effect of thyroid activity modulation on some histological and biochemical aspects in broiler chicks

an experiment was conducted to investigate the effect of thyroid gland activity modulation (hyper or hypothyroidism) on energy utilization in broiler chickens. two hundred and forty one-day-old cobb broiler chicks were distributed into three dietary metabolizable energy (me) treatment groups (80 chicks each). the control group (e0) was fed basal diet (3150 kcal/kg diet), the second group (e1) was fed low me diet (3000, kcal/kg diet) with different thyroidal treatments and the third group (e2) was fed very low me diet (2850 kcal/kg diet) with thyroidal treatments. thyroidal treatments were applied at the beginning of the 2nd week, where (t0) was a control treatment; two hyperthyroidism groups induced by administration of eltroxin (t1) or calcium iodide (t2), and hypothyroidism group induced by carbimazole administration (t3). results showed that plasma thyroidal hormones (t3, t4) concentrations and their ratio t3 / t4 showed considerable changes related to thyroidal treatments. plasma glucagon (g) level was significantly increased while insulin (i) level and i / g ratio were significantly decreased as affected by lowenergy diets. carbimazole administration group had the lowest plasma insulin level and i / g ratio compared to other treatments. moreover, calcium iodide significantly increased adenosine triphosphate (atp), total adenylate(ta) and phosphatepotential(pp) while carbimazole significantly decreased adenosine diphosphate (adp) and adenosine monophosphate (amp). histological examination of thyroid gland sections reflect the beneficial use of calcium iodide (cai) as a safe additive without hazards effect on thyroid gland histology. results suggested that calcium iodide could be used to maximize the utilization of lowenergy diets, via its modulating action of thyroid gland activity.