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Selenium - Se in dog and cat diets

A short guide to the role of Selenium - Se in dog and cat nutrition.

Selenium - Se

Selenium is a key antioxidant — it is a component of glutathione peroxidase and, together with vitamin E, forms a shield protecting cell membranes from damage [1] [2]. It is also essential for the conversion of thyroid hormones (T4 → T3 by selenium-dependent deiodinases) and supports the immune and reproductive systems. The NRC requirement for an adult dog is MR 35 µg, RA 87.5 µg / 1000 kcal ME (upper limit SUL 500 µg); in the cat the RA is 75 µg / 1000 kcal ME [1].

Where it's found: The best source is kidney, followed by liver, red muscle meat and saltwater fish (small species — sardines, sprats, herring — are better than large predators) [1]. Eggs are a valuable addition. Note: the selenium value in the calculator carries a large error, because its content in the raw material depends on region and feed — Polish soils are poor in selenium, so Polish meat tends to be low in it [2].

Deficiency: Rarely occurs on its own — it usually goes hand in hand with a lack of vitamin E. It leads to weakened immunity, deterioration of the coat, and in extreme cases to cardiomyopathy [2]. Cats fed monotonously on poultry alone, without kidney and fish, are particularly at risk.

Excess: Selenium has a narrow safety window. Chronic overdosing with supplements leads to selenosis: a characteristic garlic odor from the mouth, dulling and massive shedding of the coat, brittleness and deformation of the claws, and liver damage [3]. From natural sources (kidney, fish) an overdose is practically impossible — the risk arises only with supplementation. In the cat the error is easier to make due to its small body mass and very small working doses, although studies indicate that the cat's species tolerance to selenium is at least as good as the dog's [4].

What to watch for

Selenium and vitamin E work together — with a diet rich in polyunsaturated fatty acids (oily fish, fish oil) the requirement for both nutrients rises, so "selenium within norm" may not be enough if vitamin E is too low [1]. With frequent feeding of saltwater fish, part of the selenium is used up binding mercury. The best strategy is variety of natural sources: regular kidney, rotation of meats, and occasional small saltwater fish. If supplementation is necessary — only selenomethionine or selenium yeast in microdoses, never sodium selenate, preferably after consulting a nutritionist [5].

Sources

  1. National Research Council (2006). Nutrient Requirements of Dogs and Cats. National Academies Press. https://nap.nationalacademies.org/catalog/10668/nutrient-requirements-of-dogs-and-cats
  2. Zentrichova V, Pechova A, Kovarikova S (2021). Selenium and Dogs: A Systematic Review. Animals 11(2):418. https://pmc.ncbi.nlm.nih.gov/articles/PMC7915357/
  3. Merck Veterinary Manual. Selenium Toxicosis in Animals. https://www.merckvetmanual.com/toxicology/selenium-toxicosis/selenium-toxicosis-in-animals
  4. Todd SE, et al. (2012). Selenium status in adult cats and dogs fed high levels of dietary inorganic and organic selenium. https://pubmed.ncbi.nlm.nih.gov/22307479/
  5. Hand MS, Thatcher CD, Remillard RL, Roudebush P, Novotny BJ (2010). Small Animal Clinical Nutrition, 5th Edition. https://www.markmorrisinstitute.org/sacn5.html