The effect of immunization of heifers against alpha 1-26 inhibin conjugate on the superovulatory response to pFSH

A total of 121 heifers was blocked by time and diet and then randomly assigned, within block, to an inhibin-immunized (I) or a control (C) group. Immunized heifers (n=61) received a primary immunization (Day 0) with 0.33 mg of an alpha 1-26 bovine inhibin fragment-human serum albumin (HSA) conjugate injected with non-ulcerative Freund’s and DEAE-dextran adjuvants. Booster injections were given on Days 28 and 56. Control heifers (n=60) received HSA and adjuvants. On Days 56 and 83 the ovaries of heifers were examined by ultrasound to determine the ovulation rate, and blood samples were collected for antibody titer determination. On Day 84, 61 heifers (C, n=30 ; I, n=31) received a total of 24 mg of porcine follicle stimulating hormone (pFSH), while 60 heifers (C, n=30; I, n=30) received 12 mg im pFSH, which was administered twice daily for 4 d in decreasing doses during the mid-luteal phase of the estrous cycle. Luteolysis was induced with prostaglandin F2alpha analog. The heifers were artificially inseminated and were slaughtered 7 d after estrus. Embryos were recovered and morphologically graded on a scale of 1 to 5 (1=excellent; 5=degenerated). Antibody titers (percentage binding at 1: 125 serum dilution) differed (P<0.01) between Group C and I heifers at Days 56 (0.1 vs 30%) and 83 (0.2 vs 37%), and 26% of Group I and 1% of Group C heifers (P<0.01) had twin ovulations on Day 83 . The mean number of embryos recovered was reduced (P=0.02) in Group I heifers (8.9±1.2) compared with C heifers (12.1±1.1); however, the mean number of freezable embryos (Grades 1 and 2) was not affected (P=0.61) by immunization, and there was no interaction with pFSH (P=0.36). Ovulation rate as well as embryo yield and quality were not different (P>0.10) between Group C and I heifers when 12 mg pFSH were administered; however, immunization decreased the superovulatory response to 24 mg of pFSH.