Comparative endocrinology of testicular, adrenal and thyroid function in captive Asian and African elephant bulls

• Published in: General and comparative endocrinology 2007-04, Vol.151 (2), p.153-162
• Main Authors: Brown, Janine L, Somerville, Malia, Riddle, Heidi S, Keele, Mike, Duer, Connie K, Freeman, Elizabeth W
• Format: Article
• Language: English
• Subjects: Adrenal Glands - physiology; Africa; African elephant; Aging - blood; Animals; Asia; Asian elephant; Bulls; Cortisol; Elephants - blood; Endocrinology & Metabolism; Hormones; Hydrocortisone - blood; Male; Musth; Seasons; Testis - physiology; Testosterone; Testosterone - blood; Thyroid Gland - physiology; Thyroid hormones; Thyroid Hormones - blood; Thyrotropin - blood; TSH
• ISSN: 0016-6480; 1095-6840
• DOI: 10.1016/j.ygcen.2007.01.006

Abstract Concentrations of serum testosterone, cortisol, thyroxine (free and total T4), triiodothyronine (free and total T3) and thyroid stimulating hormone (TSH) were measured to assess adrenal and thyroid function as they relate to testicular activity and musth in captive elephants. Blood samples were collected approximately weekly from Asian ( n = 8) and African ( n = 12) bulls at seven facilities for periods of 4 months to 9.5 years. Age ranges at study onset were 8–50 years for Asian and 10–21 years for African elephants. Based on keeper logs, seven Asian and three African bulls exhibited behavioral and/or physical (temporal gland secretion, TGS, or urine dribbling, UD) signs of musth, which lasted 2.8 ± 2.5 months in duration. Serum testosterone was elevated during musth, with concentrations often exceeding 100 ng/ml. Patterns of testosterone secretion and musth varied among bulls with no evidence of seasonality ( P > 0.05). Only three bulls at one facility exhibited classic, well-defined yearly musth cycles. Others exhibited more irregular cycles, with musth symptoms often occurring more than once a year. A number of bulls (1 Asian, 9 African) had consistently low testosterone ( 0.05). For the three bulls that exhibited yearly musth cycles, TSH was positively correlated (range, r = 0.22–0.28; P < 0.05) and thyroid hormones (T3, T4) were negatively correlated (range, r = −0.25 to −0.47; P < 0.05) to testosterone secretion. In the remaining bulls, there were no clear relationships between thyroid activity and musth status. Overall mean testosterone and cortisol concentrations increased with age for all bulls combined, whereas thyroid activity declined. In summary, a number of bulls did not exhibit musth despite being of adequate physical maturity. Cortisol and testosterone were correlated in most bulls exhibiting musth, indicating a possible role for the adrenal gland in modulating or facilitating downstream responses. Data were generally inconclusive as to a role for thyroid hormones in male reproduction, but the finding of discrete patterns in bulls