PROPHYLACTIC EFFECT OF DIETARY ZINC IN A LABORATORY MOUSE MODEL OF SWINE-DYSENTERY

Reduced prevalence of diarrhea and mortality has been reported after d ietary supplementation with zinc compounds in swine with naturally acq uired colibacillosis and those challenge-exposed with Serpulina hyodys enteriae; however, the usefulness of this approach for control of ente ric diseases of swine remains to be determined. To examine the effect of dietary zinc-containing compounds on the colonization and developme nt of cecal lesions associated with S hyodysenteriae infection, a defi ned diet alone or with added ZnO, ZnSO4, or Zn-methionine complex to a final concentration of approximately 6,000 mg of Zn2+/kg of complete feed was fed ad libitum to 156 female mice (strain C3H/HeN) for 10 day s prior to oral. inoculation either with S hyodysenteriae or sterile t rypticase soy broth. Rations were continued for 42 days, while at week ly intervals, 3 mice/group were necropsied for determination of body w eight, cecal weight, liver zinc concentration, presence of S hyrodysen teriae in the cecum, and gross and histologic assessments of cecal les ions. From postinoculation day 0 to 42 the liver zinc concentration of mice fed the zinc-supplemented diets was approximately twice that of mice fed the basal diet, irrespective of the source of zinc. From post inoculation day 7 through 42, the overall recovery rate of S hyodysent eriae in infected mice fed the basal diet was 77.8%. In contrast, reco very rates of S hyodysenteriae from S hyodysenteriae-inoculated mice f ed the zinc-supplemented diets were 0% for Zn-methionine and ZnO and 1 6.7% for ZnSO4. Mice fed the basal diet had significantly (P < 0.05) h igher weight gain than mice fed the zinc-supplemented diets. However, the severity of cecal lesions, as determined by histologic examination and quantitative determination of longitudinal crypt length of the ce cum was significantly (P < 0.05) less in mice fed the zinc-supplemente d diets than in mice fed the basal diet. Data from this study indicate that dietary supplementation with 6,000 mg of zinc/kg of feed signifi cantly reduced the recovery rate of S hyodysenteriae and provided part ial protection against development of cecal lesions in mice inoculated with S hyodysenteriae. However, at this concentration, zinc had a del eterious effect on growth of the mice.