Effects of manganese proteinate or chromium picolinate supplementation on performance, carcass composition and plasma metabolites in broilers reared under thermoneutral or chronic heat stress conditions

A study was conducted to investigate the effects of supplemental chromium picolinate (CrPic) or manganese proteinate (MnPro) on heat-distressed broiler chickens. In a completely randomized design, dietary levels of supplemental Chromium (Cr) at 200 and 400 µg/kg or Manganese (Mn) at 0, 60 and 240 mg/kg were fed under heat stress (HS) or thermoneutral (TN) conditions. Commercial broilers were reared in brooder pens and fed the experimental diets from day one to 21 and then assigned the same dietary treatments in one of two environmentally controlled chambers. Each treatment consisted of 4 replicates 5 chicks in each chamber. The first chamber was maintained at 23.9 °C, while birds in the second chamber were exposed to 8 h of 23.9 °C, 4h of 23.9 to 35 °C, 4h of 35 °C and 8h of 35 to 23.9 °C. Growth and feed intake were determined weekly. At 7 weeks of age six birds per treatment were weighed and slaughtered for determination of carcass yield and composition. Blood samples were collected from the remaining birds for determination of plasma metabolite and hormone concentrations. Dietary Cr supplementation increased total gain (p<0.01) and feed efficiency (p<0.02). Increased Feed intake resulted from High Mn (p<0.01) or no Mn (p<0.05) supplementation. Heat stress conditions reduced gain and feed intake (p<0.001) and increased feed efficiency (p<0.04). Plasma concentrations of insulin (I) was lower (p<0.01) in birds supplemented high Mn but, glucagon (G), I:G ratio, and glucose were not affected (p>0.05) by dietary treatment regimen. Heat stress lowered insulin (p<0.004), increased glucagon (p<0.002) and lowered I:G ratio (p<0.02). Serum concentrations of non- esterified fatty acids was lower in high Mn supplemented group but, triglycerides (TG), total cholesterol (CHOL), high-density lipoprotein (HDL) cholesterol and HDL: CHOL ratio were not affected (p>0.05) by dietary treatment. Heat stress birds receiving no Mn supplementation had lower HDL: CHOL ratio (p<0.02) while HS reduced serum TG concentrations (p<0.04). Yield of back portions (p<0.0004) and ether extract of thigh portions (p<0.02) were lowered by Cr supplementation. In addition, Cr supplementation under HS resulted in increased crude protein in thigh portions. Heat stress conditions decreased abdominal fat (p<0.001), and increased percentage yield of carcass (p<0.002), breast (p<0.04) and leg (p<0.002). High Mn supplementation resulted in higher AFP under conditions of HS but lower AFP in TN environment (p<0.02). This was the reverse response to the control group. Based on these results CrPic supplementation under HS or TN improves live performance and carcass composition. Further, MnPro supplementation appears to be beneficial but additional studies are required.