Selenium Benefits and Feeding

ImmunityIngredientsMeongsiljang Veterinary Advisory Board

Selenium is an essential mineral that supports your dog’s or cat’s immune system and thyroid function. We’ve put together a guide covering recommended dosages and important precautions to avoid excess.

What Is Selenium?

Selenium is an essential trace mineral that helps dogs and cats produce antioxidant enzymes and protect their immune cells. The most important thing is proper dosage. A deficiency can weaken the immune system and cause muscle abnormalities, while too much can lead to toxicity. Since most commercial pet foods already contain adequate amounts, you should not supplement it without professional guidance.

The Role of Selenium

Selenium plays a variety of roles in the body, serving as a key component of the antioxidant system that protects cells from damage.

Antioxidant activity: Selenium is a constituent of glutathione peroxidase (GPx), which helps protect cells from free radicals and oxidative stress.

Immune-related functions: As an essential trace mineral, selenium is necessary for normal physiological functions overall, and its relationship with immune function is also being studied.

Thyroid function: Selenium is a component of selenoenzymes (deiodinases) involved in thyroid hormone metabolism. Studies in ruminants have reported that selenium deficiency impairs the conversion of T4 to T3 in tissues. In cats, research has shown that higher selenium concentrations in diet are associated with increased serum T3 levels, demonstrating a positive correlation between serum selenium and T3.

Reproductive health: Because there is no direct data on the amount of selenium required during pregnancy and lactation, it is assumed that adequate levels during growth (0.3 mg per kg of diet, based on 4,000 kcal) are also appropriate for reproductive health.

Muscle health: Deficiency can lead to skeletal muscle degeneration and edema, as well as myocardial abnormalities, including myocardial cell degeneration and subendocardial necrosis.

Selenium at a Glance

Caution

셀레늄(Selenium)

항산화·면역력·갑상샘 기능 지원

Dosage: 강아지 약 87μg/1000kcal, 고양이 약 75μg/1000kcal

미국국립연구위원회 권장

What Does Veterinary Research Say?

The National Research Council (NRC) classifies selenium as an essential trace mineral for both dogs and cats. According to veterinary nutrition textbooks, selenium content in feed ingredients varies significantly depending on the type of ingredient and the selenium concentration in the soil where the grains were grown, and selenium levels in animal tissues also vary based on the selenium concentration in the diet. The relationship between selenium and thyroid hormone metabolism has been reported in ruminants, where deficiency impairs the conversion of T4 to T3. In cats, studies have shown that higher dietary selenium concentrations are associated with increased serum T3 levels, demonstrating a positive correlation between serum selenium and T3. However, evidence suggesting that this association directly causes specific diseases remains limited. In terms of bioavailability, dry (extruded) food (approximately 53%) has been reported to have a higher selenium absorption rate than canned food (approximately 30%).

Recommended Dosage (Based on National Research Council Guidelines)

For adult dogs, the recommended intake is approximately 87 μg per 1,000 kcal, while for adult cats, it is about 75 μg per 1,000 kcal. Most pets eating commercially available complete diets already meet these requirements. If you are considering additional supplementation, it is essential to consult with your veterinarian first, as the necessary amount varies depending on your pet's weight, health status, and the composition of their current food.

Foods High in Selenium

There are several natural dietary sources of selenium suitable for dogs and cats.

Animal-based proteins: Salmon, tuna, egg yolks, and chicken liver are particularly rich in selenium.

Organ meats: Selenium is highly concentrated in organs such as the liver and kidneys.

Seafood: Sardines and shrimp are also excellent sources.

Brazil nuts: While they are the top source for humans, feeding them directly to pets is not recommended.

Yeast extract: This form, commonly found in commercial pet foods and supplements, offers high bioavailability.

Deficiency and Excess Symptoms

Deficiency symptoms: Signs may include skeletal muscle degeneration and edema, cardiac abnormalities (myocardial cell degeneration and subendocardial necrosis), loss of appetite, and difficulty breathing. However, these issues are rare in pets that consistently eat only commercially available pet food.

Excess (toxicity) symptoms: Excessive selenium intake can cause hypochromic microcytic anemia and severe liver damage (hepatocyte necrosis and cirrhosis). With chronic exposure, reports have noted dry skin and coat, gait abnormalities (lameness), periosteal proliferation around joints, tooth discoloration, and enamel defects. Risks increase when supplements are combined without veterinary guidance or when organ meats are fed in excess on a daily basis.

Precautions When Administering Selenium Supplements

Selenium is a mineral that can cause serious toxicity, such as anemia or liver damage, if consumed in excess, just as it poses problems when deficient. According to textbook reports, the selenium concentration in feed that caused toxicity in dogs (approximately 5.0 mg/kg) was significantly higher than recommended levels. However, this does not mean you should feel safe supplementing arbitrarily, as cumulative intake can still lead to danger. If your pet is already consuming a comprehensive supplement or a complete diet, adding a separate selenium product may result in duplicate intake. Furthermore, cats require even greater caution because there is insufficient data to establish a safe upper limit (SUL). For pets with thyroid, kidney, or liver disease, you must consult your veterinarian before deciding whether to administer selenium.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Will giving a dog Brazil nuts help supplement its selenium intake?

We do not recommend it. A single Brazil nut contains a very high amount of selenium, which can reach toxic levels in small dogs in just one serving. Additionally, its high fat content poses a risk of pancreatitis.

Can I give my pet a separate selenium supplement to boost their immune system?

For pets eating a complete and balanced diet, supplements are usually unnecessary. If a deficiency is suspected, it’s safest to have blood tests done and follow your veterinarian’s recommendation on whether to supplement.

What is the relationship between feline hyperthyroidism and selenium?

Selenium is a key component of selenoenzymes involved in thyroid hormone metabolism. In ruminants, selenium deficiency has been reported to impair the conversion of T4 to T3 in tissues. Studies in cats have shown that higher selenium levels in diet are associated with increased serum T3, with a positive correlation between serum selenium and T3 levels. Additionally, selenium content has been reported to be higher in wet (canned) cat food than in dry kibble. However, this association does not necessarily mean that selenium directly causes hyperthyroidism. If you suspect your cat has hyperthyroidism, do not adjust selenium intake on your own; instead, follow your veterinarian’s diagnosis and guidance for proper management.

Do pregnant or nursing pets need more selenium?

Nutritional needs increase overall during pregnancy and lactation, but feeding a diet specifically formulated for pregnant cats or dogs ensures adequate selenium intake, so no additional supplementation is necessary.

How can you tell if there’s a selenium deficiency through testing?

We assess selenium levels through serum and whole blood tests, as well as by measuring glutathione peroxidase activity. If skin or coat abnormalities and muscle weakness persist, please consult your veterinarian.