Prescription dog food abbreviations:

I/D-Digestive health
J/D-Joint health
L/D-Liver problems
N/D-Cancer
R/D-Weight control
T/D-Gum disease and tooth care
W/D-Diabetes
Z/D-Food allergies

From this link: http://www.vetinfo.com/veterinarian-prescription-dog-food.html

d/d appears to be for skin issues:

http://www.hillspet.com/products/pd-cani...ormula-dry.html