Inhibition of Heat by Progesterone and Its Effect on Subsequent Fertility in Gilts2

Publisher Website
Google Scholar
Abstract
Ninety-five gilts of mixed breeding were used in three trials to test their response to injections of crystalline progesterone (levels of 25 and 100 mg. daily started on day-10 or -15 of the estrous cycle and continued through day-28) with the objectives being (1) to develop a treatment which would inhibit heat and ovulation and would be followed by a fertile heat, and (2) to observe the effects of incomplete ovulation on fertility. Heat was inhibited by progesterone on both dosages and at both times of onset of injections. However, the fertility of the heats following these injections was nil in those gilts on the 25 mg. dose and low for those on the 100 mg. level with injections begun on day-15. The latter showed the following results: Heat was inhibited in all gilts during treatment. The heat period subsequent to treatment (shown by 34 of 36 gilts) was shortened by an average of 0.3 days. The average number of cysts in the 18, 3-day gilts, observed following treatment, was increased by 6.5 over the controls. Four of these 18 gilts had only cysts. The average number of fertilized ova was decreased by 5.5 ova (reflecting ovulation decrease, ova loss and fertilization failure). Embryonic death was not materially altered by the progesterone treatment. Those control and experimental gilts which had ovulated were divided into cystic and non-cystic subgroups. It was then found that progesterone increased the ovulation rate over all experimentals by 3.2 ova. There was a much greater increase in number of lost ova in the cystic gilts over the non-cystics, both receiving progesterone, than in similarly classed gilts not receiving progesterone. Fertilization failure was significantly increased over all progesterone groups but was not affected by the cystic condition.