MODULATION OF OVARIAN-FUNCTION BY STEROID AND INHIBIN IMMUNIZATION

Immunization against steroids and inhibin have been used to improve go nadal function. In the ewe, steroid immunization increases ovulation r ate. The mechanisms of this increase are not fully understood, but inv olve a reduction of the atresia of ovarian follicles, an increase in t he number of LH pulses and presumably modification of the local action of steroids. Within a range of steroid antibody titre, an increase of the litter size is generally observed (0.1 to 0.7 lambs), but the gai n in extra lambs decreases when natural prolificacy increases or when the antibody titre is too high. In ewes, immunization against recombin ant inhibin or against an a subunit synthetic peptide increased FSH, o vulation rate and litter size. In porcine and bovine species, immuniza tion against inhibin also increases ovulation rate. Thus, these two ap proaches have the potential to increase the efficiency of lamb product ion but genotypes, feeding levels and management have to be adapted fo r these methods to be beneficial.