Studies on enhancing embryo quantity and quality by immunization against inhibin in repeatedly superovulated Holstein heifers and the associated endocrine mechanisms

Abstract

To investigate the feasibility of improving embryo production in cattle by immunization against inhibin, both in vivo and in vitro experiments were conducted. In two experiments conducted in two autumns, 14 animals aged 14 months were immunized with a recombinant inhibin α subunit protein antigen for four times at monthly intervals, with another 14 animals of the same age served as the controls. Starting from the second immunization, all the heifers received standard superovulation treatment for three sessions, one session per month, each starting 10 days after every antigen administration. Immunization against inhibin increased number of transferable embryos (P<0.05), and high quality Grade A embryos (P<0.01) in each superovulation. Blood concentrations of FSH, estradiol, activin, and also ratio of activin to follistatin concentrations were greater in inhibin immunized than in control animals during the period of superovulatory FSH administration and animal estrous expression. Heifers immunized with inhibin also had greater concentrations of progesterone in the later diestrus period. In the second experiment, the inclusion of anti-inhibin antibody in oocyte IVM medium increased oocyte maturation rate and cleavage rate following IVF (P<0.05). These results demonstrated that inhibition of the adverse effects of inhibin on ovarian follicular development and oocyte maturation improved embryo yield, in both quantity and quality, following superovulation. These results also demonstrate that active immunization against inhibin, in conjunction with the conventional superovulation protocol, can constitute a new technique for consistent improvement of bovine embryo production in vivo; while passive immunization with anti-inhibin antibody can improve embryo production in vitro.