Hyperplastic goitre and mortality in captive-reared black stilts (Himantopus novaezelandiae)

Abstract

AIM: To study the gross, histopathological and clinicopathological findings in cases of hyperplastic goitre in sub-adult captive-reared black stilts following their release on riverbeds in the south Canterbury region of New Zealand.

METHODS: Necropsies were undertaken on the recovered carcasses of 48 black stilts over a 3-year period (1997–1999). The cause of death was determined, and thyroid glands were examined histopathologically and compared with those of free-living pied stilts. Concentrations of triiodothyronine (T₃) and thyroxine (T₄) in the serum of sub-adult and adult stilts were measured before and after iodine supplementation.

RESULTS: The main causes of death of captive-reared black stilts following release were trauma, predation and starvation. An increase in size of the thyroid gland due to follicular hyperplasia and dilation was seen in all birds with intact thyroid glands (n=27). Dysplastic follicular changes such as epithelial desquamation, lipid deposition and haemorrhage were common in a large proportion of individuals with goitre. Dietary supplementation with iodine greatly improved survival rates in sub-adults following release, and significantly increased concentrations of T₃ and T₄ in serum.

CONCLUSIONS: Subclinical goitre due to thyroid hyperplasia and dysplasia was the cause of hypothyroidism and this contributed to the poor survival of released sub-adult black stilts raised in captivity. Iodine supplementation of the diet of captive adults and sub-adults resulted in increased concentrations of T₃ and T₄ in serum and improved survivability.

KEY WORDS:

• Black stilt
• goitre
• iodine deficiency
• thyroid hyperplasia
• thyroxine
• triiodothyronine

Acknowledgements

We are grateful to Mrs P Slack and Mrs P Davey for providing histological sections of the tissues of normal and affected birds, and to members of the Black Stilt (kaki) Recovery Programme for their help with releases of black stilts and for collection of samples. Staff at Ruakura Animal Health Laboratory provided T₃ and T₄ analyses of sera from juvenile birds before and after release. The thyroid analyses project was funded by the New Zealand Department of Conservation Science Fund.