I've read that it is recommended to give Omega-3 to elderly dogs (especially ones with arthritis) (for example, here).
My dog is a 15 years old female medium sized, mixed breed (probably mostly German Shepherd), weighing approximately 25 kg (55 lbs).
My questions are:
I can't say specifically what an appropriate omega 3 dose is for a dog. But what we've been doing with our dog is just buying cans of oily fish like sardines, and using them to 'top' her normal food. About a third of a tin for each meal (twice daily) for our 25kg mongrel. Definitely makes her food more attractive, and also gives here an assortment of useful fish oils.
We do notice the side effects after a few days - her coat becomes noticably a bit more water/mud resistant, and generally a bit more glossy and smooth.
In general, I prefer a natural source to a supplement, since it's both cheaper and easier to feed, and has a bit more a mix of nutrients.
I give my dog whatever fish-oil supplement I happen to be taking at the time. As far as drugs and medicines go, if it's human quality, it's ok for dogs. THE REVERSE IS NOT TRUE.
I poke the gel-cap with a push pin and squirt it in her food when I give her her daily food scoop. She seems to like to try to lick it up!
As far as dosage:
From http://www.petmd.com/blogs/thedailyvet/ktudor/2013/aug/the-dangers-of-too-much-fish-oil-30731
"The National Research Council has established a safe upper limit of EPA and DHA for dogs. It has yet to establish one for cats. In light of that, it is probably safe to use the guidelines for dogs for both species. Translating the data suggests that a dose between 20-55mg combined EPA and DHA per pound of body weight is safe for dogs and cats. This dose is far less than those used to treat serious conditions where the risk of side effects is less important than the benefits of treatment. Consult with your veterinarian when treating conditions requiring higher dosages."
When in doubt, just ask the vet.
