Field synchronization of Ethiopian Highland sheep for fixed time artificial insemination: improvement of conception rate with a double injection of prostaglandin at 11 days

The study investigated, for fixed time artificially inseminated (AI) Menz ewes in field trials, the reproductive performance of prostaglandin-based treatments simultaneously to the standard 'P-4+eCG' protocol. A total of 483 Menz ewes were assigned to either the 'P-4+eCG' protocol, using progesterone impregnated intravaginal sponges in combination with equine chorionic gonadotropin (eCG) injection at sponge withdrawal, or the 'PGF(s)' treatment where sheep received a single injection of prostaglandin or 'PGF(7)' and 'PGF(11)' where ewes were synchronized with 2 injections of prostaglandin 7 or 11 days apart, respectively. AI was implemented with fresh semen at 55 +/- 1 h after the end of the hormonal treatment. Conception rate (CR; 60.87 +/- 4.2) was highest for PGF(11)ewes (P < 0.05); PGF(s)ewes had the lowest CR (34.07 +/- 4.1). Other factors did not affect variation in CR (P > 0.05). A higher proportion of ewes in the P-4+eCG group yielded twins and triplets compared to the 3 prostaglandin-based protocols (P < 0.01). Nevertheless, a higher (P = 0.02) proportion (17.11 +/- 4.3) of PGF(11)ewes yielded twins by comparison to their PGF(7)counterparts (2.50 +/- 2.5). PGF-based protocol with 2 injections 11 days apart, preceded by a careful selection of non-pregnant ewes for cervical fixed-time AI, is a feasible reproductive management for sheep breeding programmes in Ethiopia.