Effects of a Dietary Combination of Diethylstilbestrol and Methyltestosterone on Reproductive Performance of Gilts

One hundred thirty-six gilts were used in five experiments to study the effects on reproductive performance of feeding 2.2 or 4.4 mg. each of diethylstilbestrol (DES) and methyltestosterone (MT) per kg. of diet during the finishing phase only or continuously through finishing to breeding. Feeding the hormonal combination through breeding inhibited estrus. Some gilts conceived after termination of hormone administration. Gilts which received hormonal treatment only during the finishing phase had normal estrous cycles, and conception rate was reduced in only one of three experiments. In four of five experiments, prior oral administration of DES+MT reduced litter size. It was observed that gilts fed the hormonal combination during the finishing period farrowed smaller litters at the first two parturitions. However, litter size was equal to that of control gilts at the third parturition. Thus, inhibition of reproductive function by hormonal treatment during finishing did not appear to be permanent. The lower level of additives did not appear to be as inhibitory to reproductive performance as the higher level.