EFFECTS OF PROSTAGLANDIN F2α ON THE ESTROUS CYCLE AND HORMONE LEVELS IN THE GILT

Abstract

Two experiments were conducted using cycling crossbred gilts 7–9 mo of age. Blood samples were taken daily at 1000 h from day 0 (first day of estrus) to the day of PGF_2α injection; at 1 h and 2 h post treatment, and subsequently every 6 h for 96 h; then daily until the next estrus. In experiment I, 20 mg PGF_2α was injected intramuscularly (i.m.) to three gilts on day 9 (t₁) and to three gilts on day 9 and again on day 10 (t₂). In experiment II, three gilts were injected i.m. with 20 mg PGF_2α on day 12. In both experiments, control blood samples were collected from three of the gilts for one estrous cycle prior to the treatment cycle. Serum progesterone (P) dropped significantly (P <.01) in t₁ from a pre-injection mean (±SE) of 8.9 ± 0.7 ng/ml to 4.8 ± 0.8 ng/ml 8 h after injection. In t₂, P decreased significantly (P <.05) on day 9 from a mean prior to injection of 11.2 ± 2.3 ng/ml to 7.5 ± 1.8 ng/ml by 8 h post injection. Similarly, following PGF_2α on day 10, P levels dropped sharply (P <.05) from a mean of 8.3 ± 0.8 ng/ml prior to injection to 3.8 ± 0.4 ng/ml 8 h later. These decreases were not seen in controls. In all cases, except one, P recovered to normal levels by 96 h and followed a pattern similar to the controls. In experiment II, serum P declined (P <.05) from a pre-injection mean of 12.8 ± 0.9 ng/ml to 7.9 ± 0.7 ng/ml by 2 h after treatment and continued to fall. In contrast, P concentrations on day 12 of the control cycle remained relatively constant. Mean estrogen (E) levels increased slightly within the first hour post injection in both experiments, but were significantly elevated (P <.01) above the pre-injection mean only in t₂ gilts on day 9. Subsequently, E patterns were similar to those of the control cycles. No consistent changes were observed in mean LH concentrations following treatment. Cycle length was unaffected by PGF_2α treatment on day 9, or on days 9 and 10. When PGF_2α was injected on day 12, estrus occurred an average of 1.7 days earlier than in the control cycle (P <.05). Side effects noted within 5–10 mins after injection in both experiments included increased respiratory rate, defecation, shivering and general signs of discomfort.