Metabolism of selenite, selenomethionine and feed-incorporated selenium in lactating goats and dairy cows

Abstract

The objective of this study was to investigate the metabolism of inorganic and organic Se sources at different dietary Se levels in lactating goats and dairy cows. The study consists of two experiments on goats dosed singly, either orally with grass sprayed with Na275SeO3 one week before cutting, intraruminally (I.R.) with Na275SeO3, or intravenously (I.V.) with Na275SeO3 or 75Se-selenomethionine. Follow-up periods were from 15 to 28 d long. Dietary Se levels were 0.05, 0.22 and 0.34 mg/kg DM. Values for 75Se absorption, excretion in milk, urine and faeces, 75Se activity in plasma, erythrocytes and hair are presented. In another experiment lasting 539 d, 48 dairy cows were fed either Na275SeO3 or grass silage sprayed with Na275SeO3 one week before cutting. Dietary Se levels were from 0.03 to 1.8 mg/kg DM. Se content in milk, plasma and erythrocytes, and GSH-Px activity in erythrocytes and plasma are given. True absorption of 75Se was 63 % and 65 %, and excretion of 75Se in milk 4 % and 7 % in the goats dosed I.R. with Na275SeO3 and orally with 75Se-labeled grass. The effect of dietary Se content was non-significant. After I.V. dose, 3.6 % and 33 % of 75Se was excreted in milk in goats dosed with Na275SeO3 and 75Se-selenomethionine, respectively, Na275SeO3 being eliminated mainly via urine. In cows receiving selenium as Na275SeO3, milk contained 0.011, 0.011, 0.016 and 0.020 mg Se/l at dietary Se levels 0.11, 0.17, 0.42 and 0.68 mg/kg DM, respectively. In cows receiving Se-sprayed silage, milk Se content was 0.023, 0.020, 0.029 and 0.040 mg/l when the diet contained 0.09, 0.20, 0.45 and 1.20 mg Se/kg DM. Se incorporated into silage was more efficient (p