Relationship of Dietary Selenium to Selenium in Plasma and Milk from Dairy Cows

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Abstract
In a 13 wk trial Holstein cows in mid-lactation were fed 4 diets containing natural Se alone or supplemented with 0.1, 0.2 or 0.5 mg of inorganic Se/kg of diet. Dietary Se-concentration averaged 0.334, 0.385, 0.456 and 0.772 mg/kg. Se plasma in wk 7 averaged 0.112 .mu.g/ml with no differences among treatments; milk Se ranged from 0.040-0.046 .mu.g/ml and was higher in the 2 higher Se diets. In wk 13 Se in plasma and milk averaged 0.119 and 0.054 with no treatment differences. The 7 and 13 wk concentrations were higher than pretrial 0.084 and 0.033 .mu.g/ml for plasma and milk during which time dietary Se concentration was 0.254 mg/kg. Se concentration increased linearly from about 0.08-0.120 .mu.g/ml of plasma and about 0.030-0.055 .mu.g/ml of milk as intake of Se increased from about 2-6 mg/day. Increase in Se intake from 6-12 mg/day resulted in little change in plasma and milk Se. Moderate concentrations of dietary Se (0.3-0.7 mg/kg) did not result in toxic amounts of Se in milk.