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 less than .01) in lambs fed ZnMet because of a tendency for lower urinary Zn excretion (P less than .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 less than .10) and 24 h (P less than .05) postdosing in lambs given ZnMet. Thirty-six Hereford x 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 less than .05) gain and feed/gain during the first 56 d, but not for the entire 126-d study.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence is reviewed that indicates Ni is an essential element for the chick, rat, pig, sheep and goat. Although a number of possible functions for Ni have been proposed based on in vitro and in vivo studies, the physiological role of Ni in the mammalian or avian system is presently unknown. Rumen bacterial urease has been shown to be a Ni-dependent enzyme and Ni is a component of factor F430 present in methanogenic bacteria. Nickel can interact or influence the metabolism of a number of minerals. Interactions of Ni and Fe, Zn and Cu are discussed. The requirement for Ni is low (50 to 60 ppb) in chicks fed semipurified diets. Insufficient data are available to estimate the Ni requirement of swine. In ruminants, the Ni requirement appears to be higher than that for other animal species. Nickel supplementation to practical diets has increased gain, feed efficiency and ruminal urease activity in ruminants, but performance results have been inconsistent. Level of crude protein and urea are two factors that influence ruminant responses to dietary Ni. The greatest responses have been observed in ruminants fed low protein diets. Little is known concerning levels, forms and bioavailability of Ni in different feedstuffs. Nickel is homeostatically controlled in the animal's body and high levels of Ni are required to cause toxicity.

Studies were conducted to determine the effects of lysocellin on growth performance and metabolism of steers fed forage-based diets. Treatments in all experiments consisted of 1) control, 2) 100 mg lysocellin/d, 3) 200 mg lysocellin/d and 4) 200 mg monensin/d. In each of two 90-d performance studies, 24 Hereford steers were individually fed greenchop (fungus-free tall fescue and Coastal and Tifton-44 bermudagrass) ad libitum and .91 kg/d of a corn-trace mineral salt supplement. In Exp. 1, tall fescue was fed from d 1 to 45 and bermudagrass from d 46 to 90. Bermudagrass was offered during d 1 to 45 and tall fescue during d 46 to 90 in Exp. 2. Lysocellin improved gain (Exp. 1, P less than .01) and feed conversion (Exp. 1 and 2 combined, P less than .05), decreased total VFA concentrations (P less than .05), increased molar proportions of propionate, isobutyrate and isovalerate (P less than .01), decreased molar proportions of acetate and butyrate (P less than .01) and lowered acetate:propionate (P less than .01). Two metabolism studies involving a total of 16 Hereford steers were conducted. Steers were fed tall fescue greenchop and .91 kg/d supplement for a 34-d adjustment period followed by a 5-d total collection period. Lysocellin increased N digestibility (P less than .01) and N retention (P less than .06) but did not (P greater than .05) affect DM, NDF or ADF digestibility. Data indicate that lysocellin results in major alterations in ruminal fermentation and can increase growth performance and N retention in steers fed forage-based diets.

Studies were conducted to determine the effects of lysocellin and monensin on mineral metabolism of steers fed forage-based diets. In each study treatments consisted of 1) control, 2) 100 mg lysocellin/d, 3) 200 mg lysocellin/d and 4) 200 mg monensin/d. Twenty-four growing Hereford steers were used in each of two experiments to evaluate the effects of ionophore feeding on plasma and ruminal soluble mineral concentrations. Steers were fed individually greenchop (tall fescue and bermudagrass) ad libitum and .91 kg/d of a corn-trace mineral salt-ionophore supplement. Plasma and ruminal fluid samples were obtained on d 28 and 84 in both studies. Ruminal concentrations of soluble phosphorus (P) and iron (Fe) were higher (P less than .05), whereas soluble manganese (Mn) was lower (P less than .01), in steers fed lysocellin than in controls. Steers fed lysocellin had higher (P less than .05) plasma magnesium (Mg) concentrations than control steers. Plasma and ruminal soluble mineral concentrations generally were similar for the monensin and 200 mg lysocellin treatments. Two additional studies were conducted to determine the effects of lysocellin and monensin on macromineral apparent absorption and retention in steers fed tall fescue greenchop. Steers were adjusted to their diets for 28 d and then placed in metabolism crates for a 6-d acclimation followed by a 5-d collection of urine and feces. Percent apparent absorption of calcium (Ca), potassium (K), Mg and P was higher (P less than .05), whereas sodium (Na) absorption was lower (P less than .05), in steers fed lysocellin than in controls. Mineral absorption was similar in steers fed 200 mg lysocellin or monensin. Calcium (P less than .05) and K (P less than .10) retention (percent of intake) was increased by ionophore feeding. Results indicate that lysocellin and monensin alter apparent absorption and retention of certain minerals in steers fed forage-based diets.

Twenty-four Hereford steers averaging 228 kg initially were used to evaluate four levels of lysocellin (0, 11, 22 and 33 mg/kg diet) when individually fed a corn silage-based diet. Gains were similar for all lysocellin levels over the 112-d study. As lysocellin level increased, there was a linear decrease in dry matter intake and an improvement in feed conversion (P less than .05). Feed to gain ratios were 6.27, 6.14, 5.67 and 5.59 for the 0, 11, 22 and 33 mg/kg of lysocellin treatments, respectively. Molar proportion of acetate was lower (P less than .05) and propionate was higher (P less than .05) for steers fed lysocellin than for controls at d 84. Ruminal fluid concentrations of soluble Cu and Zn were higher (P less than .05) in steers fed lysocellin at 28 and 84 d and increased as lysocellin level increased. Plasma Zn was lower (P less than .05) at both 28 and 84 d in steers fed lysocellin, whereas plasma Cu concentrations were similar for controls and for those fed lysocellin. Both ruminal fluid soluble P and plasma P concentrations were higher (P less than .05) in steers fed lysocellin than in controls at d 84. These results are interpreted to indicate that feed conversion of growing cattle is improved by lysocellin and that metabolism of certain minerals is affected by this ionophore.