LEVONORGESTREL IMPLANTS AS A CONTRACEPTIVE IN CAPTIVE WHITE-TAILED DEER

Silastic implants containing levonorgestrel (LNG) were evaluated as a contraceptive in captive white-tailed deer (Odocoileus virginianus). S ix adult females and six female fawns received either six or nine impl ants in autumn. Each implant contained 36 mg of LNG. Blood was analyze d by radioimmunoassay to determine LNG release profile for 5 mo post-i mplantation. Serum LNG concentrations rose significantly (P = 0.0005) 3 days post-implantation, leveled off after 7 days, and did not change (P = 0.5913) during the remaining 5 mo. Mean (+/-SE) LNG concentratio ns for all months were higher (P = 0.0377) in adult and fawn females i mplanted with nine versus six rods (138.1 +/- 14.4 versus 56.7 +/- 12. 3 pg/ml, respectively). Serum LNG levels did not differ between adults and fawns. Five of the six implanted adult females had normal estrous cyclicity; three of these five adult females became pregnant in the f irst year. Four implanted females (two yearlings and two adults) were monitored during a second year, and housed with a fertile buck; three of them became pregnant. We do not recommend the use of LNG in deer.