Omega-3 Dose for Cats: mg/kg to Millilitres

Omega-3 dosing in cats is a milligram problem, not a milliliter problem. The maintenance range is 20 to 40 mg per kg per day of combined EPA and DHA; joint and kidney cases are often run at 40 to 100 mg/kg under veterinary direction; and a typical fish oil at 300 mg per ml turns a 4 kg cat's 120 mg into 0.4 ml.

Three numbers catch most owners out: the bottle states fish oil in mg, not EPA plus DHA; the capsule is usually 1000 mg of oil holding only 250 to 320 mg of the 2 fatty acids; and the dose has to be held for 6 to 8 weeks before any judgement is fair.

Why the dose is per kilogram

EPA and DHA are absorbed and distributed by body mass, so a 3 kg cat and a 6 kg cat on the same 0.5 ml are on doses that differ by 2 times. At 300 mg per ml, 0.5 ml is 150 mg, which is 50 mg/kg for the 3 kg cat and 25 mg/kg for the 6 kg one. Same syringe, double the dose.

Weigh the cat, then multiply. A 4.2 kg cat at 30 mg/kg needs 126 mg a day; the same cat at 80 mg/kg for arthritis needs 336 mg, which is 1.1 ml of a 300 mg per ml oil.

Milligrams into milliliters

Read the label for EPA and DHA separately, add them, and ignore the front panel. A 1000 mg capsule with 180 mg EPA and 120 mg DHA delivers 300 mg of what counts, enough for 1 day for a 4 kg cat at 75 mg/kg, or 2 days at 37 mg/kg. A liquid at 300 mg per ml is the same math in spoons: 1 ml equals 1 capsule of that strength, so 1 ml and 1 capsule are interchangeable at that concentration.

Use a 1 ml syringe with 0.1 ml marks, not a teaspoon, because a teaspoon is 5 ml, roughly 10 times a 0.5 ml dose. Store the syringe separately and wipe the outside, since fish oil on the rim goes rancid within days.

The maintenance band: 20 to 40 mg/kg

For a healthy adult cat on a complete diet, 20 to 40 mg/kg covers the skin and coat use that most owners start with. Split it into 2 meals if the volume passes 0.5 ml, and give it with food that contains at least 3 g of fat, because bile release and micelle formation need fat in the same meal.

Expect 6 to 8 weeks before judging coat condition, and 8 to 12 weeks for anything joint-related. Stop at 12 weeks and reassess if there is no change, rather than doubling the dose on week 3.

Higher doses: joints and kidneys

Musculoskeletal use commonly runs 40 to 80 mg/kg, and kidney cases with proteinuria are sometimes taken to 100 mg/kg, always with the vet who is managing the kidney values. A 4 kg cat at 100 mg/kg is 400 mg, or 1.3 ml of a 300 mg per ml oil, which is a volume most cats will still take split over 2 meals.

Ramp up: start at 25 to 50 percent of the target for 5 to 7 days, then add a quarter of the target every 4 days. Loose stool is the dose-limiting side effect, and it appears far more often when the full dose starts on day 1.

Bleeding risk and the 7 to 10 day rule

EPA shifts platelet aggregation, so at 40 mg/kg and above, stop 7 to 10 days before any surgery, including a dental with extractions. A 4 kg cat at 100 mg/kg has a meaningful load, and 10 days is the safer end of the window for a cat with 4 or more extractions planned.

Watch for gum bleeding that takes over 5 minutes to stop, blood in the stool, or new bruising on the belly. Those signs at a high dose mean stop and call, not reduce by half. Cats on meloxicam or another NSAID, or on clopidogrel, need the combination cleared first.

Oxidation: the part that decides whether it works

Rancid oil is worse than no oil. Buy a product with a peroxide value under 10 mEq/kg and a TOTOX under 26, in a dark bottle, ideally nitrogen flushed. Once opened, refrigerate, use within 90 days, and write that date into a care calendar so it is not guesswork; a 250 ml bottle at 0.4 ml a day lasts about 625 days, nearly 7 times the safe window, so buy 60 to 120 ml.

Smell it monthly: fresh fish oil smells faintly of the sea, oxidized oil smells of paint or old nuts. Pricked capsules go in food within 24 hours. Never store oil above 25 C or in sunlight, and never add it to food that will sit out for hours.

Calories, stool, and interactions

Fat carries 9 kcal per gram, so 1 ml of oil is about 0.9 g and 8 kcal; 1.3 ml adds 12 kcal, which is 5 percent of a 230 kcal day. That matters in a cat that is already losing weight, and it matters more in a cat on a renal diet with a tight phosphorus budget, so check the share against the day's calories with a food calculator.

Soft stool at the target dose usually settles with a 25 percent reduction plus splitting into 3 meals. Persistent diarrhea, vomiting, or a fishy smell on the breath within 30 minutes of the dose means the product, not the cat, is the problem.

Dose table by weight

Weight	20 mg/kg	40 mg/kg	ml range at 300 mg/ml	100 mg/kg
3 kg	60 mg	120 mg	0.20-0.40 ml	300 mg, 1.0 ml
4 kg	80 mg	160 mg	0.27-0.53 ml	400 mg, 1.3 ml
5 kg	100 mg	200 mg	0.33-0.67 ml	500 mg, 1.7 ml
6 kg	120 mg	240 mg	0.40-0.80 ml	600 mg, 2.0 ml

Round down for a cat that has never had oil, round up only after 2 weeks of clean stools, and recalculate after any weight change above 5 percent.

• Weigh the cat and write the milligram target before opening the bottle.
• Add EPA and DHA from the label; ignore the total oil figure.
• Start at 25 to 50 percent of target for 5 to 7 days.
• Stop 7 to 10 days before surgery or a dental with extractions.
• Refrigerate after opening and discard at 90 days.

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