The influence of dietary selenium levels on blood levels of selenium and glutathione peroxidase activity in the horse.

This study explored the impact of dietary selenium supplements on the concentration of selenium and the activity of selenium-dependent glutathione peroxidase in the blood of mature male horses. The researchers found that selenium intake caused an initial increase in blood selenium levels, but these levels plateaued within five to six weeks. The activity of glutathione peroxidase, however, was unaffected by selenium intake.

Study Setup

• The researchers used 20 male horses averaging 535 kg for the study.
• The horses were randomly assigned to four different groups, each composed of five horses.
• All horses were fed a diet containing .06 ppm of naturally occurring selenium. However, this diet was supplemented with three different levels of selenium: .05, .10, and .20 ppm, given in the form of sodium selenite.

Data Collection

• Blood samples were taken for two weeks before the selenium supplements were included in the diets, and for 12 weeks after supplementation began.
• The researchers measured concentrations of selenium in the whole blood and plasma and evaluated the plasma glutathione peroxidase activities from all blood samples.

Study Findings

• Supplementing selenium in the diet led to a linear increase in plasma and whole blood selenium concentrations from the first week up to the fifth and sixth weeks, respectively. After this period, selenium concentrations did not significantly change in either supplemented or unsupplemented horses for the remaining 12-week experiment.
• The plateau levels of selenium in plasma ranged from .10 to .14 micrograms/ml, depending on the supplementation level, while those in the whole blood ranged from .16 to .21 micrograms/ml.
• The activity of selenium-dependent glutathione peroxidase in the plasma was not significantly affected, regardless of the selenium supplementation. Hence, this enzyme does not serve as a good indicator of dietary selenium in mature horses.