The acceptance and antifertility action of microencapsulated diethylstilbestrol (DES) administered in feed was investigated with penned female white-tailed deer (Odocoileus viirginianus). A switchback designed oral acceptance test at 0, 250, 500, 750, and 1,000 mg was conducted just before the breeding season. The 1,000 mg level was as well accepted as the other three concentrations, but none were as well accepted as the control. Six does were presented 1,000 mg of DES, homogenized in 1.362 kg of feed, every 17 days throughout the breeding season. Five of the six does demonstrated aversion to the compound. Consumption of 131mg or less did not prevent normal pregnancy. The sixth doe, which consumed 182 and 428mg at the first two feedings, bred again after each feeding indicating that these levels might have interrupted pregnancy. Possible reasons for the poor acceptance of DES during the breeding season are discussed. If the rejection is due to metabolic aversion, microencapsulated DES may never work as a multiple-dose antifertility agent; if it is due to taste or smell, a different microencapsulation formulation might overcome the aversion problem.
