Factors Affecting the Incidence of Cystic Ovaries in a Herd of Holstein Cows

Summary Factors affecting the incidence of cystic ovaries have been examined in a herd of Holstein cattle. The records covered 341 cows and 1,280 cow-service periods over a 10-yr. period. Cystic ovaries occurred in 18.8 per cent of the cows and 7 per cent of the service periods. The proportion of the cows becoming cystic for the first time averaged 0.058 per service period and no evidence was obtained for significant variation in this rate between service periods. Heritability of the occurrence of cystic ovaries sometime during life was estimated for this herd as 0.43. No evidence was obtained for an association between inherent level of butterfat production or test and the occurrence of cystic ovaries. Cows when not milked (mainly in the heifer service period) showed an incidence of cystic ovaries of 3.4 per cent; those in the milking herd, 6.8 per cent; those started on test and then removed to the milking herd, 8.5 per cent; and those on official test, 10.6 percent.