Influence of sperm number and seminal plasma on fertility of progestagen-treated sheep in confinement

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Abstract
Progestagen-impregnated vaginal sponges + PMSG [pregnant mare''s serum gonadotropin] were used to synchronize estrus in crossbred adult ewes which were inseminated 56 h after sponge removal with 0.5 ml diluted semen containing 400, 200, 100, 50 or 25 .times. 106 spermatozoa per insemination. The diluent was skim milk-citrate or pooled seminal plasma. There was no difference in reproductive performance due to the insemination medium. Fertility (no. of ewes lambing) after insemination of 400 or 200 .times. 106 spermatozoa was 68% and was similar to that observed after natural service at progestagen-induced estrus. When .ltoreq. 100 .times. 106 spermatozoa were inseminated, fertility fell markedly and the number of lambs per ewe inseminated decreased. A decrease in litter size also occurred. Insemination of 200 .times. 106 spermatozoa, i.e., < 10% of the number in a single ram ejaculate, allows normal conception rates in progestagen-treated ewes.