kate negus do really nice rubber reins they might be the suregrip ones i cant remember anyway i have the thinner ones and they are perfect and my husband has the normal ones and they feel so big after using my smaller ones!
assuming your vet has had a look to make sure its nothing serious.....make sure the shetland can always move so dont keep in a stable. walking in hand to help build up the muscles. of course not over doing it at a young age....
agree they are really nice rugs but if you have a horse that rubs it will destroy the rug. and unless you have the neck attached to a headcollar or fly mask it doesnt sit up very well. but i do think they fit very well over the shoulders and sit nicely over their bum!