Histology of the Thyroid Gland in Large White Yorkshire Pigs Reared at Low and High Altitudes of Kerala, India
Résumé
The histological and ultrastructural studies were carried out on thyroid samples (n = 24) collected from ten–month-old Large White Yorkshire pigs of either sex reared in low altitude and high altitude of Kerala. Histologically, the gland enclosed spherical or oval thyroid follicles of various sizes. Small-sized follicles were predominantly in the peripheral zone of the gland. The staining intensity of the colloid within the follicles varied from acidophilic to basophilic. A single layer of low cuboidal cells lined the follicles. Predominance of basophilic colloid, vacuoles at the periphery of the colloid, and taller lining cells indicated an active follicle. Active follicles were more numerous in the low-altitude male and female groups than in the corresponding high-altitude groups. The larger, lightly stained Parafollicular cells were present either singly or in groups at intrafollicular, parafollicular, or interfollicular pattern. The serum T3 and T4 hormones were significantly higher in the low-altitude male group than in the corresponding high-altitude group. In female animals, the serum T4 hormone levels recorded significantly higher values in the low-altitude group than in the high-altitude group. The average serum T4 levels in males were significantly higher than in females at both altitudes. However, the T3 values did not differ significantly between male and female groups at both altitudes. The recorded variation in T3 and T4 hormones may be attributed to the higher ambient temperature at the low altitude than at the high altitude.