Effects of Chromium Yeast on Performance, Insulin Activity, and Lipid Metabolism in Lambs Fed Different Dietary Protein Levels

This experiment was conducted to study the effects of chromium (Cr), dietary crude protein (CP) level and potential interactions between these two factors on growth rate and carcass response, insulin activity and lipid metabolism in lambs. Forty-eight, 9-week-old weaned lambs (Dorper$\times$Small-tail Han sheep, mean initial body weight = $22.96kg{\pm}2.60kg$) were used in a $2{\times}3$ factorial arrangement of supplemental Cr (0 ppb, Cr0; 400 ppb, Cr1; or 800 ppb, Cr2 from chromium yeast) and CP levels (157 g/d to 171 g/d for each animal, LP; or 189 g/d to 209 g/d for each animal, HP). Growth data and blood samples were collected at the beginning and end of the feed trial, after which the lambs were killed. Both Cr additive groups and the HP group increased final weight and average daily gain, especially the Cr1 and HP group (p<0.01). HP increased pelvic fat weight (p<0.05), fat thickness of the 10th rib (p<0.05), longissimus muscle area (p<0.01) and rate of deposition of intramuscular fat (p<0.01). Supplemental Cr decreased the rate of deposition of intramuscular fat (p<0.05). Fasting insulin level and the ratio of insulin to glucose were lower with Cr1 than other groups, but with no significant difference. Glucose concentration was not affected by any treatment. Nonesterified fatty acids increased in the Cr1 (p<0.05) and HP (p<0.05) conditions and there was a significant $Cr{\times}CP$ interaction (p<0.05). Cr1 decreased triglycerides (p<0.05) and total cholesterol (p = 0.151) and HP increased high-density lipoprotein cholesterol (p<0.05). Cr1 decreased lipoprotein lipase activity in subcutaneous adipose tissue (aLPL, p<0.05) and the ratio of aLPL to lipoprotein lipase activity in skeletal muscle (mLPL, p = 0.079). mLPL and hepatic lipase (hHL) were not affected by any treatment. In the present study, Cr had limited effects on growth rate and carcass response, whereas Cr and CP had some notable effects on plasma metabolites and enzyme activities. Cr has a potential effect on energy modulation between lipid and muscle tissue. In addition, few $Cr{\times}CP$ interactions were observed.