Effects of Oral Melengestrol Acetate on Reproduction in Captive White-Tailed Deer

Abstract

Captive white-tailed deer (Odocoileus virginianus) of both sexes were given an antiovulatory drug, melengestrol acetate (MGA; 6a-methyl-6-dehydro-16-methylene-17-acetoxyprogesterone), in feed at 0.6 to 1.0 mg per head daily during the October-March breeding season or for up to 12 consecutive months. MGA inhibited reproduction in adult breeding groups without adverse side effects; did not influence subsequent reproduction in such groups; and did not inhibit the growth, sexual maturation, or subsequent fertility of male or female yearlings or fawns. Discontinuation of MGA treatment of mature females in mid-December was followed shortly by ovulation and conception, but treatment during any stage of gestation from about day 1 through day 192 did not interrupt pregnancies, change gestation length, cause stillbirth, or induce parturition difficulty. Feed intake was not significantly influenced by the addition of MGA. Oral MGA would be feasible for regulating reproduction in small confined herds of deer, but seems impractical for application to larger free-ranging populations because antiovulatory effects require daily ingestion. Implanted MGA, other long-term sterilization treatment, or an oral gametocide appears more attractive for managing free-ranging populations. J. WILDL. MANAGE. 43(2):428-436 Wild ungulate populations in national parks pose special problems for management. Some herds appear to be self-regulating (Cole 1971) and some, because of annual migration to areas outside park boundaries, are susceptible to management by public hunting. Because public hunting is prohibited in most parks, alternative management methods are needed. Traditional alternatives to public hunting have serious disadvantages. Methods that increase mortality (poisoning, control shooting) or simulate increased mortality (herding by helicopter, trapping, and transplanting) encourage compensatory reproduction, survival, and immigration. These compensatory responses are reduced when vertebrate populations are regulated with reproductive inhibitors (Davis 1961). Population management by reproductive inhibitors may be more promising for wild ungulates than for the pest species that Davis (1961) referred to because ungulates have a lower biotic potential. This possibility prompted cooperative research by the U.S. Fish and Wildlife Service and National Park Service to develop methods for regulating reproduction in wild ungulates on Park Service lands. The initial studies reported here dealt with white-tailed deer in Mammoth Cave National Park, Mammoth Cave, Kentucky. All promising chemical, mechanical, and surgical techniques were considered. However, many of these require handling the target animals, and 1 of our 1st priorities was an effective treatment for free-ranging animals that cannot be trapped efficiently; therefore, we sought a chemical treatment that is effective orally and acceptable in baits. Treatment of males was not considered be1A contribution of a cooperative project between the National Park Service and the U.S. Fish and Wildlife Service. 2 Present address: Predator Ecology and Behavior Project, U.S. Fish and Wildlife Service, Department of Wildlife Science, Utah State University--UMC 52, Logan, UT 84322. 428 J. Wildl. Manage. 43(2):1979 This content downloaded from 157.55.39.35 on Thu, 01 Sep 2016 04:39:02 UTC All use subject to http://about.jstor.org/terms EFFECTS OF AN ANTIOVULATORY DRUG ON DEER Roughton 429 cause polygamy could negate population control if small numbers of males escaped treatment. Attention was, therefore, concentrated on finding and testing a safe, nonaversive, orally effective reproductive inhibitor for female whitetailed deer. Melengestrol acetate, or MGA3 (6amethyl-6-dehydro-16-methylene-17-acetoxyprogesterone), was the only promising chemical discovered. MGA is a progestational steroid that inhibits estrus and ovulation and is known to have oral activity in ruminants. MGA has been studied in cattle and sheep as a means of synchronizing estrus, improving feed utilization, and stimulating growth (Zimbelman 1963, Zimbelman and Smith 1966a, Young et al. 1969), and has proven to be effective and safe for both sexes in different age classes (Zimbelman et al. 1970, Schul et al. 1970). Treatment of pregnant cows apparently does not affect the dam or fetus (Schul et al. 1970, Chakraborty et al. 1971). We conducted the present study to determine the effects of MGA-treated feed on the current and subsequent fertility and productivity of male and female adult, yearling, and fawn white-tailed deer. I acknowledge the advice and encouragement of P. L. Hegdal and G. H. Matschke and the assistance of L. Childress, M. W. Holden, J. T. Roughton, and S. D. Miller. Special thanks are due the Kentucky Department of Fish and Wildlife Resources and the personnel of Mammoth Cave National Park, particularly C. F. Pinnix, for their cooperation. I also thank the Upjohn Company for donating supplies of MGA-1003 and for analyzing ration samples, and A. H. Jones for her help in preparing the manuscript. This research was largely funded by the National Park Service under RSP MACA-N-