EFFECT OF DIETARY POTASSIUM ON CONCENTRATION OF LYSINE IN PLASMA OF FINISHING CATTLE

High K intakes have been shown to affect lysine metabolism in swine and poultry. This effect may result in improved performance and its primary manifestation is a decrease in plasma and tissue lysine concentration. In order to evaluate the effects of supplemental K and crude protein (CP) on the concentration of amino acids in plasma (PLAA) and growth performance, 72 cattle (48 heifers + 24 steers, weighing 425 +/- 35 kg) were allotted to a 2 x 2 factorial arrangement of dietary treatments in a randomized complete block design trial. After 28 d on feed, there was a trend (P = 0.09) for an interaction effect of K (1 % KCl) and CP (6 % cottonseed meal) on plasma lysine. At 56 d there was an interaction (P = 0.02) of K and CP on plasma lysine. Supplemental K decreased (P = 0.01) plasma lysine in the absence of CP supplement, and increased it (P = 0.04) in the presence of CP. Supplemental CP decreased (P = 0.001) plasma lysine in the absence of supplemental K, but not in its presence. Addition of K, CP or both K and CP to the corn-peanut hull diet did not affect weight gain or feed efficiency. Addition of CP tended (P = 0.09) to increase feed intake over the entire trial. Carcass quality grade was lower (P = 0.03) for cattle fed CP supplement than for cattle not fed supplemental CP.