Successful induction of oestrus,ovulation and pregnancy in adult ewes and ewe lambs out of the breeding season using a GnRH + progesterone oestrus synchronisation protocol

A series of experiments was designed to assess the effect of a treatment protocol(U-synch) for inducing oestrus and ovulation out of the breeding season in adult ewes and ewe lambs. The protocol consisted of a 7-day treatment with an intravaginal progesterone-releasing device (IPRD), administration ofGnRH at IPRD insertionon Day 0,and equine chorionic gonadotropin (eCG) and prostaglandin F2 at IPRD removal on Day 7. In Experiment 1, 50 or100 g GnRH were sufficient to induce ovulation at the beginning of the protocol in 3/9 and 4/9 ewes, respectively; while the resulting proportion of sheep ovulating after the treatment protocol was 88.9% and 77.8% in ewes initially treated with 50 or 100 g GnRH, respectively. In Experiment 2, the proportion of Romney-cross ewe lambs ovulating was greater(P < 0.0001) in the U-synchgroup(95.4%) than in the untreated Control group (3.2%). In Experiment 3, pregnancy rates of Dorset-cross sheep in the U-synch( 60.7%) and Standard (12-day IPRD and eCG treatment; 56.5%) groups were greater (P = 0.01) than in the untreated Control group(43.4%).The incidence of twin pregnancies was greater(P = 0.005) in the U-synch group than in the Control group. A 7-day IPRD treatment including GnRH treatment at device insertion and eCG treatment at device removal induced oestrus and ovulation during the non-breeding season in a high proportion of mature ewes and ewe lambs. High pregnancy rates to natural mating, with a low rate of triplet pregnancies, were also observed.