Oestrous Synchronization of Ewes, Using Norgestomet Combined with PGF₂ and hCG in the Reproductive Season

To determine if with doses of norgestomet (N) at lower (3 mg) and shorter treatment time to that normally used (9 d), estrous can be induced, with the aim to reduce synchronization costs without altering main reproductive variables, 24 Dorset ewes were randomly assigned to four treatments (T, n = 6): T1) 3 mg of N for 9 d; T2) 2 mg of N for 9 d; T3) 3 mg of N for 7 d and T4) 2 mg of N for 7 d, all groups received an intramuscular (i.m.) PGF2 (15 mg) injection 2 d before implant removal and on the day of the removal received 1000 U.I. of human Chorionic Gonadotrophin (hCG) i.m. There was a 66% of estrous onset in T1, 83% in T2 and 33% in T4. Average progesterone (ng mL 1) concentration was higher in T2 (p< 0.05), although life span of the corpus luteum was similar between treatments. Lambing rate were higher in T2 (60%) compared to T1 (50%). Under the conditions of the present experiment a dose of N lower than 3 mg does not affect main reproductive variables in the reproductive season.