Characterising Lactation Curves in Heifers of Different Breeds First Calved in Moderate or Low Condition

Milk yields were measured every 6 weeks from 21220 days after calving in either moderate or low conditioned groups of Angus, Angus x Friesian or Simford first-calf heifers for 3 successive years. Day of peak yield, peak yield and total 220 day yield were calculated by fitting 3 published equations to data on each of the breed x year x calving condition combinations. All equations ranked breed and calving condition combinations similarly for 220 day milk yield, but peak yield and day of peak yield were more variable. The Jenkins equation consistently accounted for more variation in milk yield data (58%) compared with the Wood and Wood-weighted milk curves. Calf weight at 200 days and estimated 220 day milk yield (Jenkins) were highly correlated (r = 0.59, P c 0.001).