PATTERNS OF FOLLICULAR DEVELOPMENT DURING PERIODS OF ANOVULATION IN PASTURE-FED DAIRY-COWS AFTER CALVING

The ovaries of 17 Friesian cows aged two to seven years were examined daily by transrectal ultrasound from one week after calving. The posit ion and size of all follicles more than 2 mm in diameter were recorded . A large (more than 9 mm in diameter) follicle was present on at leas t one ovary by six to 17 days after calving, and in two of the cows it ovulated; the remaining cows had from two to nine large follicles bef ore they ovulated. The mean (SEM) interval from calving to the first o vulation was 43.4 (5.3) (range 13 to 93) days, after 4.2 (0.6) waves o f follicles.