Factors Affecting Ovulation and Follicular Cyst Formation in Sows and Gilts Fed 6-Methyl-17-Acetoxyprogesterone

Publisher Website
Google Scholar
Abstract
Five trials involving 193 sows and gilts indicate that 6-methyl-17-acetoxyprogesterone doses of 100 mg. or greater are required to inhibit estrus and ovulation in the gilt. One or more cystic follicles developed in 58% of the females after withdrawal of eight different hormone doses ranging from 50 to 400 mg. per head per day. Cystic follicles developed during treatment when a low dose of 60 mg. was fed and after treatment when the dose was 240 mg. Gilts fed 75 mg. developed fewer cystic follicles after hormone withdrawal if treatment was started during the follicular rather than the luteal phase of the estrous cycle. Sows maintained preovulatory size follicles for at least 8 days after the withdrawal of 200 mg. or more, and gilts maintained pre-ovulatory size follicles for 8 days or more after the withdrawal of 400 mg. Sows also reached other dose response end points at a lower level than gilts. Increasing the duration of hormone feeding from 10 to 20 days resulted in more corpora lutea or follicles>6 mm. in diameter, fewer cystic follicles and more preovulatory size follicles at 8 days after hormone withdrawal. After withdrawal of a 240 mg. dose, Yorkshire sows had developed cystic follicles; whereas Duroc sows had developed preovulatory follicles. Neither frequency of feeding the progestational hormone, the energy content nor the fiber content of the ration affected the probability of ovulation or cystic follicle formation after hormone withdrawal.