite increased use of hormonal treatments and in association with genetic selection for increased yields of milk. The regular need to treat a high proportion of cows with hormones because they are not cycling at the start of mating should be seen as a sign of mismanagement in the system (genetics, health or feeding). ‘Good herd management’ should be used to achieve good fertility with minimal use of hormone treatments; this will include: good prevention and control of all diseases; all heifers must reach target live weights and puberty at 12 months; all cows must be at BCS 5 at calving, and be fed generously in early lactation; excellent heat detection must be maintained for the entire AI mating period; infertile cows must be culled, and fertility included in the Breeding Worth. These aspects of ‘good management’ must be seen as essential factors in the maintenance of good herd welfare, and in the sustainable production of the high quality, clean and green dairy products required by the world markets. A number of commercial herds are showing that good fertility and good productivity can be achieved with minimum use of hormone treatments, with presentday cows. However, for some strains of cows, good feeding management may be impossible on a diet of grazed pasture.