The VERY best supplement for any dog is DOGtor X Formula. It is a completely natural product which contains every single vitamin, trace element, etc. etc. a dog needs to either remain healthy right through their lives, or if as with my older boy, works wonders on dis-eases.
Zeus, my older boy has Cushings Disease, He was a mess, it comes on very quickly. Coat was terrible, all red and blotchy, falling out (he was an Ashley & Martin candidate of the first order). This dis-ease also caused urinary tract problems like incontinence, bowel problems (every five minutes or so it seems need to 'go') excess water consumption, raving, crazy for food, weak hind legs and sway back. My boy couldn't even get up, he kinda shuffled along on his front paws 'bumping' to get his hind legs up. Plus the shakes, like he had the D.T's Very expensive vet's medication, blood tests etc. and not much improvement. A little at first but then all the symptoms came back, with avengence!
On DOGtor X Formula I saw an IMMEDIATE improvement the very next day! Now you'd never know he was actually suffering from Cushings. And he's almost 12 years old. He can now walk and walk, run and play with my youngster and all the other symptoms have vanished!!!!!!!!!!!!!!! His coat has NEVER been better. It's softer and silkier than it's ever been pre Cushings!
http://www.petequinox.com.au/test.html This is the Australian site, and you'll see Zeus' testimonial up first, but the formula is available world wide.
Also, I now have Ra Kismet (my youngster) on it, as it's so good for young dogs too. His coat gleams and as he's very energetic, he puts a lot of strain on his legs, mad soccer player

. So all round it's the VERY BEST doggy nutrition on the market.
It costs AU$69.95 per bottle. In tablet form and the dog's LOVE it!!!!!!!! They think it's a 'high value treat' and yes, I've actually used it as same!
Layla would only need one tablet per day, so the bottle would last around two/three months. Cost wise it's well worth it for a happy, healthy dog. Saves big vet bills, especially later in life.