The effect of dietary protein on reproduction in the mare. III. Ovarian and uterine changes during the anovulatory, transitional and ovulatory periods in the non-pregnant mare.

In the main experiment the total daily protein intake and quality (essential amino-acids) was varied in 4 groups of mares. The incidence of oestrus in mares during the transitional period was unaffected by protein nutrition. Ovarian activity, as evaluated by follicular development and size of the ovaries, was affected. Mares that received low-quality protein (Groups 1 and 2) had a higher number of smaller follicles (< 10 mm) that developed during the transitional period compared to mares on a high-quality protein intake (Groups 3 and 4). The mares that received the high quality protein ovulated 2-3 weeks earlier in the breeding season in a synchronised period of 4-5 weeks compared to a period of 6-8 weeks in Groups 1 and 2. The duration of the subsequent oestrous cycles was not affected. There was no difference in the diameter of the largest follicle of mares between groups on the day before ovulation. In a separate experiment, 5 maiden Anglo-Arab mares, 4-5 years of age, were slaughtered at different stages during the anovulatory, transitional and ovulatory periods of the breeding cycle. The morphology of the ovaries and uteri of these mares was described and photographed for use as guidelines when comparing ovarian changes and follicular activity of mares.