The experiment examined the effect of supplementing a roughage diet with lupin grain on the capacity of testicular tissue to produce spermatozoa. Changes in testicle size were estimated by comparative palpation. At the end of the experiment the rams were castrated and the morphology of the testes and their capacity to produce sperm were studied. At the highest level of feed intake, liveweight increased by 32% and testicle volume by 67% during the feeding period of 9 weeks. Rams on a diet that reduced testicle size produced 18 x l06 sperm/g testis per day, and those on a diet that increased testicle size produced 26 x l06 sperm/g testis per day. Those rams whose testes were increasing in size at castration had significantly larger seminiferous tubules, which occupied a significantly greater proportion of the testicle volume, than rams fed on diets that reduced the size of their testes. The variation in rates of sperm production, together with the large differences in testicle weight, resulted in wide differences in total sperm production among rams fed on different diets.

Groups of 50 ewes were injected with serum from pregnant mares on 5 occasions, 3 months apart, and ovulation rate was estimated at laparoscopy. In Exp. 1, new ewes were used at each time and 3 dose rates (identical to 400, 630 and 1000 i.u. PMSG) were studied. In Exp. 2, the same ewes were used throughout and only 1 dose was given (1000 i.u.). In both experiments the response in ovulation rate of ewes varied significantly throughout the year, with the lowest response in spring (September) and the highest in autumn (March). The ewes in Exp. 2 were as responsive at the end as at the beginning of the experiment, indicating that the response was independent of the number of doses given. The results suggest that changes in the sensitivity of ovaries to gonadotrophin may be a factor controlling seasonal ovarian activity in sheep.

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Merino ewes were immunized against bovine serum albumin (BSA), or oestrone or androstenedione, conjugated to BSA. Immunization against oestrone and androstenedione elevated the mean number of ovulations per ewe ovulating (ovulation rate) from 1.2 to 1.5 and 2.3, respectively. The higher ovulation rate was not reflected in more lambs born per ewe lambing (1.12-1 .I 6 for all groups). The frequency of ovulation and oestrus was depressed in ewes immune to oestrone, and there was a high frequency of abnormalities in the reproductive tract. These effects of immunization were not as frequent in ewes immune to androstenedione. There was no relation between titre and any measure of reproductive performance. The use of immunization against ovarian steroids to improve the reproductive efficiency of commercial flocks is not justified without further investigation.