Effect of Different Selenium Supplementation Practices in Oregon on Whole-Blood Selenium Concentrations, Naturally Acquired Parasite Infections, and Inflammatory Mediators of  Subclinical Inflammation in Ewes

Background

The focus of our selenium (Se) research is to improve health, prevent diseases, and increase productivity in sheep flocks across Oregon, where soils are deficient in Se. Deficiencies in the Se content of forages are reflected in whole-blood (WB) Se concentrations in sheep consuming these forages. WB-Se concentrations from 56 farms in Oregon showed that 16% had deficient WB-Se concentrations in 100% of the ewes tested, and 23% had >50% of ewes tested with WB-Se deficiency (Hasan et al. unpublished data). Thus, subclinical Se deficiency is quite common in Oregon flocks of sheep, even when owners are providing their animals some form of Se supplement. We have previously shown that feeding selenate-fertilized forages not only increased WB-Se concentrations in sheep and cattle, but also improved their productivity and health. We are interested in how subclinical Se deficiency makes sheep prone to diseases, and what small molecules (i.e., cytokines) regulate these effects. A normal inflammatory response requires a balance between sufficient cytokine production to eliminate the pathogen and avoidance of a hyperinflammatory response in which an overabundance of cytokines causes clinically significant collateral tissue damage. To better understand how Se supplementation affects inflammation and subclinical disease, we measured WB-Se concentrations from healthy ewes on seven different farms in Oregon, each of which had their own unique Se-supplementation program. We also looked at fecal egg counts thinking gastrointestinal parasitism susceptibility might be correlated to WB-Se status. Finally, we measured six different cytokines in the serum from these ewes to see if cytokine concentrations were correlated to WB-Se concentrations or GI parasite load. Our goal was to show a mechanism of how WB-Se concentrations affect inflammation and underlying health and productivity.