A Close Look at a tiny Pet Food Ingredient, Selenium

Read the fine print of many pet foods, and you’ll find the ingredient sodium selenite. More than 90% of pet foods include sodium selenite in their recipies, the other pet foods have chosen a safer alternative. Why? Everything you wanted to know about Selenium, but probably didn’t know you should ask.

Selenium is an essential element necessary in trace amounts in the diet of humans and animals. Fish, meat, poultry, whole grains, and dairy products are typical sources of this nutrient in the human diet. AAFCO and the FDA approve a selenium supplement to animal diets, most commonly in the form of sodium selenite for pet foods. Although it sounds simple enough, there is far more to the selenium story.

The Journal of American College of Nutrition reports not much was known about which selenium compounds to approve for use in animal feeds when the decisions were made back in the 1970’s. “At the time the regulatory action was taken, only the inorganic selenium salts (sodium selenite and sodium selenate) were available at a cost permitting their use in animal feed.” http://www.jacn.org/cgi/content/full/20/1/1 Science has since learned that these inorganic selenium sources (sodium selenite most commonly used in pet foods) can be toxic in high doses; effecting an animal’s blood, liver, and muscles. The organic selenium yeast on the other hand, has proven to be far less toxic, even in large doses. “A study with rats showed that high doses (1.5 and 3.0 mg/kg body weight) of organic selenium in Selenium Yeast did not have any toxic effects after 14 days. This level of selenium is much higher than the theoretical toxic level for inorganic selenium.” http://www.nutriteck.com/bulk/selenium.html

So far, just to recap…selenium is a necessary element of a pet’s diet, furthermore selenium yeast has proven to be the safe delivery method of selenium to our pets in their food. Knowing this, why is the possible toxic sodium selenite the most popular delivery method of selenium in pet foods (in more than 90% of pet foods)?
The selenium plot thickens. Backing up a bit, Eco-USA explains that selenium is a “naturally occurring substance that is widely but unevenly distributed in the earth’s crust and is commonly found in sedimentary rock. Selenium is not often found in its pure form but is usually combined with other substances. Much of the selenium in rocks is combined with sulfide minerals or with silver, copper, lead, and nickel minerals. When rocks change to soils, the selenium combines with oxygen to form several substances, the most common of which are sodium selenite and sodium selenate.” Furthermore, in some parts of the US, the soil contains such high levels of non-organic sodium selenite, animals grazing on plants in these areas can be harmed. http://www.eco-usa.net/toxics/selenium.shtml

Why are plants and animals consuming varying amounts of sodium selenite a potential problem to pet food?
• Common grains used in pet foods can have varying levels of sodium selenite depending on the soil in different areas of the U.S. A batch of pet food using grain grown in Western States can have a much higher level of sodium selenite than grains grown in Eastern States. Pet owners have no knowledge of how much sodium selenite is included with each grain ingredient in their pet’s food.
• Depending on the sodium selenite levels of grains fed to meat producing animals (or by-product producing animals), and furthermore, depending on added sodium selenite levels of commercial feeds provided to these meat or by-product producing animals, every meat ingredient and by-product ingredient can vary to levels of sodium selenite.
• Add in to the potential toxic build up, the actual sodium selenite supplement added directly into your pet’s food.

If all the wrong pieces of the puzzle fall into the wrong place, your pet’s food, the result can be toxic.

“Humans who have accidentally eaten large amounts of selenium had upset stomachs, muscular weakness, difficulty in breathing, and pulmonary edema. Information about the health effects from eating or drinking too much selenium over long periods of time has come from areas in China with very high selenium levels in the soil and in the rice and vegetables people eat. These people had loss of hair, loss of and poorly formed nails, problems with walking, reduced reflexes, and some paralysis when exposed to levels of 1.64 ppm or higher selenium in their food over months to years.” http://www.eco-usa.net/toxics/selenium.shtml

ScienceLab.com states sodium selenite “may be toxic to blood, kidneys, liver, skin, central nervous system. Repeated or prolonged exposure to the substance can produce target organs damage. Repeated exposure to a highly toxic material may produce general deterioration of health by an accumulation in one or many human organs.” http://www.sciencelab.com/msds.php?msdsId=9927277

The simple solution, as recent science has proven, seems to be adding non-toxic selenium yeast to animal feeds including pet foods. “Of about one dozen supplementation studies, none has shown evidence of toxicity even up to an intake level of 800 microg Se/d over a period of years. It is concluded that Se-yeast from reputable manufacturers is adequately characterised, of reproducible quality, and that there is no evidence of toxicity even at levels far above the EC tolerable upper intake level of 300 microg/d.” http://www.ncbi.nlm.nih.gov/pubmed/15522125

The FDA listened to research and approved selenium yeast to be used in chicken feed in 2000, cattle feed in 2007, and as well recently approved the safer selenium yeast for use in dog foods. No word from the FDA as to when approval for use of selenium yeast in cat foods; I requested this information from the FDA on 3/24/08 and have received no response. The FDA should immediately approve selenium yeast for use in cat foods; there is no apparent excuse for the delay. Cat owners are urged to write the Center for Veterinary Management area of the FDA and (politely) encourage approval for use of selenium yeast in cat food.

Sadly, despite a wealth of research that proves sodium selenite can be toxic to animals including our pets, a large majority of pet food manufacturers continue to use sodium selenite instead of the scientifically proven safer alternative selenium yeast. Many pets could be suffering from an overdose of non-organic selenium without our knowledge.

Read the fine print of your pet’s food ingredient list; although it’s a tiny ingredient, sodium selenite might not be an ingredient you want to be listed in your pet’s food.

Wishing you and your pet(s) the best,

Susan Thixton
Pet Food Safety Advocate
Author, Buyer Beware
Co-Author Dinner PAWsible
TruthaboutPetFood.com
PetsumerReport.com

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