Active immunization with a synthetic fragment of pig inhibin α-sub unit increases ovulation rate and embryo production in superovulated ewes but season affects its efficiency

Abstract

Two experiments were designed to determine the effects of active immunization against one of two synthetic peptides from humans (inhibin-like peptide) or pigs (inhibin α-subunit) on antibody titres, ovulation rate and embryo production in ewes superovulated with 16 U ovine FSH. In Expt 1, during the breeding season, 30 ewes were subdivided into three groups: group I served as the non-immunized control; group II was immunized against inhibin-like peptide (100 μg inhibin-like peptide equivalent, followed by three booster injections); group III was immunized against pig inhibin α-subunit conjugated to human serum albumin (96 μg for the primary administration and 46 μg for the booster). In Expt 2, the efficiency of immunization against pig inhibin α-subunit on ovarian response and embryo production was evaluated during the non-breeding season in two groups of ewes (n = 12): group IV was a non-immunized control; Group V was immunized against pig inhibin α-subunit. During the breeding season, the ewes immunized against pig inhibin α-subunit showed higher antibody titres compared with the group immunized against inhibin-like peptide (P < 0.01) and a significant increase in ovulation rate (12.1) compared with both the control (5.0; P < 0.05) and the inhibin-like peptide-immunized group (3.1; P < 0.01). Immunization against pig inhibin α-subunit increased transferable embryo yield 4.5-fold (6.7 versus 1.5; P < 0.01) and improved embryo quality (94.6 versus 40.6%; IV 0.01). During the non-breeding season, immunization against pig inhibin α-subunit enhanced ovulation rate from 2.6 in the controls to 9.4 (P < 0.01) but did not affect transferable embryo production (3.9 versus 2.1; P 0.05) and significantly lowered their quality (54.1 versus 100%; P< 0.01). In conclusion, active immunization against pig inhibin α-subunit can improve superovulatory response during the breeding season, while it appears to be unable to increase embryo yield during the seasonal anoestrus.