MULTISYSTEM EFFECTS OF MUSTH ON IMMUNE FUNCTION AND PHYSIOLOGY OF ASIAN ELEPHANTS (ELEPHAS MAXIMUS)

Understanding how reproductive states influence immune function is critical for advancing the care of managed wildlife species. Male Asian elephants (Elephas maximus) undergo musth, a periodic reproductive state characterized by elevated testosterone and behavioral changes, which may impose physiological costs. The effects of musth on immune function and systemic physiology remain poorly understood. This study evaluated multisystem biomarkers to characterize physiological changes associated with musth in two zoo-housed male Asian elephants over a five-year period. We analyzed hematologic parameters, serum amyloid A (SAA), and cortisol concentrations from blood samples collected before, during, and after musth episodes. Linear mixed-effects models revealed that musth was associated with significant increases in white blood cell and platelet counts, SAA, cortisol, and heterophil percentage, and decreases in red blood cell count, hematocrit, and eosinophil percentage. Principal component analysis indicated that musth samples clustered distinctly from non-musth samples, reflecting coordinated shifts across hematologic, inflammatory, and endocrine systems. The magnitude of physiological deviation from baseline peaked after 72 days of musth progression and declined over time, suggesting dynamic physiological adjustment. These findings support the hypothesis that musth incurs measurable physiological costs, characterized by immune activation and stress axis engagement. Clinically, our results highlight the importance of reproductive state when interpreting health biomarkers in male elephants and suggest that early musth may represent a period of elevated health risk. Broader application of integrative, multi-biomarker approaches may enhance clinical monitoring and improve welfare outcomes for elephants and other large mammals undergoing energetically demanding life-history events.