With the rapid development of the poultry industry,scientists around the globe are now focusing on the role of micronutrients in poultry diets to ensure better production.Although micronutrients are required in minute quantities in the poultry diet,they play an important role in improving birds’ health and vigor.Chromium（Cr）is a micronutrient which plays a vital role in animal nutrition and involved in metabolism of carbohydrates,proteins,lipids and nucleic acid.Cr considered as a vital element for animals and birds.Present study was conducted to evaluate the effectiveness and tolerance of chromium propionate in broilers.There were two trials.First trial was conducted to evaluate the effectiveness of chromium propionate（treatment group B-F）.Second trial was conducted to evaluate the tolerance of chromium propionate（treatment group G and H）,while control group was common（group A）.One day old broiler chicks（n=1008）were divided into eight experimental groups each containing 126 chicks,further divided into 7 replicates（18 chicks/replicate）.All birds were offered corn-soybean diets supplemented with varying concentrations of Cr（0,0.10,0.15,0.20,0.25,0.30,0.50 or 5.0 mg/kg named as group 1,2,3,4,5,6,7,and 8,respectively）.The entire study results were grouped into four experiments thus;Experiment 1.Effects of dietary inclusion of chromium propionate on growth performance,intestinal health,immune response and nutrient transporter gene expression in broilersThe intent of this part of study was to evaluate the effect of chromium（Cr）as chromium propionate on growth performance,organ index,immune response,intestinal morphology and nutrient transporter gene expression in broilers.One-day-old broiler chicks（n = 756）were divided into six experimental groups of 126 chicks;each group was further divided into 7 replicates（18 chicks/replicate）.All birds were offered corn-soybean diets supplemented with Cr3+ at 0,0.10,0.15,0.20,0.25 or 0.30 mg/kg.Dietary inclusion of Cr at various levels yielded significantly better growth performance and organ index in birds.Similarly,antibody titre against New-castle disease and avian influenza H5 at various ages was found to be significantly higher in birds that received 0.15 mg/kg Cr in the diet.Significant results with respect to villus height（VH）,crypt depth（CD）and VH:CD were observed in all groups that received Cr in the diet compared to control.Moreover,it was observed that different levels of Cr supplementation of the diet also increased the expression of the nutrient transporter genes SGLT1,GLUT2,r BAT and CAT1 in broilers.The findings of the present study suggest that dietary inclusion of Cr at various levels may have beneficial effects on growth performance,immunity,intestinal morphology and nutrient transporter gene expression in broilers.Supplementation of the diet with Cr3+ at a level of 0.15 mg/kg could yield better performance in broiler production.Experiment 2.Effect of dietary chromium propionate on insulin sensibility,blood profile,serum biochemical markers,antioxidant markers and liver metabolic enzymes expression in broilersThis experiment was conducted to evaluate the effect of（Cr）as chromium propionate on insulin sensibility,blood biochemical properties,serum biochemical properties,antioxidant markers and liver metabolic enzymes expression in broilers reared under normal conditions.One day old broiler chicks（n=756）were divided into six experimental groups each having 126 chicks,further divided into 7 replicates（18 chicks/replicate）.All birds were offered corn-soybean diets supplemented with Cr at 0,0.10,0.15,0.20,0.25 or 0.30 mg/kg.Dietary inclusion of Cr at various levels showed significant effect on serum insulin tolerance.Dietary inclusion of Cr at various levels exhibited significantly better effect on blood and serum biochemical parameters.Addition of 0.30 mg/kg of chromium in the diet significantly increased the expression of liver metabolic enzymes.The addition of chromium propionate in the diet significantly reduced the content of malondialdehyde in serum at 21 days of age.Findings of the pre sent study suggest that dietary inclusion of Cr at various levels could have beneficial effects on insulin sensitivity,blood biochemical properties,serum biochemical properties,antioxidant markers and liver metabolic enzymes expression in broilers.Conclusively,a level of 0.15 mg/kg of Cr could yield better results in broiler production.Experiment 3.Dietary tolerance of chromium propionate supplemented at higher levels in broilersThis study was conducted to evaluate dietary tolerance of chromium propionate supplanted with higher levels in broilers.One day old broiler chicks（n=504）were divided into four experimental groups each having 126 chicks,further divided into 7 replicates（18 chicks/replicate）.All birds were offered corn-soybean diets supplemented with Cr at 0,0.50 or 5.0 mg/kg.Supplementation of Cr did not cause any side effects on broiler growth performance,organ index and intestinal morphology in broilers.The effect of Cr supplementation on antioxidant remained non-significant.Dietary inclusion of Cr at various levels showed no adverse effect on serum insulin levels.Dietary inclusion of Cr at 0.5 and 5 mg/kg showed non-significant results for intestinal morphology however,some better results for nutrient transporter gene expression e.g.SGLT1 in duodenum of broiler and GLUT2 were seen in jejunum and ileum of small intestine.Furthermore,dietary inclusion of Cr did not showed any adverse effect on blood and serum profile.Conclusively,chromium propionate used at 0.5 mg/kg and 5 mg/kg,statically did not showed any adverse effect on the overall performance of birds.However,dietary level 5 mg/kg of chromium propionate could damage liver tissue.Experiment 4.Metabolomics approach on serum of broilers with or without dietary supplementation of chromium propionateSerum is a suitable tool for metabolomics study.Metabolomics approaches provide a comprehensive understanding for the effect of chromium propionate in nutrients metabolism such as amino acids,carbohydrates and lipids metabolism in vitro.Serum sample were taken from broiler,were offered diet with or without supplementation of chromium propionate.The metabolomics analyses revealed 76 differential metabolites between groups with or without Cr supplementation.Further pathway interpretations revealed that 55 metabolites out of 76 showed positive trend from amino acids,carbohydrates and fatty acids,which is an indication of role of chromium propionate in metabolism of different metabolites.It is concluded from the results of the present study that 0.15 mg/kg of chromium propionate supplementation in broiler diet is best to use to improve overall performance and health of broiler birds.While,supplementation of chromium propionate at level 5 mg/kg can be toxic for liver.Furthermore,metabolomics studies indicate that chromium propionate have a role in metabolism of different nutrients.