Long interval prostaglandin as an alternative to progesterone-eCG based protocols for timed AI in sheep

•Long PG intervals were associated with higher non return and pregnancy rates.•Long PG intervals equates progesterone-eCG fertility, prolificacy and fecundity.•Ovulating ewes was not affected by the protocol used.

To compare the reproductive performance after TAI in ewes synchronized with mid (12 or 13) or long (14-16 d) interval prostaglandin (PG) or progesterone plus eCG (P4-eCG) based protocols, 440 multiparous Corriedale ewes were synchronized with two PG injections administered 12-16 d apart (PG12, PG13, PG14, PG15 and PG16 respectively), or P4-eCG (MAP sponges 14 d and eCG). Cervical TAI (Day 0) was performed with fresh semen. It was evaluated the ovulated ewes (OE, %) and the ovulation rate (OR) on Day 8 by trans-rectal ultrasonography, the rate of non-return to service between Days 13 and 21 by painted rams, and the pregnancy rate, prolificacy and fecundity on Day 60 by trans-abdominal ultrasonography. No significant differences were found in OE among groups (P > 0.05), but P4-eCG achieved higher OR (P < 0.05) compared to PG protocols, without differences among them (P > 0.05). Similar NRR-21, pregnancy and fecundity were observed among PG15 (64.3, 62.9 and 84.3), PG16 (59.7, 59.7 and 77.8) and P4-eCG (70.3, 66.2 and 95.9), but higher compared to PG12 (42.5, 39.7 and 52.1) and PG13 group (44.0, 40.0 and 48.0, respectively; P < 0.05). PG14 achieved intermediate results compared to other groups. No differences were found in prolificacy among groups (P > 0.05), except PG13 that was lower compared to P4-eCG (P < 0.05). In conclusion, long interval between PG injections (15 or 16 d) determined better reproductive outcome that mid interval (12 or 13 d), equating the P4-eCG based protocol after cervical TAI with fresh semen during the breeding season in sheep.