Techniques for the improvement of fertility for prolificacy of anoestrous ewes in Spain

Studies based on progesterone measurement by radioimmunoassay showed that ovarian activity resumed within 30 days when parturition occurred between June and November. Lambing from December onwards was followed by extended periods of ovarian inactivity. Lactation depressed the response to the ram effect. Pregnancy rates at first service were higher in dry ewes than in recently weaned or lactating ewes when prostaglandin (PG) was given 12 days after ram introduction. Experiments aimed at improving the ovulation response to the ram effect concluded that 14 or 16 days is a satisfactory interval from ram introduction to prostaglandin treatment, but the numbers of ewes lambing to first service can be maximized if progesterone pretreatment is given on the day of ram introduction. Attempts to increase ovulation rate, using a single injection of follicle stimulating hormone (FSH) in a slow release vehicle, showed that this method is effective when FSH is given on the day of PG treatment (day 12-14 after oestrus). (author). 4 refs, 3 tabs