A seven-year-long AgResearch study has revealed some promising results into calf development and herd performance.
AgResearch’s Senior Scientist from the Bioeconomy Science Institute’s Animal Nutrition and Physiology Team, Ajmal Khan takes us through ways to boost milk yield and herd performance.
Getting your heifer calves off to a strong start is one of the most important things you can do to improve your herd's performance in New Zealand’s pasture-based dairy systems.
A seven-year-long study by AgResearch followed 324 Kiwi-cross heifers across two conventional and two organic farms, all using a standardised colostrum management protocol. The goal was to explore how early-life factors, protein in blood serum (TP; a marker for passive/colostrum immunity) and pre-weaning growth, relate to long-term outcomes like milk production, reproduction performance, and herd retention.
The preliminary analysis indicates that colostrum quality is critical for passive immunity and calf health in early life. However, this study found that while colostrum quality and blood TP levels were important for initial immunity, they had minimal impact on udder development, reproduction or milk production later in life.
What did make a difference was how fast calves grew before weaning, known as pre-weaning average daily gain (ADG). In this study, heifers that grew faster (data set range between ADG ~400g and ~900g per day from birth to three months) stayed heavier right through to calving and produced more milk and milk fat over their first four lactations.
The standout finding? For every additional 100g per day in pre-weaning ADG, heifers produced around 279kg more milk per lactation. That’s roughly 23.5kg more milk solids, a significant boost from just a small increase in early growth.
Now imagine the yield advantage if pre-weaning growth increased from 400 to 900 g/day – this could result in an additional 96kg of milk solids per lactation. That’s roughly 15-20% more milk per NZ cow, a major gain in productivity from simply growing calves better early on. That’s a strong return on early investment, which in this study, was carried to the fourth lactation.
Although there was a slight negative association between faster early growth and ultrasound-measured mammary development, this did not reduce milk yield; in fact, the opposite was true. Heifers with lower ADG were also more likely to be culled earlier from the herd, reinforcing that early growth supports both survival and productivity.
So, what could this mean for your farm?
Ensuring calves grow well before weaning by offering enough high-quality milk or milk replacer, good access to high-quality starter feed, and maintaining excellent hygiene can set them up for a more productive life in the milking herd. While managing colostrum intake is still vital for immunity, early weight gain is a stronger predictor of lifetime milk production.
This lifetime study has generated clear evidence that investing in good nutrition and calf care in the first weeks pays back with higher yields and stronger herd performance over time.
This study was funded through the AgResearch Strategic Science Investment Fund.
