In spring, pastures grow most rapidly and cows produce the most milk. Cows are mated to produce their calves in mid- to late winter, so that they lactate during the peak season. On seasonal-supply farms, daily milk flows slowly diminish until cows ‘dry off’ in autumn, and they are not milked from May to July. During this time cows may be moved to another farm or feed pad, so pastures can recover or be renovated.
Total milk production from New Zealand’s 4 million cows builds in late spring to 80 million litres a day, and dairy companies must have enough transport and processing equipment to handle the peak in mid-November. Every day the perishable milk has to be converted into cool-stored products like powders and cheeses.
Pregnancy for a cow lasts 282 days (around 9.5 months), so she must be mated or artificially inseminated around early October if she is to calve in mid-July the following year.
Cows are generally left alone to calve, although occasionally a farmer has to assist. Calves are usually taken from their mother after they have taken the first high-colostrum milk. The calves are kept together in a warm, dry shed and fed milk from a tank with artificial teats. Gradually they are introduced to dry feed (cereal-based meal or pellets), and then to grass as their rumen develops.
Bull calves are slaughtered for veal or raised as beef cattle. Heifer calves are reared as dairy or beef herd replacements. Dairy heifers are mated at 15 months of age, to produce their first calf at the age of two. They will then stay in the milking herd for four to five years.
Traditionally, milking was done twice daily, but a number of farmers now milk their cows only once a day. They report a slight reduction in milk production, but say that this is offset by lower labour and operational costs.