Zinc, copper and manganese in the alimentary tract of sheep.

I . The changes in the concentrations and solubilities of zinc, manganese and copper in the rumen, abomasum and along the small intestine of cannulated sheep, maintained on dried grass, have been determined. Relationships between the solubilities of the metals and the pH values of the samples were observed. 3. The pattern of change of solubilities could be reproduced in vitro by adjustment of the pH of rumen and abomasal samples. 3. By a combination of gel filtration and continuous-flow high-voltage electrophoretic techniques it was shown that soluble complexes of Zn and Mn occur in the rumen and lower regions of the small intestine. The soluble Zn and Mn in the abomasum, duodenum and upper jejunum appeared to exist in ionic form. The charge and molecular size of these complexes were found to be dependent on the pH of the samples. 4. From detergent treatment of rumen samples it appeared that much of the insoluble metal, particularly Cu, might be associated with microbial matter. 5. The significance of these findings and their relationship to the differences noted in the apparent requirements for trace elements of ruminants on different diets is discussed.