As I am sure you are aware, if your dog has had kennel cough (infectious tracheobronchitis) for a few days he will be coughing a lot . This could result in small amounts of blood in the mucus that he coughs up as a result of the constant irritation and the bursting of tiny blood vessels in the membranes.

However, if you believe the amount of blood to be significant, or if there are any other symptoms such as fever of lack of appetite you need to take him to the vet either for a cough suppressant to relieve the symptoms or for a check up to ensure that further complications such a pneumonia have not developed.