ADVANCEMENT OF PUBERTY IN EWE LAMBS BY ACTIVE IMMUNIZATION AGAINST INHIBIN EARLY IN LIFE

Active immunisation of lambs early in life with inhibin can advance pu berty and increase ovulation rate but these effects appear not to be m ediated through changes in FSH concentrations. The aims of this study were to advance puberty in ewe lambs and determine if increased plasma concentrations of gonadotropins are responsible for the advancement o f puberty. Ewe lambs were immunised at 3, 7 and 15 weeks of age agains t either a synthetic inhibin alpha subunit peptide 1-32 conjugated to human serum albumin (HSA), or an inhibin preparation purified from por cine follicular fluid (porcine monoclonal purified inhibin; pMPI), or HSA alone (control immunogen). Immunisation with inhibin alpha peptide 1-32 produced antibodies which bound iodinated native bovine inhibin and advanced puberty (time of first ovulation) and increased ovulation rate but did not significantly increase plasma FSH concentrations, al though LH concentrations were lower (P < 0.01) on a number of occasion s. In contrast, immunisation with pMPI significantly (P < 0.01) increa sed FSH and LH concentrations following the first booster immunisation , although FSH was only transiently elevated. Despite these increases in gonadotropins, no advancement of puberty was observed in PMPI immun ised ewe lambs. This study confirms that active immunisation of ewe la mbs early in life against inhibin advances puberty via a mechanism whi ch does not significantly increase plasma gonadotrophin concentrations . Immunisation to advance puberty also results in persistent increases in ovulation rates in later breeding seasons.