INCREASED OVULATION RATES IN PMSG-STIMULATED BEEF HEIFERS TREATED WITH A MONOCLONAL PMSG ANTIBODY

The effects of PMSG dose and monoclonal anti-PMSG treatment on the sup erovulatory response were investigated in beef heifers. Heifers were a dministered 1500 (n=22), 3000 (n=21) or 4500 (n=21) IU of PMSG on Day 8, 9 or 10 after estrus, and half of the heifers in each group receive d a neutralizing dose of anti-PMSG at the time of first insemination ( 60 h after prostaglandin treatment). Overall, the anti-PMSG-treated he ifers had more ovulations, fertilized ova, and transferable embryos wi th fewer unovulated follicles than heifers treated with PMSG alone (P< 0.05). Although, only heifers treated with 3000 IU PMSG plus anti-PMSG had more ovulations (P<0.03) and fewer unovulated follicles (P<0.02) than the corresponding PMSG-only controls, anti-PMSG treatment increas ed total ova/embryos (P<0.002) and transferable embryos (P<0.003) for the 2 lowest PMSG doses and fertilized ova (P<0.001) for all 3 PMSG do ses. Preovulatory plasma estradiol levels increased (P<0.05) with PMSG dose until Day 4 and were correlated with number of ovulations and un ovulated follicles in the PMSG-only heifers (r=0.96, P<0.02) and with the number of ovulations in the anti-PMSG-treated heifers (r=0.99, P<0 .025). Plasma estradiol remained elevated for 24 h after the onset of estrus and then declined to baseline by 48 h after estrus in the anti- PMSG-treated heifers, estradiol declined slightly and then increased a gain during the same period in heifers treated with PMSG alone. This p ost-ovulatory increase In estradiol was inversely correlated with ovul ation (P<0.003) and fertilization (P<0.03) rates. These data indicate that with a 3000 IU PMSG dose, administration of PMSG monoclonal antib ody increased ovulations, fertilized ova and transferable embryos.