Effects of Mineral Source on Growth and Balance in Yearling Horses1

Sixteen Quarter-Horse yearlings were used in a split-plot designed experiment to evaluate the response of growth and mineral balance to trace mineral source. Horses were blocked by sex and BW and randomly assigned to either an inorganic (ING) or organic (ORG) treatment. Diets were formulated to contain supplemental levels of Zn, Cu, Mn, and Co at four times NRC (1989) recommendations for yearlings in rapid growth. Diets were fed at 2% of estimated final BW and consisted of a pelleted concentrate, Marshall ryegrass hay, and alfalfa cubes fed in a 50:30:20 ratio, respectively. Three 72-h total fecal and urine collections were conducted on d 7, 30, and 60. Blood was taken on d 1 of each total collection to measure serum mineral (Zn and Cu) concentrations. Although mineral digestibility and balance data were not consistent across periods, significant increases in Cu (Period II) and Co (Periods II and III) digestibility and balance were observed for the ORG treatment. These increases indicate that ORG trace minerals may be more available for absorption as compared with IN sources, although excessive supplementation of trace minerals in the diet may obscure differences because of trace mineral source. Thus, the feeding of ORG trace minerals may improve trace mineral absorption, subsequently improving balance and digestibility.