Dietary supplementation with 6000 mg of Zn2+/kg of feed has been shown to modify the clinicopathologic expression of Brachyspira hyodysenteriaeinfection in a laboratory mouse model of swine dysentery. However, this concentration impaired the body weight gain of the mice. The purpose of the present study was to determine a minimal prophylactic concentration of feed-grade zinc compounds that would not affect the growth of mice challenge-exposed with B. hyodysenteriae. A total of 440, 6- to 8-week-old, C3H/HeN mice were allocated randomly to groups and fed either a defined diet or a defined diet containing either 1000, 2000 or 4000 mg/kg ZnO, ZnSO4 or zinc-methionine for 7 days before intra- gastric inoculation with B. hyodysenteriae. From days 7 to 35 after inoculation, mice in each group were necropsied at weekly intervals for determination of body weight, presence of B. hyodysenteriae in the cecum, and histological assessment of cecal lesions. Only ZnO fed at 2000 mg/kg had a prophylactic effect against B. hyodysenteriaeinfection without affecting the body weight gain of the mice. The prophylactic effect of Zn2+ against infection with B. hyodysenteriae was also affected by the relative concentration of Fe2+ and Zn2+/Fe2+ratio of the diet.