In order to test the hypothesis that the zinc to copper ratio is an important factor in determining the plasma level of cholesterol (Klevay, L.M. 1973. Am. .I. Clin. Nutr. 26:1060-1068, White Leghorn laying hens were fed normal energy (2764 kcal/kg) and low energy (2470 kcal/kg) practical diets containing varied ratios of zinc to copper. The levels of zinc and copper used were selected such that neither was nutritionally limiting nor toxic. No significant differences were observed between the control diet (fed for 4 wk before commencing the actual experiment) or any of the experimental diets with the cholesterol levels averaging 13.3 mg/g for egg yolk and 84.1 mg% for the plasma examples.
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