The primary production unit on a New Zealand dairy farm is the milking herd, which consists of mixed-age cows that have given birth to at least one calf and have ages typically ranging from 2 to 10 years. The maximum total size of the milking herd often constrained by feed supply, farm infrastructure, and management preferences. The milking herd is supported by a pipeline of young stock to replace cows as they leave the herd through death or culling.
In New Zealand dairy systems, a mob refers to a defined group of cattle managed together as a unit for grazing, feeding, movement, or husbandry. A mob may include the whole milking herd or a subset of animals grouped by age, stage of lactation, production level, or management needs, such as first-calvers, high-producing cows, or dry cows. Mobs are used to simplify daily management, control grazing rotations, and match feed allocation and care to the needs of different classes of stock.
Annual replacement rates in New Zealand dairy herds typically range from 15–25% with a current industry average of around 22%, equivalent to an average herd life for a cow of about 4.5 lactations cycles. Economic modelling suggests that an optimal replacement rate closer to 18% can maximise profitability and genetic gain by balancing rearing costs with improvements in herd performance.
The process of selecting replacements begins immediately after birth. On average per herd, around 28% of calves are retained as dairy replacements, 12% are reared on-farm for beef, 15% are sold for beef rearing, 35% are sold for processing as bobby calves, 5% are euthanised, and 4% are stillborn or die shortly after birth. Bobby calves are predominantly male calves along with some female heifer calves, typically those produced from mating to beef sires, that are slaughtered shortly after being born rather than being raised for dairy beef production. Under New Zealand regulations, calves must be at least four days old before transport off-farm and cannot be transported for more than 12 hours if under 14 days of age.
The heifer calves kept as replacements are typically housed in calf sheds for their first week of life, then moved onto pasture and fed a combination of milk, calf pellets, and/or hay until weaning at around 8–12 weeks of age, depending on the system.
Edwards, J.P., Cuthbert, S., Pinxterhuis, J.B., & McDermott, A. (2021). The fate of calves born on New Zealand dairy farms and dairy farmer attitudes towards producing dairy-beef calves. New Zealand Journal of Animal Science and Production, 81, 179–185.
From weaning, young stock become R1 heifers (rising 1-year-old heifers) from around 3 to 12 months of age, when growth is focused on skeletal development to ensure they reach puberty by 8 to 14 months of age. From around 12 to 24 months, they become R2 heifers (rising 2-year-old heifers), during which they are mated so they calve for the first time at approximately two years of age and join the milking herd. A small proportion of animals may calve later as R3 heifers at around three years of age, usually due to growth delays or management decisions. Some farmers elect to raise all of their replacement heifers on farm, while others will use contract grazing, hiring someone else to rear their heifers off-site. If there are insufficient pregnant replacements heifers to maintain herd size, farmers may also choose to purchase in replacement heifers or mixed-age cows from external sources.
The milking herd then cycles through annual lactation, with cows dried off in late autumn or early winter to allow recovery before the next calving season. Alongside replacement, herd size is managed through culling, which is the planned removal of cows due to factors such as infertility, low production, age, mastitis, lameness, injury, and other disease or welfare concerns. Planned culling most often occurs around the time of dry-off to avoid the costs of feeding additional animals over winter, although some are removed during the season if acute issues arise or if animals are dried off early because of poor feed availability. Cull cows that are fit for transport are typically sent to an abattoir or slaughterhouse (also called “the works” or “meatworks”) for meat processing.
A springer is a cow in late pregnancy that is close to calving, usually within the final few days to one to two weeks before birth. Springers are identified by signs such as udder filling, slackening around the tail head, and behavioural changes, and are a key focus of management during the spring calving period. A springer mob is a group of springer cows managed together and kept separate from the main milking herd so they can be closely monitored in the lead-up to calving. In seasonal, pasture-based systems, springer mobs are typically grazed in paddocks close to the shed or housed in close-up pens or calving areas, allowing frequent observation (usually every 4 to 6 hours), timely assistance at calving if needed, and easy movement of cows into the milking herd once they have calved.
Advancing Animal Care through Shared Learning