My maine coon cat has Dandruff?

Your cat has likely had dandruff for awhile, just not very noticeable with the longer fur. It can often be cured with a better quality diet. Look at the ingredients on your cat's food bag. If you see corn, wheat, or by-products, your cat would likely benefit from something better. Grain free or a canned food are generally the best options. You can also add fish oil to his diet, either from the pet store or you can use the capsules for humans. If you use the capsules for humans, poke a hole in the end and squeeze perhaps half of it onto his food daily.