Onset of luteolytic action of exogenous prostaglandinF-2α during estrous cycle in goats

- In goats, the luteolysis began at day 3 of estrous cycle (estrus = day 0).
- One single parenteral administration of 5 mg of PGF-2α was effective to induce luteolysis.
- The estrus induced was fertile.

The objectives of these two experiments were to determine the day of onset of luteolysis after exogenous PGF-2α administration during the estrous cycle and the fertility of this synchronized estrus in goats. In the first experiment, during the breeding season, 48 Nubian does were estrous synchronized, using intravaginal sponges impregnated with a progestin, and estrus was detected by vasectomized bucks. The does were divided at random into three groups of 16 does each to be treated at days 2, 3, and 4 of the estrous cycle (estrus = day 0). Then, at each day of injection, the does were again randomly divided to receive a single dose of natural prostaglandin F-2α im (PGF-2α; 5 mg/doe; treatment [TRE] group) or sterile saline solution (control [CON] group; 1 mL/doe). Finally, the following groups were originated: TRE-2, CON-2, TRE-3, CON-3, TRE-4, and CON-4. The overall estrus response after treatment with PGF-2α (TRE group, 70.8%) was higher than saline (CON group, 12.5%, P ≤ 0.001). Estrus response for TRE-2, CON-2, TRE-3, CON-3, TRE-4, and CON-4 was 25% (2 of 8), 12.5% (1 of 8), 87.5% (7 of 8), 12.5% (1 of 8), 100% (8 of 8), and 0% (0 of 8) for the same groups, respectively. Estrus response was different between day 2 and days 3 and 4 (P ≤ 0.04) and not between day 3 and day 4 (P ≥ 0.05). In the second experiment, 15 multiparous Boer does were estrous synchronized with control internal drug release (CIDR, 300 mg progesterone = P4) and PGF-2α and randomly divided to receive one single dose of PGF-2α im at days 2, 3 or 4, after synchronized estrus (n = 5 at each day). The does were detected twice a day for estrus, and blood was collected daily for P4 determination for 11 days after the synchronized estrus. Each doe in estrus was bred by hand mating to a proven male. All the does with a functional corpus/corpora luteum/lutea (CL; ≥1.0 ng/mL of P4) responded to PGF-2α with a drop in P4 levels that either lasted only 24 h for the does that did not show estrus (0.27 ± 0.10 ng/mL; n = 4) or persisted longer in all the does that showed estrus (0.22 ± 0.18 ng/mL; n = 10; P = 0.47). Estrus response for days 2, 3, and 4 was 20% (1 of 5), 80% (4 of 5), and 100% (5 of 5), respectively (P = 0.05). The conception rate was 100%, 100%, and 80% for the same days of administration, respectively (P = 0.64). It was concluded that luteolytic action of PGF-2α begins at day 3 of the estrous cycle by inducing an ovulatory and fertile estrus in goats.