Measures of antioxidant status of the horse in response to selenium depletion and repletion.

The research investigates the role of selenium in affecting the antioxidant status and oxidative stress of horses. Through a monitored diet, changes to selenium levels led to shifts in the activity of a key enzyme and potential impacts on antioxidant status.

Research Context and Methodology

• The research involves studying the effects of selenium levels in the diet of horses and how these fluctuations impact antioxidants and generate oxidative stress. Selenium is considered significant due to its participation in the antioxidant mechanism via the selenoenzyme glutathione peroxidase (GSH-Px).
• Twenty-eight horses of different ages and genders were studied. These horses were divided randomly into four different dietary groups: low selenium (LS), adequate selenium (AS), high organic selenium (SP), and high inorganic selenium (SS).
• For a span of 196 days, LS, SP, and SS groups were given a low selenium diet while AS was given an adequate selenium diet. The next 189 days, the LS and AS maintained the same diet while the SP group was supplemented with selenium yeast and SS with sodium selenite.
• Blood samples were collected consistently throughout the study to monitor whole blood selenium and GSH-Px activity, serum vitamin E concentration, total antioxidant capacity (TAC), serum malondialdehyde (MDA), and triiodothyronine and thyroxine concentrations.

Research Findings

• Each dietary group exhibited different activity and concentration levels on the items under study as a result of the change in their selenium intake. Whole blood selenium and GSH-Px activity decreased in LS, SP, and SS during the selenium depletion phase, and increased in SP and SS with supplementation.
• By the end of the selenium supplementation, GSH-Px activity was found to be significantly higher in SP and SS compared to AS and LS groups.
• The Vitamin E status amongst all groups remained adequate throughout the study, with no significant differences observed between the different groups. This was a similar case with serum TAC which did not change in response to selenium depletion or repletion.
• Though serum MDA was higher for the AS group than the LS during depletion phase, there were no notable differences across the dietary groups after the supplementation phase.

Overall Conclusion

• The study determined that the change in selenium status, caused by alterations in dietary selenium intake, did not greatly impact total antioxidant capacity (TAC) or malondialdehyde levels (MDA). This could possibly be due to the maintained adequate Vitamin E status in the horses.
• However, supplementation of selenium at 0.3 mg/kg DM boosted GSH-Px activity beyond that of horses fed with an adequate diet based on the 2007 National Research Council recommendations. The higher activity implies a potential advantage in feeding higher selenium diets to horses living in low-selenium areas.