Hormonal treatments and the ram effect on synchronised oestrus in awassi ewes at the beginning of the breeding season

Abstract

Eighty-four Awassi ewes in five groups were used to study the effect of using different hormonal treatments or ram effect on oestrus synchronisation and fertility at the beginning of the breeding season. At the onset of the treatments, gonadotropin releasing hormone-prostaglandin F2α (Gn-PG, n = 17) ewes received gonadotropin releasing hormone (GnRH) i.m. followed with prostaglandin F2α (PGF2α) 5 days later. Ewes in the prostaglandin F2α-prostaglandin F2α (PG-PG, n = 20) group received two i.m. injections of PGF2α 10 days apart. Ewes in the fluorogestone acetate (FGA, n = 15) group were fitted with FGA intravaginal pessaries, left for 14 days and given an i.m. injection of pregnant mare serum gonadotropin (PMSG). Ewes in hormonal treatments (Gn-PG, PG-PG, FGA) and the Close (n = 17) group, were housed in a barn close to the rams’ barn for the last 15 days, while those in the Far (n = 15) group were left in a barn completely separated from rams until the day of mating. Ten fertile rams were introduced 48 h after the last treatments. Plasma progesterone (P4) concentrations were similar at the onset and at the last day of treatments for ewes in the five groups. On Days 8 and 11 (Day 0 = day of last treatment) a significant increase (P < 0.05) in P4 level was observed in the Gn-PG and PG-PG compared with the Close and Far groups. Plasma P4 remained higher in the Gn-PG and PG-PG, compared to the other groups through Days 17–20 post-treatment. The average oestrus response was 80% and similar in all groups. Pregnancy rate based on plasma P4 concentrations on Days 17 and 20 post-treatment were lower in the Close than other groups. The proportion of ewes observed in oestrus in the hormone treated groups tended to be greater (P < 0.1) than that in the non-hormone treated (Close, Far) groups. Pregnancy rate, based on P4 concentrations and lambing rate, were significantly greater (P < 0.05) in the treated groups than that in the non-treated groups, while lambing rate from ewes rebreeding was similar. Results indicate that Awassi sheep maybe synchronised using either GnRH-PGF2α program or two injections of PGF2α10 days apart as well as progestagen treatment, but with lower number of days required for synchronisation. Similar pregnancy and first lambing rates were observed in the treated groups and Far group, which may be due to the sudden introduction of rams to the last group, but the Close group was still low. © 2005 Taylor & Francis Group, LLC.