Active immunization against inhibin-based peptides to increase ovulation rate in non-prolific Malpura ewes

The aim of this study was to explore the possibility of increasing the ovulation rate of Malpura, a non-prolific tropical breed of sheep by immunization against inhibin-based peptide immunogens. Ewes were divided into three groups (n = 5 each) and actively immunized against the synthetic peptides from the αC [bIα(1-29)-Tyr30] or αN [bI-43-Tyr152(153-167)Cys168] area of the bovine inhibin α-subunit conjugated to ovalbumin or against ovalbumin (control). Each ewe received a primary immunization of 400 μg immunogen and 3 boosters, each of 200 μg immunogen at 4-week intervals. Estrus was synchronized using a double PGF2α injection schedule and laparoscopy was performed after each estrus to determine the ovulation response. Immunization against both the peptides did not affect the interval from PGF treatment to the onset of estrus, the duration of estrus and the number of large unovulated follicles. In contrast to the complete absence of multiple ovulations in the controls, all the ewes immunized against αC or αN peptides showed multiple ovulations (range 2-7) in all the three estrous cycles evaluated, except for one ewe immunized against the αN peptide, which exhibited multiple ovulations in only 1 out of the 3 estrous cycles. Compared to that of the controls (1.0 ± 0.9, 1.0 ± 0.0 and 0.6 ± 0.2, respectively), the mean ovulation rate was higher (P < 0.01) in the ewes immunized against the αC (4.8 ± 1.02, 5.0 ± 1.05 and 5.0 ± 0.45, respectively) or against αN (4.5 ± 1.19, 2.5 ± 0.87 and 2.7 ± 0.75, respectively, P < 0.05) peptide in estrous cycles numbers 1, 2 and 3. These results show that active immunization against inhibin-based peptide immunogens is effective in increasing ovulation rate in Malpura, a non-prolific breed of sheep and that it may be an alternative to conventional superovulation regimes.