Effect of Se source and dose on selenomethionine and selenocysteine levels in blood and plasma of mature horses.

The study comprised 25 mature horses and incorporated five dietary treatments;�;�;�;�;�;�;� a negative control (C: 0.085 mg Se/kg DM), 3 levels of Se yeast supplementation, obtained from Saccharomyces cerevisiae CNCM I-3060 (OS2, OS3 and OS4: 0.2, 0.3 and 0.4 mg Se/kg DM respectively) and one positive control supplemented with Na selenite (IS3: 0.3 mg Se/kg DM). Diets were offered for 112 days. Total Se, proportion of total Se comprised as selenomethionine (SeMet) or selenocysteine (SeCys) of pooled samples of blood and plasma for each treatment at d 0.56 and 112 were determined. Total Se and SeCys increased both in blood and plasma during the trial in all treatments supplemented with Se; these increases were proportional to the level of dietary Se supplementation. ���������������������������������������������The SeMet increased only in treatments supplemented with Se yeast, with increases proportional to the level of dietary Se supplementation. In Se yeast horses the proportion of total Se comprised as SeMet accounted for 20 and 14% of total Se increase in blood and plasma respectively; in IS3 only accounted for 5 and 3% respectively. These results seem support the view that SeMet is a non-specific form of Se that is metabolized as a constituent of the methionine pool, and ���can be considered as a storage form of Se in higher animals�