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 inse minated and time and site of insemination of fresh and frozen-thawed s emen 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 i n the uterus or oviducts with totals of 10(4), 10(5), 10(6) or 10(7) f resh 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 fert ilization rate of ova (ova fertilized per ova recovered) were higher f or inseminations 44 h (63% and 45%) than 68 b (38% and 19%) after pess ary removal (P<0.001). More ewes were fertile after oviducal (61%) tha n 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 in trauterine (54% v. 24%; P<0.05) but not for oviducal inseminations (63 % v. 59%). Fertilization of ova was better after oviducal than after i ntrauterine inseminations (44% v. 22%; P<0.001), and with high than wi th low doses of spermatozoa (45% v. 21%; P<0.001). In Experiment 2, ew es were inseminated with 10(5), 5 x 10(5) or 10(6) total fresh or froz en-thawed spermatozoa in the uterus or oviducts, 44 h after pessary re moval. Proportion of fertile ewes and fertilization rate of ova were h igher for oviducal (75% and 59%) than for intrauterine inseminations ( 27% and 14%; P<0.001), and for fresh (56% and 35%) than for frozen-tha wed 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 sperm atozoa (36% v. 25%; P<0.01). The study showed that fertilized ova can be obtained after deposition of 10(4) fresh spermatozoa in the oviduct s of superovulated ewes, and that the minimum effective dose is betwee n 10(5) and 10(6) fresh spermatozoa.