Besides surgical sterilization, contraceptives for wildlife include hormonal methods, fertility inhibitors such as immunocontraceptives, nicarbazin, VCD (4-vinylcyclohexene diepoxide), triptolide and nicarbazin. Hormonal methods, used in zoo animals and livestock, are based on synthetic hormones which bind to hormone receptors and disrupt reproduction. Those tested as wildlife contraceptives include levonorgestrel and quinestrol. Levonorgestrel implants, originally approved for human contraception, inhibit reproduction by preventing ovulation or fertilization in several marsupials. Combined with another hormone, quinestrol, levonorgestrel has been used as oral contraceptive in many rodent species. Gonadotropin releasing hormone (GnRH) agonists, such as deslorelin, are proteins that mimic GnRH. Delivered as implants, GnRH agonists, inhibit reproduction in cattle, marsupials, felids and wild dogs.

Immunocontraceptive vaccines induce antibodies against proteins or hormones essential for reproduction. GnRH-based immunocontraceptives, used by the pig industry to prevent “boar taint,” generate antibodies to GnRH, thus disrupting the release of sex hormones in males and females. Injectable GnRH-based vaccines induce infertility in deer, wild boar, cats, horses, bison, feral cattle, ground squirrels, prairie dogs, and marsupials. Porcine zona pellucida (PZP)-based immunocontraceptives are used in females to prevent fertilization. Injectable PZP-based vaccines prevented reproduction in several deer species, primates, seals, elephants, bears, and marsupials. VCD and triptolide, orally delivered, impair ovarian and sperm function in rats. Nicarbazin, employed to prevent coccidiosis in chickens, also reduces the number of eggs laid and hatched and it is used as an oral contraceptive for pigeons.