Sodium Selenite in dog and cat food

Is it OK for dogs and cats?

Dogs

Yes, at the levels used in complete dog foods. EU scientists (EFSA, 2016) judged sodium selenite a safe and effective selenium source for all animal species. Selenium is harmful in excess, and the EU caps total selenium in dog and cat food at 56.8 µg per 100 g dry matter. That cap is not far above FEDIAF's minimum for growing puppies (40 µg).

Cats

Yes, at normal levels, and the same EU cap applies. In a 2012 study, adult cats and dogs fed high levels of selenium for three weeks, from sodium selenite or an organic source, showed no signs of selenium poisoning. Cats got rid of excess selenium in urine more efficiently than dogs, so the authors concluded that cats can tolerate higher dietary selenium.

How settled this is: Limited by regulators

What sodium selenite is

Sodium selenite is an inorganic selenium salt. In it, selenium is in the selenite form (+4). The body can convert selenite into selenide, the form found in selenium-containing amino acids. US rules (21 CFR 573.920) allow selenium to be added to feed as sodium selenite or sodium selenate. They cap it at 0.3 ppm in complete feed for chickens, swine, turkeys, sheep, cattle and ducks; dogs and cats are not named in that section. The same section requires selenium premixes to carry a caution that adding higher levels is not permitted. In a 2016 opinion, EFSA judged sodium selenite a safe and effective selenium source for all animal species.

Why it is in pet food

Selenium is a required trace mineral. It is part of glutathione peroxidase, an enzyme that prevents oxidative injury, and of several enzymes involved in thyroid hormone balance. Plants take up selenium from soil, and soil selenium varies widely from region to region. FEDIAF notes that the minimum requirement of growing puppies has been measured at 0.21 mg per kg dry matter. It adds a safety margin because selenium in pet food may be poorly available. EFSA regards sodium selenite as an effective selenium source, so a measured amount can help a food reach recommended levels.

What it does in the food

Sodium selenite supplies selenium. FEDIAF's September 2025 minimums, per 100 g of dry matter, are as follows. Adult dogs: 18–27 µg, depending on energy intake and whether the food is wet or dry. Growing puppies and breeding dogs: 40 µg. Adult cats: 21–35 µg. Growing and breeding cats: 30 µg. For adult dogs and cats, FEDIAF sets higher minimums for wet foods than for dry foods; for growth and reproduction the wet and dry minimums are the same. FEDIAF says there are no data on the exact selenium needs of adult dogs, so it uses the cat allowance for them. The EU legal maximum for total selenium is 56.8 µg per 100 g dry matter for both species. Organic selenium supplements have a separate, lower cap of 22.73 µg per 100 g dry matter.

Safety and limits

Selenium is harmful in excess. The Merck Veterinary Manual describes selenium poisoning mainly in livestock and birds. It says poisoning usually follows long-term high intake, and sometimes dosing with badly formulated supplements. Merck gives 2 mg per kg of diet (2 µg/g) as the maximum tolerable level for dogs and cats. It puts dietary requirements for most species at 0.1 to 0.38 mg/kg. In a 2012 study, adult cats and dogs ate diets supplemented to 8–10 µg selenium per g dry matter for three weeks, from sodium selenite or organic selenium. None showed clinical signs of selenium poisoning. Compared with dogs, cats excreted more selenium in urine and stored less in the liver. The study lasted three weeks and did not test long-term intake. EFSA's 2016 opinion judged sodium selenite a safe and effective selenium source for all animal species. It judged it safe for consumers provided the total maximum authorised selenium content in complete feed is respected. It also found the additive irritating to skin, eyes and airways, and a skin sensitiser. It said workers handling it would breathe in selenium at levels that pose a risk.

What depends on the amount and the recipe

What counts is the total selenium from all ingredients plus the supplement, measured against the legal maximum. Plants take up selenium from soil, and soil selenium varies widely. FEDIAF's minimums are higher for growing puppies than for adult dogs. For adult dogs and cats they are also higher for wet than for dry foods. FEDIAF notes that selenium in pet food may be poorly available. The selenium source matters for EU limits, because organic selenium supplements have their own lower cap. Dogs and cats also differ: in a three-week study, cats handled high selenium intakes better than dogs.

Not the same as

• Selenium yeast — An organic selenium source: yeast grown with selenium salts, which take the selenium into their cells. It has its own listing in 21 CFR 573.920, and the EU caps organic selenium separately.
• Sodium selenate — A different inorganic selenium salt (selenate, +6, not selenite, +4). It is listed alongside sodium selenite in 21 CFR 573.920.
• Selenomethionine hydroxy analogue — A manufactured organic selenium compound with its own listing in 21 CFR 573.920.

Sources

1. 21 CFR 573.920 Selenium, Code of Federal Regulations, 2024 edition — U.S. Government Publishing Office (govinfo), 2024. Selenium may be added to feed as sodium selenite or sodium selenate; 0.3 ppm limit in complete feed for named livestock and poultry species (dogs and cats not named); premix caution statement; separate listings for selenium yeast and selenomethionine hydroxy analogue.
2. Selenium Toxicosis in Animals (Merck Veterinary Manual, full review Aug 2022, updated Sept 2024) — Merck & Co. / Merck Veterinary Manual, 2024. Selenium is a required trace mineral (requirements 0.1–0.38 mg/kg for most species); glutathione peroxidase and thyroid enzymes; selenite (+4) and selenate (+6) forms convert to selenide; plants take up selenium from soil, which varies widely; poisoning is described mainly in production animals and usually follows chronic high intake or badly formulated supplements; maximum tolerable level of 2 µg/g for dogs and cats.
3. FEDIAF Nutritional Guidelines for Complete and Complementary Pet Food for Cats and Dogs (September 2025) — FEDIAF – European Pet Food Industry Federation, 2025. Selenium minimums for dogs and cats (wet and dry, by life stage); EU legal maximum of 56.8 µg/100 g DM; organic selenium cap of 22.73 µg/100 g DM; puppy requirement of 0.21 mg/kg DM plus a safety margin for low availability; cat allowance used for adult dogs; the legal maximum covers total content.
4. EFSA FEEDAP Panel. Safety and efficacy of selenium compounds (E8) as feed additives for all animal species: sodium selenite. EFSA Journal 14(2):4398 — European Food Safety Authority (EFSA), 2016. Sodium selenite is a safe and efficacious selenium source for all animal species; safe for consumers provided the total maximum authorised selenium content in complete feed is respected; irritant to skin, eyes and the respiratory system; skin sensitiser; workers handling it would inhale selenium at levels that pose a risk.
5. Todd SE, Thomas DG, Bosch G, Hendriks WH. Selenium status in adult cats and dogs fed high levels of dietary inorganic and organic selenium. Journal of Animal Science 90(8):2549–2555 — Journal of Animal Science (Oxford University Press, peer-reviewed), 2012. Adult cats and dogs fed 8–10 µg Se/g DM from sodium selenite or organic selenium for 3 weeks showed no clinical selenosis; cats excreted more selenium in urine, had lower liver selenium, and can tolerate higher dietary selenium than dogs.

Checked against these sources on 2026-10-15. Definitions are in our own words. This is a reading aid, not veterinary advice: a vet who knows your animal comes first.