Fertility Control in White-Tailed Deer by Steroid Implants

Abstract

Estrogen (DES), progestin (DRC-6246), or placebo tube-type Silastic? implants were placed subcutaneously in female white-tailed deer (Odocoileus virginianus) before the breeding season. No treated deer were pregnant after the breeding season. The daily release rates averaged 193 gtg (estrogen) and 93 g (progestin). The progestin-treated ovaries were characterized by large cystic Graafian follicles; the estrogen-treated ovaries were small and externally smooth but small Graafian follicles were present internally. Graafian and growing follicle cell counts were not significantly different (P > 0.05) among the 2 treatments and control. J. WILDL. MANAGE. 41(4):731-735 The U.S. National Park Service has funded research for the development of a reproductive inhibitor to control the whitetailed deer populations within certain national parks. Previously, synthetic estrogens and progestins have been administered orally to female deer with little success (Harder and Peterle 1974, Matschke 1976a,b, 1977). We therefore sought an alternate method of control, the Silastic implant. Fertility control in animals using Silastic implants was first reported by Dziuk and Cook (1966). They placed tube-type implants subcutaneously in normally cycling ewes and the incidence of estrus was reduced during a 34-day observation period. Estrus was resumed promptly in a majority of ewes upon removal of the device. Fertility control is a result of the diffusion of the drug through the wall of the implant, dissolution of the drug into body fluids, and movement to the target organs. The implant system is more effective than oral administration and more practical than daily subcutaneous injection. There is less accumulation of drugs and metabolites in many tissues than in oral administration. Also, the implan may act as an artificial gland, with a designed release rate near the biological requir ment (Kincl and Rudel 1971). The objectives of this study were to determine the antifertility efficacy of tube-type Silastic implants containing either a synthetic estrogen or progestin, surgically inserted in female white-tailed deer, and to obtain efficacy data which would support a registration application with the Environmental Protection Agency. I thank Dr. Lowell Macy of Abbott Laboratories for furnishing the implants and analyzing the residue.