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.