Influence of dietary supplemental chromium and magnesium on performance and metabolic parameters of laying hens subjected to heat stress

To determine the effects of adding supplemental Mg and Cr to diets on performance, egg quality, blood parameters and enzyme activity of laying hens subjected to heat stress, a total of 324 laying hens were used and based on a 3 x 3 factorial, nine diets, six replicates, including basal diet with Mg (0, 300 and 600 mg kg(-1) from Mg oxide) and three levels of Cr (0, 400, 800 mu g kg(-1) from Cr methionine) were fed to the experimental birds. The temperature was increased gradually up to 31 degrees C for 5 weeks. Feed conversation ratio and egg mass improved in the birds fed either 300 or 600 mg kg-1 Mg compared to those fed the basal diet (P < 0.05). During the heat stress, birds fed the diets included 300 or 600 mg kg(-1) Mg produced eggs with higher shell thickness. Dietary supplemental Mg and Cr separately decreased blood uric acid in laying hens during heat stress (P < 0.05). It can be concluded that diet supplementation by Mg could have beneficial effects on feed conversation ratio, shell thickness and serum uric acid, whereas diet supplementation by Cr decreased serum glucose, total cholesterol, triglycerides and uric acid of laying hens under heat stress condition.