Most dogs are lactose intollerant (same as some people) and when given in excess amounts, milk can cause a loose stool or diarrhea. Lactose-free milk would be fine. The also have lactose-free ice cream which my dogs enjoy on occasion in the summer!
Well what else is new,Schoolbus gal has an opposing point of view. I give my mature dogs milk all the time. They love it and have no problems with it. Same for ice cream and the dreaded chocolate. Now before any of you start on me, I don't sit there and load them up on it, but I do let them have it. If they were to have a problem, of course i would not give it to them. I use evaported milk to help put weight on a skinny dog......Oh well...my advice to people always is this: try it and if it works for you,go for it.