FERTILITY OF SUPEROVULATED EWES AFTER INTRAUTERINE OR OVIDUCAL INSEMINATION WITH LOW NUMBERS OF FRESH OR FROZEN-THAWED SPERMATOZOA

Two experiments investigated the effects of number of spermatozoa inseminated and time and site of insemination of fresh and frozen-thawed semen on fertility in Merino ewes treated with intravaginal progestagen pessaries and a combination of pregnant mare serum gonadotrophin and follicle stimulating hormone. In Experiment 1, ewes were inseminated in the uterus or oviducts with totals of 10(4), 10(5), 10(6) or 10(7) fresh spermatozoa 44 or 68 h after pessary removal. Ova recovered 48 h later were classified as fertilized if they had cleaved. Proportion of fertile ewes (ewes with fertilized ova per ewes inseminated) and fertilization rate of ova (ova fertilized per ova recovered) were higher for inseminations 44 h (63% and 45%) than 68 b (38% and 19%) after pessary removal (P<0.001). More ewes were fertile after oviducal (61%) than after intrauterine insemination (39%; P<0.05), and with high (10(6) and 10(7)) than with low (10(4) and 10(5)) doses of spermatozoa for intrauterine (54% v. 24%; P<0.05) but not for oviducal inseminations (63% v. 59%). Fertilization of ova was better after oviducal than after intrauterine inseminations (44% v. 22%; P<0.001), and with high than with low doses of spermatozoa (45% v. 21%; P<0.001). In Experiment 2, ewes were inseminated with 10(5), 5 x 10(5) or 10(6) total fresh or frozen-thawed spermatozoa in the uterus or oviducts, 44 h after pessary removal. Proportion of fertile ewes and fertilization rate of ova were higher for oviducal (75% and 59%) than for intrauterine inseminations (27% and 14%; P<0.001), and for fresh (56% and 35%) than for frozen-thawed semen (47% and 29%; P<0.05). Fertilization rate of ova was higher for inseminate doses of 5 x 10(5) and 10(6) than for 10(5) total spermatozoa (36% v. 25%; P<0.01). The study showed that fertilized ova can be obtained after deposition of 10(4) fresh spermatozoa in the oviducts of superovulated ewes, and that the minimum effective dose is between 10(5) and 10(6) fresh spermatozoa.