Using Selenomethionine for cats

Charlie & Cloe

By Cat, Oct 2018; updated Aug 2019 at bottom of page (Photo, right, by Cat)

I’ve been updating my article on Beware of Toxic Sodium-Selentie in Pet Food as I try to find a source of cat food that uses Selenium-Yeast (Se-Yeast) instead of the toxic sodium selenite form.  Unfortunately, while the rules for pet food allow Se-yeast in dog food, they do not allow it in cat food, so I’m stuck.

My naturopath (1) suggested giving my cats some of the L-selenomethionine supplement that I take for myself – since it is an organic, chelated compound found naturally in certain foods such as “Brazil nuts, cereal grains, soybeans, and grassland legumes” (2), it is not a toxic form of selenium.

He suggested I  use the recommended amount of selenium for people, to determine the amount for my cats, based on weight, and then give them appropriate amount of SeM that will provide that amount of Se. Recommended daily allowance for humans is  200 mcg selenium for a 150-pound human, or 1.33 mcg Se per pound of human or cat.

My cats weight about 12 pounds each, so they need about 16 mcg Se per cat, which can be found in 40 mcg SeM. How did I determine this?

  • The molecular weight of SeM is 196 grams/mole, of which the selenium is 79 grams/mole. That means that in one 200 mcg capsule of SeM, there is about 80 mcg elemental selenium.
  • My cats each weigh about 12 pounds; that means 1 cat needs 16 mcg selenium (as 80 mcg Se/200 mcg SeM) mcg/cat) each daily.
  • So one capsule containing 200 mcg Selenium will serve 1 cat for about 5 days, or 2 cats for 2.5 days.

I’ll see how much water is needed to dissolve one capsule of SeM, and will then mix that into their food.

August 2019 update: For the last 10 months I’ve been mixing ½ capsule (100 mcg Se) of Thorne-brand SeM (without dissolving in water) in a 5.5 oz can of Friskies canned cat food (paté). One can feeds my 2 cats for 2.5 days (along with their Acana Se-free kibble), followed by a can without added SeM for 2.5 days. Thus ½ capsule (100 mcg Se) over 5 days for 2 cats, or 50 mcg Se over 5 days/cat; averaging 10 mcg selenium/cat/day.

Thus each cat is getting an average of 10 mcg selenium/day, which is a bit less than the recommended 16 mcg/day. So far, they remain healthy and as active as a 14-year-old cat can be.


  1. Dr Steven Gordon, ND, Whitefish MT

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