SUPEROVULATION IN THE COW WITH PREGNANT MARE SERUM GONADOTROPIN - EFFECTS OF DOSE AND ANTIPREGNANT MARE SERUM GONADOTROPIN SERUM

The effects of pregnant mare serum gonadotrophin (PMSG) dose and PMSG antiserum on superovulation in crossbred beef cows were studied. In ex periment I, three groups were treated with 1200, 2400 or 3600 IU of PM SG and 48 h later with prostaglandin (PGF). The mean numbers of corpor a lutea (CL), unovulated follicles, and total ova/embryos collected in creased as the PMSG dose increased. The percent of fertilized ova and transferable embryos was lowest in the highest dose group (p<0.05). In experiment II, all cows received 2500 IU of PMSG; groups 1 and 2 were treated with sheep anti-PMSG serum at 48 h or 60 h after PGF; group 3 cows were PMSG-only controls. The number of CL was lowest and the num ber of unovulated follicles highest in the PMSG-only group (p<0.05). T he number of CL was higher in group 2 (anti-PMSG at 60 h) than in the control group, with the anti-PMSG at 48 h not different from the other groups. Numbers of total ova/embryos, fertilized ova, and transferabl e embryos were higher (p<0.05) in both antiserum-treated groups relati ve to the PMSG-only group. We conclude that superovulation of beef cow s with PMSG and treatment with PMSG antiserum will induce a higher sup erovulatory response and will result in higher CL numbers and fewer un ovulated follicles. Further, the variability in the superovulatory res ponse to PMSG treatment was still evident when PMSG anti-serum was adm inistered.