Nutritional toxicity of sulfur and sulfur-nutrient interactions in ruminants
Olkowski, Andrzej A.
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High dietary sulfur (S) in ruminants introduces a range of effects not seen in nonruminant animals. This thesis focuses on several new mechanisms through which S interacts with copper (Cu) and thiamine metabolism, and on more complex three way interactions of S-Cu-thiamine in ruminants. The present investigation comprises three field studies, one in vivo study, and one in vitro study. The field studies were conducted on Saskatchewan farms. These studies include investigations of: a) the effects of high sulfate in the drinking water on blood thiamine status, and b) nutritional aspects and selected biochemical parameters in herds with incidence of clinical problems associated with consumption of excess S in drinking water. Cattle exposed to high levels of S in drinking water had lower blood thiamine than those drinking water containing a low concentration of S. The occurrence of polioencephalomalacia (PEM) was documented in all of our field research. These studies also showed that Cu influences interactions between S and thiamine. Both Cu and thiamine depletion in the blood of cattle drinking water containing a high concentration of S can be corrected by dietary supplementation of Cu alone. Chronic effects of nutritional S toxicity were investigated using sheep as a model. This study confirmed the known effects of S on Cu metabolism. It was also observed that Cu influences the effect of S on thiamine metabolism, and that the interaction of S-Cu-thiamine occurs in the gastrointestinal tract as well as systemically. The in vivo study also showed that, in chronic nutritional S toxicity in ruminants, the target organ is the brain. The early, (subclinical) morphologic and metabolic lesions were evident as altered electrophysiological events along the auditory pathway. After prolonged exposure (three to eight weeks) several animals developed PEM. The incidence of PEM was attributed (p