The Effect of PMSG on Follicular Development and Ovulation Time of PGF2 Treated Awassi Ewes

Abstract

The objective was to examine the effects of PMSG administration before or at the time of PGF2α injection on reproductive responses of ewes out-of-season. In late June and early July, 57 anestrus ewes were induced to estrus using CIDR-G devices for 12 days. Six days following device removal ewes were randomly allocated into three treatment groups and each received an i.m injection of 20mg PGF2α (day 0, 0 h). PMSG (500 IU) was administered either 24 h before (group A, n=20) or at (group B, n=19) the time of PGF2α injection. Group C ewes (n=18) served as control. Half of the ewes in each group were exposed to three intact rams at 0 h to be naturally mated and the other half were exposed to three aproned rams and inseminated 50-56 h following 0 h. Ewes were checked for breeding marks at 6-h intervals for 4 days. Progesterone levels from day –1 until day 20 were monitored. Occurrence of estrus was similar among ewes of the three treatment groups and averaged 79%. PMSG-treated ewes had shorter (P<0.01) intervals to estrus and ovulation, and a higher ovulation rate than non-PMSG treated ewes. Pregnancy and lambing rates were similar among PMSG- and non-PMSG-treated ewes. Although reproductive responses were similar among artificially-inseminated and naturally-mated ewes, the latter had a higher (P<0.05) lambing rate (14.3% vs 41.4%, respectively). Ewes inseminated close to the time of ovulation (7.7 h earlier) produced higher (P<0.05) pregnancy rate than those inseminated at a wider interval from ovulation (16.7 h earlier). In conclusion, the PGF2α treatment given during luteal phase was effective in resetting subsequent cyclic activity of ewes. Although it did not increase the number of ewes detected in estrus, PMSG shortened intervals to estrus and ovulation, increased ovulation and induced–estrus pregnancy rates.