EFFECT OF IMMUNIZATION OF EWES AGAINST ALPHA-1-26 INHIBIN FRAGMENT ON ANTIBODY-TITERS, OVULATION AND LAMBING RATE

Inhibin is involved in the regulation of follicle stimulating hormone (FSH) secretion and thus has a role in controlling the rate of ovulation. Immunisation of ewes against specific fragments of inhibin increases the ovulation rate. The aims of this study were to determine the persistency of antibody titres and changes in ovulation and lambing rates following immunisation against a 1-26 inhibin fragment conjugated to human serum albumin and given in non-ulcerative Freunds adjuvant. In Experiment 1, 38 multiparous ewes were randomised and either immunised (primary on Day 0 with a booster 1 month later) against 0.33 mg inhibin conjugate or left untreated. Weekly blood samples were collected to determine antibody titres at a dilution of 1:2000. The ovaries were examined by laparoscopy on eight occasions between Days 50 and 192. Antibody titres rose significantly in the immunised ewes after booster injection and remained high throughout the experiment. Seven (37%) immunised ewes demonstrated over 20% maximum binding of radiolabelled inhibin, and a further four (21%) ewes had more than 1O% binding. There was a significant (P0.05) increase in ovulation rate in immunised ewes on each occasion. Six (32%) ewes had superovulatory responses (five or more ovulations) on repeated occasions following immunisation. A log-linear model showed a significant positive association between ovulation rate and antibody titre. The superovulatory response to exogenous equine chorionic gonadotrophin (eCG) treatment was not different in control and immunised ewes.In Experiment 2, 58 adult ewes were used and 29 were immunised as in Experiment 1. Air ewes were treated with 60 mg medroxy progesterone acetate pessaries for 14 days; control ewes received 650 IU eCG at pessary withdrawal while immunised ewes received no gonadotrophin; rams were joined 2 days after pessary withdrawal. There was no difference in conception rates (86% vs. 90%) between control and immunised ewes. However, litter size to first service (2.35+ -0.16 vs. 1.76+ -0.16, P=0.016) and second service (2.66+ -0.33 vs. 1.50+ -0.28, P=0.046) was increased in immunised ewes. The results of these experiments demonstrate that immunisation against a 1-26 inhibin fragment increased ovulation rates from September until February and increased litter size, without having any effect on conception rate in synchronised ewes.