Zoo Biol. 2026 Mar 20. doi: 10.1002/zoo.70064. Online ahead of print.
ABSTRACT
Musth, a hormonally driven state characterized by increased testosterone, aggression, and physiological changes, poses significant management challenges for male Asian elephants (Elephas maximus) in zoos. Immunological castration, a nonsurgical method using anti-GnRH immunotherapeutic (Improvest®), offers a promising tool to suppress musth. This case study documents the behavioral and physiological effects of immunological castration in a 54-year-old male Asian elephant at the Oklahoma City Zoo with chronic musth-related welfare concerns. In June 2024, the elephant received a primary dose of Improvest® followed by four monthly boosters. Behavioral observations, animal care records, and fecal androgen metabolite (FAM) concentrations were monitored from January 2024 through the elephant’s humane euthanasia due to unrelated degenerative joint disease in January 2025. Segmented regression analyses revealed that FAM concentrations and visible musth signs declined within 7 weeks of the first dose of Improvest®. Aggression also decreased significantly following an inflection point around this time. Even though changes in stereotypy, feeding, and recumbency were not statistically significant, some trended toward improved welfare. Notably, active spermatogenesis was observed at necropsy, suggesting that the effects of Improvest® may require longer to fully manifest or may be partially reversible. Although limited by its opportunistic, single-subject design and shortened study period, this case contributes valuable insight into the real-world application of immunological castration in geriatric zoo elephants. Immunological castration may serve as a useful strategy for male elephants with musth-associated health risks, especially those no longer intended for breeding. Continued longitudinal studies are needed to evaluate long-term efficacy, reversibility, and animal-specific responses to Improvest.
PMID:41859869 | DOI:10.1002/zoo.70064
