The effect of zinc methionine or copper lysine on stocker calves grazing oat pastures

Abstract

Fourty eight Hereford and Angus stocker steers (average weight 259.7 kg) were placed in twelve, five acre, pastures (four steers per pasture) planted with oat forage for a 91 d grazing trial to determine the effect of supplementing zinc methionine and copper lysine on performance and serum copper and zinc concentrations. Zinc methionine and copper lysine were provided in a 2 X 2 factorial arrangement of treatments in a free choice mineral supplement. Steers were weighed, blood samples collected, and hip heights and condition scores recorded at the initiation of the grazing period (d 1), at d 42, and at the conclusion of the trial (d 91). A biopsy of liver tissue was also obtained from each steer on d 91. A copper X zinc interaction (P < .0001) resulted in average daily gain (ADG) during the first 42 d of the trial. This interaction occurred due to a 35% increase in ADG when zinc methionine was added alone and a 38% decrease in ADG when both zinc methionine and copper lysine were supplemented into the free choice mineral supplement. When copper lysine was added, there was a trend (P > .05) to increase ADG 22%. Data summarized over the entire 91 d trial tended to maintain the Cu X Zn interaction. This resulted due to a 10.5% increase in ADG when zinc methionine was supplemented alone and a 4% decrease in ADG when zinc methionine was supplemented with copper lysine. Serum copper concentrations at d 42 also experienced these interactions (P < .05) and were marginal in Cu. Serum Zn concentrations were not significantly different at d 1, d 42, nor d 91 and were adequate in Zn. Liver Cu and Zn concentrations were both marginal at d 91.