I have been fighting this problem with Mandie. For the most part, her hair has gotten better but she is still dry and frizzy along the spine.
Coconut oil (Nutiva is what I get) is a good supplement. (if you feed only kibble, it helps to give a dab of oil..not much though due to pancreatic issues. I give her about 1/4 to 1/2 tbsp a day)
I also started putting Argan oil products on her. I'm trying various ones. Right now, I use a leave in conditioner that has it as one of the top 4 or 5 ingredients.
I just ordered some Halo Dreamcoat. Another member (Carmen - mom to Luma) recommended this as it has helped Luma's coat.
AND, I'm testing various conditioners at bath time. I just received the hair restore by Espree (I ordered from Jenny at
http://toplinepet.com ). *she also sent me something to try that was from her own stash. I will let you know if it works)