TEMPORAL PATTERNS OF LOST MILK-PRODUCTION FOLLOWING CLINICAL MASTITIS IN A LARGE MICHIGAN HOLSTEIN HERD

Cows with three hundred and sixteen cases of clinical mastitis were sampled by microbiologic culture during a 6-mo period on a 1700-cow Michigan Holstein dairy farm. Daily milk weights were obtained on all cows before clinical onset and for 60 d after onset. Predicted postmastitis production, projected on the basis of premastitis production and the lactation curves of contemporary nonmastitic herdmates, was compared with actual daily milk production during the 60 d following clinical onset. Cows experiencing clinical mastitis produced approximately 341 kg less salable milk during the 60 d after clinical onset compared with projected production. This milk loss included both decreased production and milk withheld from market following antibiotic treatment. Pluriparous cows lost 2.06 times as much milk as first lactation cows, and cows with mastitis occurring before 150 d in lactation lost 1.40 times as much milk when compared with other cows. Cows with mastitis occurring in the winter showed a milk loss 1.37 times greater than cows with mastitis in summer. The identity of the mastitis agent isolated from the clinical case was not strongly associated with the drop in milk production in the 60 d following clinical onset.