Fertility data were collected every four weeks for 10 years from 40 herds of Holstein-Friesian dairy cattle. The data collected during 925 lactations from cows with cystic ovarian disease which were treated with 500 pg gonadorelin were compared with data from a control group of 13,869 normal lactations. The intervals between parturition and first insemination and between parturition and conception were significantly shorter (P<0-001) in the normal cows, but the interval between first insemination and conception was not. The overall conception rate tended to be higher (P<0-10) in the normal cows, but the conception rate after the first insemination was significantly higher (P<0-001) and the number of services per conception was significantly lower (P=0-008) in the normal cows.

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