COMPARISON OF TWO METHODS OF SYNCHRONIZING ESTRUS AND SUBSEQUENT LAMBING IN A COMMERCIAL SHEEP FLOCK

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Abstract
Ewes of a commercial sheep flock were treated with either two 15-mg intramuscular injections of prostaglandin F2α (PGF2α), 11 days apart, or vaginal sponges impregnated with 40 mg fluorogestone acetate (FGA) in place for 12 days to compare the two methods of synchronization of estrus. Each treatment was imposed on two subgroups of 36 ewes commencing on various days of an 8-day period so that maximum available ram power could be used. A third group of 38 ewes was not treated (controls). At lambing time, the duration of lambing and distribution of lambings for the treated and control ewes were compared. There was no significant difference (P > 0.05) in the proportions of ewes responding over a 6-day period to the PGF2α (84%) and FGA (89%) treatments. Similarly, there was no difference (P > 0.05) in fertility between the two treatments, PGF2α (63%) and FGA (78%). The 38 control ewes were bred over a 15-day period and 60% lambed to the first service. This was not different (P > 0.05) from the combined fertility (67%) of ewes responding (synchronized) to either treatment. All of the pregnant ewes that had been synchronized for estrus by either treatment lambed over a 22-day period with (83%) lambing within an 8-day period. The 21 control ewes pregnant to a first service lambed over a 19-day period; however, only 67% lambed in the above corresponding 8-day period. Prolificacy did not differ between the two treatments (both were 1.3), or between the treated (1.3) and non-treated ewes (1.4). PGF2α can be used effectively as an alternative to FGA for synchronization of estrus in ewes during the breeding season. Even though the synchronization of estrus was staggered over an 8-day period, the resulting condensation of the lambing interval of the treated ewes proved to be beneficial in the commercial sheep operation.

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