CHARACTERIZATION OF GOITER IN CAPTIVE EUROPEAN EASTERN BONGO (TRAGELAPHUS EURYCERUS ISAACI) AND ITS IMPACT ON REPRODUCTIVE HEALTH AND BODY CONDITION.

Goiter or thyroid enlargement has been frequently reported at postmortem examination in Eastern bongos (Tragelaphus eurycerus isaaci). It has been hypothesized that associated thyroid hormone disturbance may be a cause of poor reproductive performance in captive bongos, but thyroid histology or hormone analysis are rarely described. Thyroid glands from 39 individuals within the European captive population were examined grossly, with goiter observed in 64.1% (n = 25) of individuals, of which 96.0% (24/25) had multinodular lesions. Older animals were significantly more likely to develop goiter (P = 0.004), with goiter present in individuals from 6 yrs of age. There was no correlation between the presence of goiter and reproductive success or body condition. Thyroid glands from 16 bongos were examined histologically by a board-certified veterinary pathologist. Histologic lesions were identified in all 16 samples and included giant colloid follicles (100.0%), interstitial fibrosis (93.8%), hyperplastic collapsed follicles (75.0%), papillary fronds (62.5%), inflammation (25.0%), and mineralization (12.5%). No neoplasia was found. Multinodular colloid goiter appears to be the most common thyroid lesion within the European Eastern bongo population. Serum samples collected within 30 d prior to death were available for 25/39 animals, both with and without goiter. Total triiodothyronine (tT3), free triiodothyronine (fT3) and total thyroxine (tT4) concentrations were validated and analyzed by competitive inhibition enzyme immunoassay using bovine ELISA kits. No thyroid hormone levels correlated to goiter presence. Findings suggest that although highly prevalent, colloid goiter is euthyroid and does not impact on reproductive success or body condition in Eastern bongos. The cause of goiter in this species remains unknown.