The present study examined ultrastructure of the thyroid gland of adult West African Dwarf (WAD) goat in order to further understand the ultrastructural morphology and some of the changes in the components of the thyroid gland in goat with age. Thyroids glands obtained from fifteen adult WAD goats of different ages and sexes slaughtered at the local abattoirs were used in this study. Electron microscopic techniques were used to study the fixed tissue with emphasis on the follicular and parafollicular cells. The results showed that the ultrastructure is generally similar to that of some domestic animals. Follicular cells were cuboidal in young adult goats thyroids but were flattened in older goat thyroids of 5–7 years. These cells remarkably showed highly dilated cisternae of rough endoplasmic reticulum which decreased in frequency the older goats. Microvilli were short and sparse on the follicular cells and the number decreased in the older goats. Different sizes of apical vesicles of varying electron density were encountered that included colloid droplets, secretory vesicles and lysosome-like bodies and the appearance of these vesicles changed with age. Parafollicular cells were encountered in the basal position between follicular cells in all thyroids examined. Numerous dense cytoplasmic granules were observed and they were not apparently different from that described in several mammals.

KEY WORDS: Ultrastructure; Thyroid gland; Dwarf goat.