Fertility of the frozen ram semen

Semen was collected form 5 Welsh Mountain rams by means of an artificial vagina. After evaluation, semen was pooled and diluted with tris-based diluent at 1:2 (semen: diluent). The diluted semen was cooled to 5øC over 2 hr and frozen either in straws or as pellets. Welsh Mountain ewes (217) were synchronized using sponges impregnated with medroxyprogesterone acetate for 12 days. On sponge withdrawal each ewe received a 350 i/u PMSG by subcutaneous injection. Inseminations were carried out 56 hr after sponge withdrawal. In trial 1, thawed semen which was frozen in straws or as pellets (400x106 sperm/dose) was introduced into the first fold of the cervix. In trial 2, inseminations were carried out at either cervix, vagina, intrauterine or on the ovary. Higher fertility results were obtained after insemination with semen frozen as pellets than in straws, however, the differences were not significant. Frozen semen exhibited reduced fertility (P0.5) when compared with fresh semen. Lambing rates showed highly significant (P0.001) differences due to the sites of semen deposition. The fertility results following intrauterine insemination with frozen semen were significantly higher (P0.05) than for cervical or vaginal insemination. Lambing results obtained following intrauterine insemination with frozen semen was effective as cervical insemination with fresh semen. The inseminated sperm number into the uterus had no significant effect on lambing percentage. The results following semen deposition on to the ovaries were nil, therefore this treatment was excluded from the data analysis.