INHIBIN IMMUNIZATION FOR INCREASING OVULATION RATE AND SUPEROVULATION

The paper reviews the role of inhibin in the ruminant estrous cycle an d the potential of inhibin vaccines in sheep and cattle to increase ov ulation rate, fecundity and reliability of superovulation in embryo tr ansfer programs. Immunization of ewes with various inhibin preparation s (native inhibin, synthetic peptides or recombinant inhibin-alpha fus ion proteins) resulted in an increased ovulation rate, that can be att ributed to elevated plasma FSH concentrations. Persistent superovulato ry responses were obtained with synthetic peptides. The ovulation rate increases obtained with inhibin immunization and exogenous FSH were s hown to be additive so that less exogenous gonadotrophin is required t o obtain a given ovulation rate and hence embryo recovery rate. In cat tle a prototype vaccine has been developed, based on small doses of re combinant ovine inhibin-alpha protein. This results in raised plasma F SH concentrations and increased ovulation rates after booster vaccinat ions. Unlike in sheep, synthetic peptide immunization has not, so far, given a satisfactory superovulatory response. Preliminary evidence is reviewed showing that inhibin immunization should also result in less exogenous gonadotrophin being required in embryo transfer programs in cattle.