Research in humans and laboratory animals has documented that Zn deficiency impairs immune responses and reduces disease resistance . Severe Zn deficiency in calves and in lambs has also been shown to impair immunity. In cattle fed practical diets marginal deficiency is more likely to occur than severe Zn deficiency. Controlled studies with growing cattle and lambs suggest that marginal Zn deficiency does not impair cellmediated or humoral immune responses. Plasma Zn concentrations decrease in dairy cows at parturition and return to baseline values within 3 days. However, the effect of dietary Zn on immune function in peri parturient cows has received little attention.