ZINC REPLETION WITH ORGANIC OR INORGANIC FORMS OF ZINC AND PROTEIN-TURNOVER IN MARGINALLY ZINC-DEFICIENT CALVES

We conducted two experiments using marginally Zn-deficient (-Zn) calve s to determine which supplemental chemical form of Zn would most rapid ly reverse certain Zn deficiency signs and to determine whether a chan ge in protein turnover had occurred in Zn deficiency. In Exp. 1, 40 cr ossbred beef heifers were allocated by BW to four groups. The control group received 23 mg Zn/kg diet DM from ZnSO4 supplemented to the -Zn diet (17 mg Zn/kg diet DM). The three other groups received the -Zn di et. After 21 d, based an a decreased (P < .05) feed efficiency, they w ere deemed -Zn. Cell-mediated immune (CMI) response to phytohemaggluti nin (PHA) was reduced (P < .05)but plasma and liver Zn were unaffected in the -Zn calves. Zinc was repleted by feeding iso-Zn amounts (23 mg Zn/kg diet DM) from Zn lysine, Zn methionine, or ZnSO4. At 8 h after injection of PHA, control CMI response values were similar to Zn Methi onine, and Zn lysine was lower (P < .05). In Exp. 2, 10 Holstein steer s were allocated by BW to two groups. One group received the -Zn diet, and the other received the +Zn diet. Urine collections were obtained from both groups of calves when the -Zn calves showed a decrease (P < .05) in feed efficiency relative to the controls and when they were re pleted with 23 mg Zn/kg diet DM from ZnSO4 and their feed efficiency h ad returned to that of the controls. Urinary 3-methylhistidine indicat ed that -Zn calves had less (P < .05) daily protein degradation than t he controls. Refeeding Zn to the -Zn group did not change BW or daily protein degradation. Results indicated that a marginal Zn deficiency d ecreased fractional accretion rate, increased (P < .05) mine excretion , and tended to increase (P < .19) Na and decrease (P < .12) K concent rations in the mine.