EFFECT OF ACTIVE IMMUNIZATION AGAINST THE AMINO-TERMINAL PEPTIDE (ALPHA-N) OF THE ALPHA-43-KDA SUBUNIT OF INHIBIN (ALPHA-43) ON FERTILITY OF EWES

Immunization against the amino-terminal peptide (alpha N) of the alpha 43 subunit of inhibin was shown previously to reduce fertility in ewe s. The aim of this study was to examine the effects of active immuniza tion of ewes against alpha N on egg recovery and fertilization rates. Ewes were immunized against alpha N immunogen, and were given 800 I.U. of pregnant mare's serum gonadotrophin at the end of treatment with i ntravaginal progesterone to synchronize the oestrous cycles. Control e wes received adjuvant only. The ewes were run with fertile rams, and 4 days after withdrawal of the progesterone device the oviducts were fl ushed to recover eggs and luteal structures on the ovaries were record ed. Eggs were recovered from 17/19 (90%) control ewes compared with 4/ 16 treated ewes (25%) (P < 0.01), and the egg recovery rates were 76% (45/59) and 17% (7/42) respectively (P < 0.001). The mean number of co rpora lutea (CL) per ewe were similar (3.1+/-1.4 v. 2.6+/-1.0) but sev eral CL in the treated ewes did not appear to have ruptured, and 2 tre ated ewes had cystic follicles and no CL. There were no apparent diffe rences in either the fertilization rates or the stages of development of fertilized eggs between treated and control ewes. Antibody binding levels in follicular fluid were approximately half those found in peri pheral plasma. It is concluded that immunization of ewes against alpha N leads to lowered fertility by suppressing ovulation, implicating al pha N in the normal ovulatory process.