Contraceptive efficacy of 5-year implantation of levonorgestrel in feral female monkeys.

Objective—To evaluate the contraceptive efficacy of 5 year implantation of synthetic progesterone hormone (75 mg of levonorgestrel) in mature female cynomolgus monkeys (Macaca fascicularis), aged 4.40 ± 0.92 years and weighted 3.28 ± 0.79 kg, inhabiting Pranakorn Khiri, Petchaburi Province. Materials and Methods—Forty monkeys were randomly re-captured, anesthetized and weighed after 0 – 5 years of levonorgestrel implantation. The blood samples were collected for serum estradiol and progesterone determinations, and the cervical mucus was collected and examined for the viscosity. Results—We found that levonorgestrel could suppress ovulation by decreasing serum estradiol and progesterone levels (mean ± SD = 28.36 ± 13.42 pg/ml and 0.12 ± 0.05 ng/ml for estradiol and progesterone levels, respectively) during 0 5 year implantation, and increasing the viscosity of cervical mucus (ranging by 0.55 – 1.50 cm) after 0 2 years of levonorgestrel implantation. Besides, the body weight gains were significantly increased (from 0.26 ± 0.15 kg after 0 – 0.5 years of levonorgestrel implantation to 2.60 ± 0.64 kg after 4.6 – 5.0 year implantation; p<0.05) and correlated with the time of implantation (r = 0.742, P<0.05). Conclusion—From this study, it can conclude that levonorgestrel implantation can exhibit the contraceptive efficacy for at least 2 years, and it can also induce a side effect on body weight gains in feral female monkeys. KKU Vet J. 2012;22(2):185-197. http://vmj.kku.ac.th/