Copper Super-Dosing Improves Performance of Heat-Stressed Broiler Chickens through Modulation of Expression of Proinflammatory Cytokine Genes

Abstract

Continuous exposure to high ambient temperatures brings about a number of oxidative damages in chickens. Copper (Cu), an active component of a number of antioxidative defence components, should arrest these changes to take place although that may not be possible under the standard dosing regimen followed by the industry. To ascertain the optimum dose response that may be beneficial in sustaining the performance of chickens under heat stress (HS), broiler chickens (n = 400) were exposed to high ambient temperature (between 27.2°C and 35.3°C) during 1–35 d. Copper (Cu) as Cu proteinate (Cu-P) at concentrations of 37.5, 75, 112.5, and 150 mg/kg was supplemented to the diet. The negative control (NC) diet did not contain any supplemental Cu. Increasing dietary Cu improved ( $P<0.001$ ) body weight, feed intake, and conversion ratio. Serum concentrations of total cholesterol at 21 d ( $P=0.009$ ), HDL cholesterol at 35 d ( $P=0.008$ ), LDL cholesterol at 21 d ( $P=0.015$ ), and triacylglycerol at both 21 d ( $P=0.033$ ) and 35 d ( $P=0.001$ ) decreased as Cu in the diet increased. As Cu in the diet increased, hemoglobin increased ( $P=0.003$ ) at 21 d, and the heterophil to lymphocyte ratio decreased both at 21 d ( $P=0.047$ ) and 35 d ( $P=0.001$ ). Superoxide dismutase and glutathione peroxidase activities increased when dietary Cu increased to 150 mg/kg ( $P<0.01$ ). Liver Cu at 35 d increased linearly with the dose of Cu in the diet ( $P=0.0001$ ). Selected bacteria were enumerated in the digesta to ascertain if Cu super-dosing affected their population in any way in the absence of any enteric challenge. Escherichia coli and total Salmonella numbers decreased ( $P=0.0001$ ), and total Lactobacillus increased ( $P=0.0001$ ) proportionately with dietary Cu. Interleukin-6 and tumour necrosis factor-α gene expression increased linearly ( $P=0.0001$ ) as Cu in the diet increased though the response plateaued at 112.5 mg/kg. It was concluded from the present experiment that during conditions of impending HS, dietary supplementation of 112.5 to 150 mg Cu/kg diet as Cu-P may be a novel strategy to alleviate the negative effects of HS without involving any apparent risk of Cu toxicity.