Thyroid hormone levels in response to dietary supplementation of garlic (Allium sativum) in chicken

The study was conducted to investigate the role of garlic supplementation in feed on the thyroid hormones. The investigation was carried out on 24 broiler chicks, divided randomly into 3 groups, each group consisting of 8 birds. Group I birds were used as control kept on conventional diet. Group II and III birds were supplemented with garlic at the rate of 1.5% and 3.0% respectively (on dry matter basis) of total feed for a period of 8 weeks. Thyroid hormones viz. tri-iodothyronine (T₃) and thyroxine (T₄) were measured at 4^th, 6^th and 8^th week of age using Radioimmuno Assay (RIA) technique. There was an insignificant decrease in T₃ and T₄ hormone levels due to garlic supplementation in feed, except at 8^th week of age the garlic supplementation showed a significant decrease in T₄ level as compared to the control birds. But with the advancement of age there was a significant decrease in T₄ level in control as well as garlic supplemented groups at 8^th week of age in comparison to 4^th and 6^th week of age. These findings suggest a decrease in T₄ level at 8^th week of age which is sensitive to garlic supplementation in feed that may be a function of age related metabolic change in the chicken.