Effect of immunization against synthetic peptide sequences of the alpha N-subunit of bovine inhibin on ovulation rate, gonadotrophin concentrations and fertility in heifers.

The effects of immunizing cattle against either of two peptides from the amino terminal peptide (alpha N) of the alpha 43-subunit of bovine inhibin on ovulation rate, gonadotrophin concentration and fertility were investigated. Two peptide sequences from the alpha N-subunit of bovine inhibin (P1N, bI alpha-(8-20) and P2N, bI alpha-(153-167)) were synthesized and conjugated to human serum albumin (HSA). Hereford-cross heifers (n = 5 per group) were given an initial injection of 3 mg of one of the peptide conjugates, followed by three booster injections (1.5 mg) at intervals of 11 weeks. Control heifers (n = 5) were injected with HSA only. Blood samples were taken once a week to measure antibody titre and every hour at about the time of the first oestrus and during the mid-luteal phase after the second booster injection, to measure FSH and LH concentrations. Ovulation rate was measured by ultrasonography. Gonadotrophin concentrations were analysed for four periods relative to the peak (time = 0 h) of the preovulatory LH surge as follows: pre-surge: -16 to -5 h; surge: -4 to 4 h; post-surge: 5 to 16 h and a period of 12 h during the mid-luteal (days 10-12) phase. Antibodies that bound to the individual peptides were generated and the ovulation rate increased (P < 0.05) in immunized heifers. Control heifers had one ovulation at all ovulatory cycles monitored. In group P1N, one heifer had two ovulations at each of the six cycles monitored, while another heifer had two ovulations at one cycle.(ABSTRACT TRUNCATED AT 250 WORDS)