Polymorphism of bone morphogenetic protein 4 gene and its relationship with litter size of Jining Grey goats
The objective of this study was to determine the effect of passive immunization against estrone (E1), estradiol (E2) or estrogens (nonspecific; Ens) on ovulation rate and kidding rate in Angora does. On d 0 of the study, Angora does were divided into four treatment groups: 1) passively immunized against E1 (n = 14); 2) passively immunized against E2 (n = 24); 3) passively immunized against Ens (n = 9); and 4) injected with normal goat serum (control; n = 23). Fertile bucks were allowed to mate with the does from d 2 to 44. Immunization treatments did not influence (P greater than .1) percentage of does exhibiting estrus, percentage of does kidding or kid death rate. Ovulation rate was greater (P less than .06) in E2 and Ens immunized does than in control does. Both E2 and Ens treatments resulted in a greater (P less than .05) percentage of does giving birth to twins rather than singles compared with E1 or control treatments (70, 83, 27 and 31% twin births for E2, Ens, E1 and control, respectively). This increase in twin births resulted in kid crops per doe exposed of 142 and 122% for E2 and Ens compared with 100 and 91% for E1 and control treatments (P less than .05 for E2 vs control). These results demonstrate that the incidence of twin births can be increased by passively immunizing does against E2.