ABSTRACT. This study was conducted to determine the correlation between reproductive hormones and musth in a male African elephant. Changes in circulating luteinizing hormone (LH), follicle stimulating hormone (FSH), testosterone and immunoreactive (ir-) inhibin and the degree of musth were evaluated for 4 years. LH increased 4 weeks before musth began. The highest concentrations of testosterone and ir-inhibin were observed from April to October. There were positive correlations among testosterone, ir-inhibin and musth behavior. These findings suggested that the surge-like LH in the pre-musth period might stimulate secretion of testosterone and ir-inhibin and thus initiate the musth behavior. This study also suggested that the high LH level before musth might be a useful biomarker for the beginning of the musth season.KEY WORDS: African elephant, inhibin, luteinizing hormone, musth, testosterone.J. Vet. Med. Sci. 73(3): 379-383, 2011 Musth is a unique phenomenon that occurs either annually or semiannually in adult male African (Loxodonta africana) [7,16,17] and Asian (Elephas maximus) elephants [5,11]. During musth, male elephants have elevated levels of androgens, especially androstenedione and testosterone [1,6,7,10,15,18,20,21,24]. Musth bulls were reported to have elevated levels of luteinizing hormone (LH) in both African [1] and Asian [15] species. Secretory patterns of follicle stimulating hormone (FSH) and immunoreactive (ir-) inhibin in male elephants have never been reported before. In captivity, both African and Asian bulls in musth exhibit aggression towards their mahouts or handlers [5,10,20], which is extremely dangerous for zoo staff, veterinarians and researchers who manage breeding programs. Thus, our understanding of markers for prediction of musth needs to be improved. The objective of this study was to investigate secretion of reproductive hormones associated with musth characteristics in a male African elephant in Japan.A male African elephant named "Tamao" (Fig. 1A) was studied for 4 years, from 33 to 37 years of age. It was housed at the Tama Zoological Park, Hino City, Tokyo, Japan, together with 4 female African elephants. All elephants were housed outside during the daytime (0900 hr-1600 hr) and inside the building at night throughout the year. Blood samples were collected weekly between 0800 hr and 0900 hr from an ear vein without anesthesia. The samples were centrifuged, and sera were stored at -20C until hormonal analysis. The appearance of characteristic behavioral and physical changes was recorded daily during the 4-year period. The bull elephant was classified as being in musth when one or a combination of the following behavior and/or physical changes were continuously (for more than 3 days per week) observed: increased aggressive behavior, temporal gland secretion (TGS; Fig. 1B) and urine dribbling (UD; Fig. 1B) as described previously [3]. Since TGS can occur in African bulls under stress or social excitation, TGS was considered as an indicator of musth only if it occurred ...