Ram seminal plasma and fertility: results from an ongoing field study

The effects of partial replacement of ram semen diluent with ram seminal plasma on the fertility of ewes were studied. Crossbred Chios ewes (n = 152) were assigned to six groups. The oestrous cycles of the ewes were synchronised at the peak (Groups A, B, C and D) and at the end (Groups E and F) of the breeding season by means of intravaginal sponges impregnated with fluorogestone acetate (FGA) for 14 days. Four hundred IU of PMSG were injected intramuscularly at the time of sponge removal. Ewes of Groups A, C and E were artificially inseminated with ram semen diluted with skim milk extender, while those of Groups B, D and F with ram semen diluted with 50% skim milk and 50% ram seminal plasma. The addition of ram seminal plasma induced a significant increase (P < 0.05) in litter size in Groups B and D when compared with that of Groups A and C (1.85 and 1.88 vs. 1.39 and 1.52, respectively). This increase was not significant when insemination was performed at the end of the breeding season (2.0 vs. 1.4). These results indicate that the addition of seminal plasma can influence the fertility of ewes or the fertilising capacity of extended ram semen to some extent.