Machine-induced teat tissue reactions and infection risk in a dairy herd free from contagious mastitis pathogens.

Machine-induced changes in teat thickness were measured in a randomly selected group of 22 cows from a commercial dairy herd consisting of 110 cows during an experiment lasting 1 year. Half the cows used were free from mastitis whereas the remainder had at least one quarter infected by environmental pathogens. Teats were classified according to a threshold change in teat end thickness of 5%. The relationships between quarter infection or teat duct colonization and teat end thickness changes induced by machine milking were investigated. Teats with greater than 5% change in thickness had significantly increased teat duct colonization and a slight, non-significant, increase in quarter infection. We conclude that machine-induced changes in teat end thickness are predisposing factors for teat duct colonization by environmental pathogens. This may provide an increased new infection risk, especially when hygiene is poor.