Epidemiological study of clinical mastitis in dairy cattle.

The incidence rate of clinical mastitis in primiparous Swedish Friesian cows was 15%. The risk of mastitis was greater for calving in July and August and increased with age at calving. Calving disorders and ketosis increased the risk of mastitis 1.8 and 2 fold, while tramped teats and udder injuries increased it 6 and 3 fold, respectively. Herds accounted for 13% of the variation in incidence of mastitis and the risk of mastitis was 1.4 and 1.25 fold greater in high and average producing herds relative to low producing herds. High production predisposed cows for mastitis. Cows with clinical mastitis produced 260 kg less milk and were 2.8 fold more likely to be culled.