Effect of Protein Levels and Rumen Protected Glutamine Supplementation on Blood Metabolites, Thyroid Hormones, and Redox Status of Heat Stressed Fattening Lambs

High ambient temperatures have a negative effect on the production and health of animals. Severe heat stress may lead to changes in the secretion of hypothalamus and pituitary gland hormones, which alter hor-monal responses and metabolism. The aim of this study was to determine the effect of protein levels and rumen protected glutamine supplementation on blood metabolites, thyroid hormones concentrations, and redox status of fattening heat stressed lambs. Using sixteen Afshari male lambs (aged 3-4 months) over 45 days, a 2 × 2 factorial were designed to study the effects of two levels of protein (equal and 10% higher than requirement) and glutamine (0.0 and 0.2 g/kg body weight) in four experimental rations. Results showed the glutamine supplementation increased triiodothyronine and thyroxine concentrations; and con-versely decreased aspartate transaminase, non-esterified fatty acids, and cortisol concentrations. Increased protein levels at the beginning of fattening did not affect triiodothyronine, thyroxine, aspartate transami-nase, alanine transaminase, and non-esterified fatty acids concentrations. Interaction of glutamine and pro-tein levels significantly decreased cortisol concentrations. Glutamine supplementation increased levels of superoxide dismutase and glutathione peroxidase, and decreased nitric oxide. The greater protein levels significantly decreased superoxide dismutase and glutathione peroxidase on day 30, total antioxidant status concentration on day 15 and 45, and increased nitric oxide concentration on day 15 of fattening. It can be concluded that glutamine supplementation improves redox status of heat stressed lambs during the fattening period but increase protein levels alone did not have this effect.