Zinc Methionine for Ruminants: Relative Bioavailability of Zinc in Lambs and Effects of Growth and Performance of Growing Heifers

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Abstract
Studies were conducted to evaluate zinc methionine (ZnMet) as a source of Zn for ruminants. Experiment 1 compared the availability of Zn in ZnMet and zinc oxide (ZnO) in lambs fed a semi-purified diet deficient in Zn. Based on growth rate and animal performance, plasma Zn and plasma alkaline phosphatase activity, no differences in Zn availability were detected between the two Zn sources. Apparent absorption of Zn also was similar, but Zn retention was higher (P < .01) in lambs fed ZnMet because of a tendency for lower urinary Zn excretion (P < .19) in this group. Zinc absorption and retention by lambs were similar for the two Zn sources in Exp. 2 when 20 mg Zn/kg was added to an orchardgrass hay-based diet containing 30 mg Zn/kg. In Exp. 3, lambs were dosed orally with 300 mg of Zn as ZnO or ZnMet, and the increase in plasma Zn following dosing was monitored. The increase in plasma Zn above predosing values was similar at 6 h but was higher at 12 (P < .10) and 24 h (P < .05) postdosing in lambs given ZnMet. Thirty-six Hereford × Simmental heifers (271 kg) were used in Exp. 4 to determine the influence of supplementing Zn (25 mg/kg) as ZnO or ZnMet of growth performance and Zn status. Heifers were fed a corn silage-based diet that contained 23.1 mg Zn/kg during the 126-d study. Zinc supplementation to the basal diet increased (P < .05) gain and feed/gain during the first 56 d, but not for the entire 126-d study. Growth performance did not differ (P > .10) between heifers fed ZnO and those receiving ZnMet, but it tended to be higher (P < .19) for the ZnMet treatment. Plasma Zn and alkaline phosphatase were not affected by Zn source. Alkaline phosphatase in plasma was higher in Zn-supplemented heifers at 42 (P < .10) and 112 d (P < .05). Results suggest that Zn present in ZnO and ZnMet is absorbed to a similar extent, but Zn from these two sources appears to be metabolized differently after absorption. Copyright © 1989. American Society of Animal Science . Copyright 1989 by American Society of Animal Science