Kennel cough, usually makes them cough in quite a nasty way, but can looke different in different dogs too, so it is hard to rule out. I take it he does not have bordatella vaccination???
One thing I went through with a couple of my danes, and from what several breeders and vets told me is not too uncommon with danes is tonsillitis. Mostly they get it when they are rather young, and it can bring other unwanted side effects, I first realized a girl I had, had problems when she all of a sudden started to chew on the legs of my kitchen chairs. We brought her in after her breeder told me that it could be tonsillitis. She was right, that was what it was, she was on antibiotic for 7 days I think it was, she never got it again. The other dane I had that had problems with it, we had to remove them, he kept having problems so the vet suggested it. It can have different signs, chewing, drinking more, coughing, and like you say sounding like they have a sore throat, slime more.
I am sure it could also be a simple cold, if it is kennel cough you may be lucky and it goes away by itself, I am a little bit of a mama hen though, so I would probably take a trip to the vet. And with tonsillitis you will most definately need antib.
As for the kennel cough, I have all my dogs vaccinated, since I bring them everywhere and they meet so many other dogs. A couple of years ago when they had to give it in the nose, the dogs were not very impressed at all hehe, but now they have a regular shot for it and they give it when they give yearly boosters for all the other stuff, and I think I pay no more than 15 or so dollars for the bordatella.
I really hope Dane is feeling better soon, and please let us know how things go. Big slobbers to him and his little sister
Marit