Updated October 11, 2026. Fact-checked against veterinary sources; review by a licensed veterinarian is in progress. See our editorial policy.
Quick answer: The best nutritional support for a pet’s immune system is a complete, balanced diet and a healthy weight. Some nutrients, such as antioxidants like vitamin E, omega-3 fatty acids, and certain probiotics, have shown effects on immune markers in studies, but no supplement has been proven to prevent illness in healthy pets. Vaccines, parasite prevention, dental care, and regular checkups protect pets far more than any “immune booster.”
What supports immune health
- A complete and balanced diet for your pet’s life stage
- Healthy weight: obesity is linked to chronic inflammation
- Vaccinations as your vet recommends
- Parasite prevention
- Dental care
- Exercise, enrichment, and low stress
- Regular vet checkups to catch problems early
Nutrients and supplements with some evidence
- Antioxidants (vitamin E, vitamin C, beta-carotene): studies in dogs and cats show changes in immune markers, particularly in older pets. Many complete diets already include them.
- Omega-3 fatty acids (EPA and DHA): anti-inflammatory effects, with evidence for skin, joint, and kidney health.
- Probiotics: some strains have shown benefits, such as reducing diarrhea in shelter cats and kittens. Effects are strain-specific.
- Prebiotic fibers: support healthy gut bacteria.
Evidence for other “immune” supplements, such as mushroom blends, colostrum, and herbal products, is limited in pets.
Pets with weakened immunity
Pets with FeLV, FIV, cancer, diabetes, or those on immune-suppressing medications need extra care:
- Avoid raw meat, raw eggs, and unpasteurized milk, which carry bacteria.
- Keep food and water bowls clean.
- Check with your vet before starting any supplement, since some interact with treatment.
What to avoid
- Megadoses of vitamins or minerals, which can be harmful, especially vitamins A and D.
- Human supplements, which may contain xylitol, garlic, or doses not suitable for pets.
- Garlic or onion “immune” remedies, which damage red blood cells in dogs and cats.
- Essential oils given by mouth.
- Supplements in place of vaccines or treatment.
Choosing a supplement
- Ask your vet whether your pet needs one.
- Choose products made for pets, with a quality seal such as the National Animal Supplement Council (NASC).
- Introduce one at a time and watch for stomach upset.
Frequently asked questions
Do healthy pets need immune supplements?
Usually not, if they eat a complete and balanced diet.
Can diet prevent infections?
Good nutrition supports overall health, but vaccines and parasite prevention are the proven ways to prevent many infections.
Sources
- Merck Veterinary Manual: Nutrition in small animals
- Bybee SN, Scorza AV, Lappin MR. Effect of the probiotic Enterococcus faecium SF68 on presence of diarrhea in cats and dogs housed in an animal shelter. J Vet Intern Med. 2011
- Heaton PR, et al. Role of dietary antioxidants to protect against DNA damage in adult dogs. J Nutr. 2002
- WSAVA Global Nutrition Committee: Guidelines on selecting pet foods
This article is for general education and is not a substitute for care from your own veterinarian. Learn about The Pet Vet and our editorial policy.