The long-term effect of active immunization against inhibin in goats

This experiment addresses the long-term effect of active immunization of goats against a recombinant ovine inhibin α subunit (roIHN-α). In late anestrus 100 μg of roINH-α was administered to 40 pluriparous Boer goat does, followed, 4 weeks later, by a booster injection. Weekly blood samples were drawn to monitor the inhibin binding capacity with the aid of a radio-tracer binding assay. From the onset until 48 h after the end of each estrus, follicular development and ovulation rate were monitored at 24 h intervals by transrectal ultrasonography. Beginning in August and continuing into January, does were mated at every other estrus, and submitted to transcervical embryo collection. Seven months after the first immunization, the does were mated again and permitted to carry to term. All immunized does produced inhibin antibodies, an elevated titre being first detected 2 weeks after primary immunization. Maximum titres were reached after 6 weeks, i.e. 2 weeks after the booster injection. Thereafter, in the course of the following 32 weeks, the titre subsided gradually. The does started cycling by mid-August. At that stage the average number of follicles more than 4 mm in diameter, ovulations and total embryos and ova recovered were 14.7 (±2.3), 5.3 (±0.7) and 4.4 (±1.0), respectively. A steady decline followed and in January the corresponding means were: 5.2 (±0.6) follicles, 3.1 (±0.6) ovulations and 1.2 (±0.4) embryos and ova recovered. When mated toward the end of the breeding season, 85% of the does became pregnant to the first mating and 73% went to term. Healthy kids were born, the average litter size being 2.2 (±0.1). In conclusion, immunization of goats against a recombinant inhibin α-subunit proved to be a practicable means of producing embryos for transfer purposes. After about half a year, when the inhibin antibody titre has subsided, it is possible to return the does to the breeding flock without risking complications with normal breeding activity.