Abstract
To reduce the intervals from Parturition to conception in normal multiparous mares and to promote the fertility in mares with reproductive failures, 13 mares, a total of 17 cases, were intramuscularly injected with prostaglandin F2α (PG) in the luteal phase. Ten mares came into estrue after the first injection of 5 mg of PG, whereas 3 mares required two or three PG treatments to induce estrus. Estrus was induced 5-8 days after PG treatment in 10 out of 14 cases that showed signs of estrus. The duration of estrus was 3.9 days on the average and 11 out of 17 cases ovulated 8-12 days after PG treatment. The number of matings was 1-5 times during the induced estrus and 11 mares conceived. A “star-like layering of the folds” in the uterine cavity appeared 2-6 days after PG treatment, and then disappeared 1-2 days before ovulation on ultrasonic monitoring. The plasma levels of progesterone (P) rapidly decreased following PG treatment, whereas the plasma levels of inhibin (INH) and estradiol-17β (E2) increased after PG treatment. The plasma concentrations of LH gradually increased following PG treatment and typical prolonged LH surges were observed during the periovulatory period. In contrast, the plasma concentrations of FSH decreased after PG treatment, followed by an increase after ovulation. There was an inverse relationship between the plasma concentrations of FSH and INH. The results of the present study clearly demonstrated that treatment with PG is a useful method for reducing the intervals from parturition to conception in multiparous mares, and for improving reproductive efficiency in mares with reproductive failure.
