Lifetime risk and cost of clinical mastitis in dairy cows in relation to heifer rearing conditions in southwest Sweden.

Relationships between heifer rearing conditions and the risk of veterinary-reported clinical mastitis (VRCM) during productive life were studied by generalized linear mixed modeling at the lactation level. Data consisted of 5,693 lactations in 2,126 Swedish Reds, Swedish Holsteins, or dairy cows of other or mixed breeds, representing all female animals born in 110 herds in southwest Sweden in 1998. During a lactation, a cow was defined as affected by VRCM if one or more cases were reported by a veterinarian, starting from 7 d precalving. The applied model of VRCM included effects of breed, parity, diarrhea between 3 and 7 mo of age, increase in body weight from weaning to first breeding, increase in daily concentrate ration before first calving, herd-level median age at first calving, cow housing, and random effects of cow and herd. The VRCM incidence was 14% in a given lactation, or 0.11 cases/cow annually; 31% of the cows had VRCM at least once during their productive life. Ninety percent of the variation in mastitis risk was due to factors at the lactation level such as parity, milk yield, cow diseases, and other disturbances, instead of cow or herd factors. Severe diarrhea between 3 and 7 mo of age was associated with 2.8-fold higher odds of VRCM compared with mild diarrhea during the same period, whereas the VRCM odds of calves with mild diarrhea were half that without diarrhea. The odds of VRCM had a predicted maximum at an estimated prepubertal growth rate of 859 g/d and increased with 10% for every 1-kg increase in concentrate ration during the last 2 mo before first calving. Costs of VRCM were estimated based on assumptions regarding veterinary service, extra labor, culling and herd replacement, discarded milk, and production loss depending on parity and lactation stage when VRCM was diagnosed. The total mean costs of VRCM were estimated to be $735 per lactation with a diagnosis of CM, $103 per lactation across all cows, or $95 per cow annually during lifetime.