Eh... for S&G try the MSM and add in some Coconut oil too - it's not going to hurt anything, it's relatively cheap, both also aid with digestion, not just skin, and if it doesn't work, your other dogs will love it. Hell, if you get human grade MSM instead of feed store stuff, you can take it, and the coconut oil makes for awesome stir fries.
"We become better trainers by refusing to swallow uncritically what is tossed to us as truth,
by developing our powers of empathy and observation,
and by searching for better ways to teach and educate the dogs we love."