Selenium Yeast for Dairy Cattle

Dr. Bill Weiss, Dairy Nutrition Specialist, Ohio State University

A few months ago, the Food and Drug Administration (FDA) approved the use of selenium (Se) yeast for dairy and beef animals. Prior to this approval, sodium selenite and sodium selenate were the only approved sources of supplemental Se. In Ohio, all diets fed to dairy animals (calves, heifers, and dry and lactating cows) should be supplemented with the maximum legal amount of Se (currently 0.3 ppm). The question is, "Should you use inorganic Se (selenite or selenate) or Se-yeast?" The inorganic sources are substantially less expensive per unit of Se than Se-yeast, and based on clinical responses, they appear to work adequately in most situations. Based on enzyme responses, the Se in Se-yeast under normal conditions is 10 to 20% more available than inorganic Se. Under conditions that reduce Se absorption, Se-yeast may be substantially more available than inorganic Se. The most common situation in which Se absorption is impaired is when cows consume large amounts of sulfate. Dietary sulfate is usually not a problem; however, in certain areas of Ohio, water can contain very high concentrations of sulfate. In an experiment conducted at OARDC, sulfate intake equivalent to drinking water with approximately 300 ppm sulfate-sulfur (900 ppm sulfate) reduced absorption of Se from selenate by 20% compared to cows fed no sulfate.

Cows fed Se-yeast consistently have much higher concentrations of Se in milk, colostrum, and muscle than cows fed an equal amount of Se from inorganic sources. The increased Se concentration in milk and muscle may help improve human diets. Feeding Se-yeast to dairy cows during the dry period should improve the Se status of baby calves. The calf will be born with higher concentrations of Se in tissues, and colostrum from cows fed Se-yeast is very high in Se. Improved Se status of calves has been related to improved calf health.

In conclusion, replacing inorganic Se with Se-yeast will increase feed costs probably by 2 to 4 cents per head per day. Under normal conditions, the improved availability (10 to 20%) of Se-yeast will not greatly change Se status of cows. Se-yeast should be considered in areas that have water with high concentrations of sulfate. The addition of Se-yeast to diets for dry and prefresh cows may improve calf health. The current regulation allows feeding both inorganic Se and Se-yeast as long as total supplemental Se does not exceed 0.3 ppm of the diet.