The incidence rate of clinical mastitis in primiparous Swedish Friesia
n cows was 15%. The risk of mastitis was greater for calving in July a
nd August and increased with age at calving. Calving disorders and ket
osis increased the risk of mastitis 1.8 and 2 fold, while tramped teat
s and udder injuries increased it 6 and 3 fold, respectively. Herds ac
counted 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 produci
ng herds relative to low producing herds. High production predisposed
cows for mastitis. Cows with clinical mastitis produced 260 kg less mi
lk and were 2.8 fold more likely to be culled.