The effect of body size and body condition on the ovulation rate of ewes

SUMMARY Body size was estimated for 255 Greyface ewes using five linear body dimensions. On the basis of this calculated measure combined with a subjective measure of body size 50 small and 50 large ewes were selected for use in the experiment. Precise ovulation data were obtained by endoscopy and this technique allowed the ewes to be mated subsequently. Body size did not affect the mean ovulation rate of the ewes although, at the same level of body condition, the large ewes were 25% heavier than the small ewes. The ovulation rates and the numbers of lambs born were influenced by changes in live weight and body condition. For these reasons live weight per se was not a good indicator of ovulation rate as ewe live weight was a combination of both body size and body condition. At the same live weight small ewes in improving body condition had a significantly higher ovulation rate than large ewes in reducing body condition. The onset of the breeding season of the ewes was not affected by their body size. The mean date of onset of oestrous activity for both large and small ewes was 17 October 1972 at a latitude 55° 52′ N.