[DreamsComeTrue]

Maybe it's their food?

Have you tried the Super Cream Coat Conditioner from Bio-Groom? They have directions for mixing it to make a hot oil treatment and several other ways of using it. For dry damaged coat -

"For severely dry and damaged coat, apply Super Cream (full strength) to skin and coat. Wrap pet in warm towels. Keep pet in an area where conditioner will not be transferred to furniture or carpet, preferably a kennel or bathroom. Re-warm and reapply the towels several times while the conditioner remains on pet, up to 6 hours. Follow by bathing the pet in Bio-Groom shampoo (I personally would suggest the Protein Lanolin shampoo). Rinse and towel dry. Repeat as needed until coat is revived."