The Influence of Dietary Selenium Levels on Blood Levels of Selenium and Glutathione Peroxidase Activity in the Horse

Abstract

Twenty mature geldings, averaging 535 kg, were used to determine the influence of dietary selenium (Se) on the blood levels of Se and Se-dependent glutathione peroxidase (SeGSH-Px) activity in the horse. Horses were randomly assigned within breed to four treatments consisting of five horses each and fed a basal diet containing .06 ppm of naturally occurring Se. Diets were supplemented with .05, .10 and .20 ppm Se, as sodium selenite. Blood was drawn for 2 wk before, and for 12 wk following, the inclusion of supplement Se in the diets. Whole blood and plasma Se concentrations and plasma SeGSH-Px activities were determined from all blood samples. Selenium concentrations in plasma and whole blood increased linearly from wk 1 to wk 5 and 6, respectively, in Se-supplemented horses. After these times, no significant changes in Se concentration were observed in Se-supplemented or in unsupplemented horses throughout the remainder of the 12-wk trial. Plasma Se reached plateaus of .10 to .11, .12 to .14, and .13 to .14 micrograms/ml in horses supplemented with .05, .10 and .20 ppm Se, respectively. Whole blood Se reached plateaus of .16 to .18, .19 to .21, and .17 to .18 micrograms/ml in horses supplemented with .05, .10 and .20 ppm Se, respectively. Plasma SeGSH-Px activity was not significantly affected by dietary treatment. Therefore, this enzyme was not a good indicator of dietary Se in these mature horses.

Effect of selenium supplementation and source on the selenium status of horses1

“…This finding agrees with previous studies where no differences in the P GPx-3 activity were reported in Se-deficient humans or rats after consuming different sources of supplemental Se (Levander et al, 1983;Deagen et al, 1987). The lack of effect due to Se supplementation on P GPx-3 is similar to previous reports where P GPx-3 activity of horses did not respond to 12 wk of supplementation, even when plasma Se concentration showed an increase (Shellow et al, 1985). Fluctuating P GPx-3 activity, similar to that in the current study, was reported for horses fed Se-adequate diets by Podoll et al (1992).…”

“…Plasma Se concentrations of horses in the current study responded to supplementation over a relatively short time, having plateaued by d 28. This finding is similar to Shellow et al (1985), who reported that plasma Se concentrations of supplemented horses were greater than nonsupplemented horses after 2 wk of supplementation. It is worth noting that even though the CTRL diet provided 1.5 times the estimated requirement (NRC, 1989), the plasma Se concentrations of these horses were approximately 0.1 g/mL, compared with 0.14 g/mL previously reported by Shellow et al (1985) for horses receiving a similar amount of dietary Se.…”

“…This finding is similar to Shellow et al (1985), who reported that plasma Se concentrations of supplemented horses were greater than nonsupplemented horses after 2 wk of supplementation. It is worth noting that even though the CTRL diet provided 1.5 times the estimated requirement (NRC, 1989), the plasma Se concentrations of these horses were approximately 0.1 g/mL, compared with 0.14 g/mL previously reported by Shellow et al (1985) for horses receiving a similar amount of dietary Se. In the current study, plasma Se concentrations of horses fed diets containing supplemental Se providing approximately 0.45 mg of Se/kg of DM total diet were similar to previously reported plateaus of approximately 0.15 g/mL (Stowe, 1967;Maylin et al, 1980;Shellow et al, 1985).…”

“…Treatment means for d 0 plasma Se concentrations of horses fed CTRL and ORG diets reflect marginal Se status (0.053 to 0.120 g/mL) according to Puls (1994). The increase in plasma Se concentration in response to dietary Se supplementation reported in our study was expected because plasma Se concentration is sensitive to changes in dietary Se intake (Shellow et al, 1985;Stowe and Herdt, 1992). Plasma Se concentrations of horses in the current study responded to supplementation over a relatively short time, having plateaued by d 28.…”

Investigations on the Se-supply of horses in North West Germany

“…2). Wenn in den Untersuchungen von Shellow et al(1985) nach Se-Zulagen keine positive Reaktion gefunden wurde, so kann das an der bereits in der Kontrollperiode hohen GSH-Px-Aktivität gelegen haben, da nur bei zuvor marginaler Versorgung eine deutliche Anderung zu erwarten ist. Aufgrund vorgenannter Beziehungen dürften die Differenzen in der Plasma-GSH-Px-Aktivität zwischen Sommerund \ü/interhalbjahr auf Unterschieden in der Se-Aufnahme beruhen, da im Winter z. T. Misch-und Mineralfutter eingesetzt wurden, die im allgemeinen mit Selen supplementiert sind.…”