I just went thru an epidemic of kennel cough with my 3 dogs and here is what happened.
I have 2 rescues (ages 5 and 7) and 8 month puppy. The 5 yo raw fed (1 1/2 years) rescue who was severely neglected/emaciated when I got him 2 years ago was only mildly sick 1 1/2 days with KC. He had no current bordatella shot
The 7 yo who was up-to-date with the vaccine - was very sick for 7 days. and of course the puppy is/was very sick inspite of her vaccine. These 2 dogs are kibble/canned/some cooked meat..
The raw -fed boy only coughed 3 times (that I heard) compared to 100's the other boy coughed.
I was so pleasantly surprised when the raw-fed boy was fine the next day. It jsut made me realize he has recovered and his immune system is strong.
Now maybe this is no accurate comparision becuase the sick boy and pup are bulldogs and the raw boy is a Golden mix . But I think its a good thing and the puppy will be raw fed soon too. (if she ever smells raw, she is a nutcase- she gets it once in a while and races to the Goldens bowl to lick the leftovers).
The supplements all dogs got were fish oil, Vit E daily. The Golden got Seameal and Canine One sporadicly. The old bulldog got Nupro at the foster moms for a year. The puppy had been on Echanacia, Colestrum, Vit A, E, C for mange last month (her immune system is so compromised it was a given for her to get KC).