SUFFICIENCY OF CU AND ZN IN BARLEY, FORAGE, AND CORN SILAGE RATIONS AS MEASURED BY RESPONSE TO SUPPLEMENTS BY BEEF CATTLE

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Abstract
Beef heifers of 232 and 205 kg average beginning weight, fed individually in a barn in two separate trials, were assigned at random to the following treatments: (A) basic barley–hay ration containing 3–1 ppm Cu and 25–32 ppm Zn; (B) basic ration supplemented to 11–12 ppm Cu; (C) basic ration supplemented to 63–66 ppm Zn. The Cu-supplemented ration resulted in an increased amount of Cu in the liver (P < 0.01). The Zn-supplemented ration resulted in a decreased amount of Cu in the liver in trial 1 (P < 0.05) but did not affect the level of Zn either in the liver or in the hair. No difference was found in average daily gain, feed consumption, efficiency of gain, or dressing percent of the heifers. It was shown that under a full-feed regime for 134 and 151 days, young animals (heifers) with Cu levels in the liver of 100 ppm or more on a dry weight basis can maintain normal metabolic balance when their ration is less than 4 ppm Cu and 33 ppm Zn. Barley and forage grown on Grey Wooded soil of the Peace River area, even though analytically low in Cu and Zn, are sufficient for heifers on full feed. In a third trial, beef steers were fed for 112 days on corn silage fortified with urea. Copper glycinate injections showed no effect on gain, although final concentrations of Cu in the liver were increased from 28 to 133 ppm on a dry weight basis. The corn silage contained 7 ppm Cu and had a Cu/Mo ratio of 6:6. Copper supplementation of corn silage rations is not warranted with this level of copper and a favorable Cu/Mo ratio.

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