Estrous, ovulation and reproductive responses of ewes synchronized with a long interval prostaglandin-based protocol...

The aim was to characterize and assess the reproductive performance of a long interval prostaglandin (PG)-based protocol for timed AI (TAI) at different times. During breeding season three experiments were done involving 622 Merino ewes, 11 rams, and five androgenized wethers per 100 ewes. All ewes were estrus synchronized with two PG injections 15-day apart (PG15): Day -15 and 0 (Hour 0). Estrous distribution respect to Hour 0, estrous response and synchrony after Hour 0, and interval from Hour 0 to estrus detection (PG-estrus) was evaluated (Experiment I; n = 105 ewes). Interval from estrus detection to ovulation (estrus-ovulation) and from Hour 0 to ovulation (PG-ovulation) was determined (Experiment II; n = 12 ewes). Visual-physical score of cervical mucus at TAI, non-return to service to Day 23 (NRR23), fertility, prolificacy, and fecundity to Day 60 in four cervical fresh semen TAI groups was evaluated (Experiment III; n = 505 ewes; 107 nulliparous-398 multiparous). Three groups with single service at 56 (Control), 44 or 68, and one with double service at 44 and 68 ± 1.5 h after Hour 0 (PG15-56, PG15-44, PG15-68, and PG15-44/68 groups, respectively) were tested. Ninety-eight-point one percent of the ewes showed estrus from Hour -48 up to 84 respects to Hour 0. Twenty percent of them showed estrus from Hour -48 up to 0, and 78.1 % from Hour 12 up to 84 (Experiment I). The largest proportion of ewes in estrus was observed between Hour 36 and 60 (80.5 %). PG-estrus interval was 54.1 ± 10 h (means ± SD). Estrus-ovulation interval was 32.4 ± 5.8 h, and PG-ovulation interval was 77.0 ± 16.6 h (Experiment II). Ewe parity did not affect any of the reproductive variables (P > 0.05; Experiment III). There were no significant differences (P > 0.05) between Control and different groups in mucus score (2.18 ± 0.08, 2.02 ± 0.07, 2.14 ± 0.09, 2.25 ± 0.10), NRR23 (76.0, 71.9, 78.6, 79.4 %) or fertility (66.4, 64.1, 66.7, 73.8 %; PG15-56, PG15-44, PG15-68 or PG15-44/68 groups, respectively). Prolificacy in PG15-44 group was lower (1.07 ± 0.03; P < 0.05) than other groups (1.27 ± 0.05, 1.23 ± 0.05, 1.20 ± 0.04), and fecundity than PG15-44/68 group (0.84, 0.69, 0.82, 0.89), without differences among other groups (PG15-56, PG15-44, PG15-68 or PG15-44/68 groups, respectively). We concluded that any time between 56 and 68 h after PG15 protocol could be used to perform cervical TAI using fresh semen, without benefits of a double TAI service at 44 and 68 h.