Cow milk yield and composition before development of Escherichia coli mastitis.
High milk yield, low milk fat and low milk protein were considered as possible predisposing factors to bovine Escherichia coli mastitis. Morning and afternoon milk yields were recorded in 46 Friesian cows later developing E coli mastitis and compared with 92 uninfected controls. Animals developing E coli mastitis gave a significantly higher milk yield than controls. The overall morning: afternoon ratio was (mean +/- se) 1.66 +/- 0.41, with no difference in ratio for the two groups. Further studies on 85 animals later developing E coli mastitis, and 192 controls, in four Friesian herds did not reveal differences in milk fat content (except as related to yield), milk protein or in the interrelationship of days of lactation, milk protein or in the interrelationship of days of lactation, milk fat and milk protein in the two groups. Again there was a correlation between high milk yield and a tendency to develop E coli mastitis but this may have been an age effect in both investigations. No correlation between milk yield and mastitis severity was detected. High yielders which succumbed to E coli mastitis in three herds were producing less milk than mastitis-free controls in the fourth herd which suggests that the correlation is not with yield per se.