High Rates of Selenium Supplementation for Sheep to Determine Selenium Retention via Forage Fertilization

Final Report to the Oregon Sheep Commission

June 20, 2008

Gene Pirelli, Professor, Department of Animal Sciences, Polk County Extension, P. O. Box 640, Dallas, OR 97338.  503-623-8395.

Tom Nichols, Sheep Center Manager, OSU Department of Animal Sciences, Corvallis, OR, 97331.  541-737-2903.

 Jean Hall, Department of Biomedical Sciences, College of Veterinary Medicine, Oregon State University, Corvallis, OR 97331.

Introduction

Many parts of the world are known to have soils deficient in the essential micronutrient selenium (Se), potentially leading to clinical signs of Se deficiency in livestock grazing or fed crops raised on them. Severe Se deficiency results in nutritional myopathy or "white muscle disease", whereas subclinical Se deficiency causes muscular weakness of the newborn, immunosuppression, unthriftiness, reduced weight gain, scours, infertility, abortion, and retained placenta.

Several means of administering Se to deficient ruminants have been developed with nearly a half-century of experience with Se supplementation . For example, there are several injectable preparations available, which often include vitamin E. Selenium can be added to feed, mineral, and protein supplements. Sustained-release boluses with a life of several months may be used. Because of their weight, these boluses stay in the rumen whereby they gradually release Se.

Selenium supplemented by these methods is usually inorganic sodium selenite or selenate. One limitation of supplementing with inorganic Se in salt or feed is the apparent short duration of Se storage in the animal. If Se is removed from the diet, blood Se concentrations may become deficient if they were initially in

the lower part of the normal reference interval. Seasonal grazing practices may result in limited access to Se-containing salt-mineral mixes for extended periods of time, and therefore sheep may be Se deficient by the end of the grazing season.

Gene Pirelli holding on the of test ewes as Tom Nichols draws a blood sample.