Artificial Induction of Twinning by an Active Immunization of Beef Cows Against Inhibin Partially Purified from Porcine Seminal Plasma

Two hundred and seventy multiparous Chinese Yellow cattle (beef) were selected at 1 to 3 months postpartum and divided into three groups (90 cows for each). Animals were given both a primary and booster immunizations with a total dose of 3mg (Group Th) or 1.5 mg (Group TI) of seminal preparation containing inhibin activity, emulsified with Freund's complete adjuvant and incomplete adjuvant (for booster), at 3 or 4-week intervals. Other cows were treated with the same volume of seminal preparation without inhibin activity as procedures mentioned above to serve as a control (Group C). Artificial inseminations were given twice at 8-12 h intervals when the cow was in heat. Jugular venous blood samples were collected from each cow and used to assay the presence of antibody against seminal preparation by double-diffusion in agar precipitation test and to detect the titer of inhibin antibody by an ELISA method. Data from 247 cows showed that 83.9% (73/87) of cows were in estrus and ovulated 89 ova altogether, of which 19 cows ovulated twin ova and 15 cows produced twins in Group Th (n=87). However, only 61.1% (44/72) of cows in Group Ti (n=72) and 62.5% (55/88) of cows in Group C were in estrus and ovulated 46 and 52 ova altogether respectively. The ovulation rate (1.27±0.03), calving rate (126.3%) and twinning rate (26.3%) in Group Th were greater than those in Groups TI or C (P＜0.01). Furthermore, the ovulation rate was associated with antibody titer in sera of immunized animals (r=0.7507, P＜0.01). These results indicate that active immunization of postpartum cows against inhibin purified from porcine seminal plasma may increase the ovulation rate and induce twinning, suggesting the potential to develop a method to improve fertility in cows.