Rearing conditions and lifetime milk revenues in Swedish dairy cows

Associations between replacement heifer rearing conditions and lifetime milk revenues were studied throughout the productive life of Swedish dairy cows. Data were collected from 2127 cows, mainly Swedish Reds and Swedish Holsteins, representing all female animals born during 1998 in 110 herds and followed until May 2006. Lifetime net milk revenues were calculated for each cow based on the length of productive life, lifetime milk production, a fixed milk price of 0.3 €/kg ECM, and estimated costs for heifer rearing and cow feed. Median observed productive lifetime to culling, death, selling off or terminated recording was 26.9 mo. Mean lifetime production was 9209 kg ECM/cow-yr, calculated from monthly testday yields. Rearing costs (median 631 €) were estimated using a template developed for Swedish advisory services, including costs related to purchase, feeding, labour, building investment, building maintenance and breeding. Net milk revenues had a median of 1169 €/cow-yr during productive life and were heavily skewed. Diarrhea and respiratory disease before 7 mo of age had occurred in 11 and 11% of the cows, respectively, the majority cases being mild. The mean prepubertal growth rate was 670 g/day. Cow net revenue values were transformed to achieve normality and analysed by a linear mixed model including fixed effects of breed, calf housing system from 3 to 7 mo of age, body condition score at 1st breeding, year of 1st calving, age at 1st calving, cow housing system, mean milk cell count, the interaction between calf housing and breed, the interaction between cow housing and breed, and the random effect of herd. The model predicted net revenues to decrease with age at 1st calving and with body condition score at breeding over 4. Our results show that replacement rearing factors influence net milk revenues of a dairy operation and suggest that current recommendations to breed dairy heifers for calving at 24 mo are economically justified