Quarter‐milking‐, quarter‐, udder‐ and lactation‐level risk factors and indicators for clinical mastitis during lactation in pasture‐fed dairy cows managed in an automatic milking system

Abstract

To identify risk factors and indicators at quarter-milking and other levels for clinical mastitis during lactation in pasture-fed cows managed in an automatic milking system. A retrospective nested case-control study using data collected over a 31-month period. A total of 803,948 quarter-milkings from 249 cows were available for analysis, of which 245 were selected as clinical mastitis quarter-milking cases and 2450 unaffected quarter-milkings were selected as controls. Most of the diagnoses of clinical mastitis had been made after clinical assessments of quarters following automated alerts by the milking system. Potential risk factors and indicators were assessed using univariable and multivariable multilevel logistic models. Quarters that are milked infrequently and have low yield, fast peak milk flow rates, blood in the milk and/or elevated milk conductivity are at increased risk of clinical mastitis. Quarters were also at increased risk between days 10 and 29 of lactation, and during higher parity lactations. Milk fat and protein concentrations and the fat:protein ratio were not significantly associated with the development of clinical mastitis. Neither quarter position (fore or rear) nor side (left or right) was associated with clinical mastitis occurrence. Quarters that had been clinically affected more than 30 days previous in the current lactation were not at increased risk of redeveloping clinical mastitis. Under the study conditions, the risk of clinical mastitis increased for quarter-milkings in quarters that were milked less frequently in the previous 7 days, were low-yielding, had fast peak milk flow rates and had more milkings in which blood was detected in milk and/or the milk conductivity was elevated. Risk was also increased in days 10-29 of lactation and in higher parity lactations.