Rates of diagnosis of six diseases of Holstein cows during 15-day and 21-day intervals.

The lactations of 3,172 Holstein dairy cows were divided into intervals of 15 and 21 days. The numbers of new diagnosis of metritis, cystic ovary, miscellaneous reproductive disorders, mastitis, left displaced abomasum, and milk fever in each interval were counted. The numbers of cows at risk in each interval were also counted. A cow was at risk if she was still milking, in the herd, and a diagnosis had not already been made for that condition in that lactation. A cow was also only at risk of a reproductive diagnosis if she was not pregnant. For each interval, the incidence rate of new diagnosis was calculated by dividing the number of new diagnoses by the number of cows at risk.