Influence of chromium tripicolinate on growth and glucose metabolism in yearling horses

Thoroughbred and Quarter Horse yearlings (n = 24; 335 +/- 7 d of age) were used in a 112-d feeding trial to determine whether chromium (Cr) supplement ation would alter growth, development, and energy metabolism of growing hor ses on high-concentrate diets. The horses were assigned at random within br eed and gender subgroups to one of four treatment groups: A) basal concentr ate; B) basal plus 175 mu g of Cr/kg concentrate; C) basal plus 350 mu g of Cr/kg concentrate; and D) basal plus 700 mu g of Cr/kg concentrate. Chromi um was provided via Cr tripicolinate (Prince Agri Products, Quincy, IL). Th e horses were weighed, measured for withers and hip height, heart girth, an d body length and underwent ultrasound evaluation for croup fat thickness. The concentrate was fed for ad libitum consumption for two, 1.5-hr feeding periods daily. Coastal bermudagrass (Cynodon dactylon) hay was group-fed (s ix animals/group) at 1% of BW daily. Feed intake was 60% concentrate and 40 % hay, resulting in a supplemental Cr intake of 0, 105, 210, and 420 mu g/k g diet for groups A, B, C, and D, respectively. Colts consumed more concent rate and total feed than did fillies (P < .05), but no dietary effect on fe ed intake was detected. Colts weighed more than fillies at the completion o f the experiment (P = .0754), but no dietary effects on weight, body measur ements, or croup fat were detected. An i.v. glucose tolerance test (.2 g of glucose/kg BW) and an i.v. insulin sensitivity test (.1 IU of insulin/kg B W) mere conducted on each animal during the third 28-d period of the experi ment. Plasma glucose peaked immediately following injection and decreased m ore rapidly in animals consuming the high-Cr diet than in those consuming t he control diet (P < .01). Mean glucose fractional turnover rate values inc reased (P = .0369) and mean half-life of glucose decreased (P = .0634) in r esponse to the high Cr supplementation. Plasma glucose depletions in animal s fed the other two diets were between and not different from (P > .10) the depletions in control animals or in those fed high-Cr diets. No difference in insulin sensitivity was detected (P > .10). Results indicate that Cr tr ipicolinate supplementation of yearling horses increases the rate at which glucose is metabolized and may lower the plasma glucose concentration. No e ffect of Cr supplementation on development of the animals was detected.