Call your vet if you notice: 1  Persistent cough that disrupts sleep or lasts more than 24 hours. 2  Persistent nasal discharge, especially with mucus or blood. 3  A honking cough.  Wheezing or noisy 1  breathing. Persistent gagging.  Labored 1  breathing. If your dog is struggling to breathe, check the color of the gums and tongue. They should be  pink.