Camu camu powder is sold on amazon and is the highest form of natural non synthetic vitamin c than any other fruit on the planet. I give it to my dogs daily. Look up camu camu and its wonderful benefits. Just one teaspoon is 1,080 % of vitamin c.
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The vitamin C I used is a whole food type by Healthforce Nutritionals. It's a complete form of VC, not an isolate like ascorbic acid is so the body can make use of it without having to rob the body of rutin, bioflavonoids and such, to remake a complete, useable molecule.
My 2 yr old, 80 lb Dogo Argentino gets 325 mg 3 times a day to combat arthritis and chronic ear infections.
As an afterthought ~ vitamin C works in conjunction with other nutrients for it's activation. If you aren't doing a raw diet, where they get their calcium and magnesium (along with so many other nutrients) from eating raw bones, you should supplement. If you are using ascorbic acid or some other isolate form of vitamin c you should also supplement bioflavonoids.
Lastly, Steroids medication deplete vitamin C, so you'll need higher dosage till you wean off the drugs and heat destroys VC so don't do that :o)
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Carol; I use the powdered Ester C for my cats and dogs. The only thing it says on it is Ester C natural flavor/24 hour immune support, also explains all the positive results etc. Good Luck