My dog Zuul, a Cavalier King Charles Spaniel, has a frizzy coat. I've been feeding her salmon oil to help make it more manageable.
Zuul's hair is inexplicably frizzy. She drags home every branch and foxtail that comes near her, and brushing it all out is a pain. Our vet was unable to find any "problems" that'd be causing Zuulie to floof the heck out, and suggested I try changing her diet around. I'm about 60 days into salmon oil, and it is making some differences.
I've tried lots of coat improving additives in the past, The Missing Link being a favorite. Nemo, my Great Pyrenees, coat looks amazing, always, but after a few weeks of regular Missing Link dosages, he is far less shedding and even softer. Missing Link, however, didn't help Zuul. Her fur was just as cotton-ball-esque as ever.
I have enjoyed some luck in the past with salmon oil. The Zuul and Nemo both love it squirted on their food, but a woman I was spending a lot of time with complained their breath became less pleasant. She is long gone, but the dogs are here to stay. I bought a jug.
A simple squirt in her food bowl once a day is all it takes. After about 60 days, or two containers of oil, I've found that Zuul has become a lot easier to brush. She tangles less, mats form more slowly, and her breath smells a bit fishy sometimes.
Pure Wild Alaskan Salmon Oil for Dogs & Cats via Amazon