It sounds to me like he is coughing. Coughing can be from a variety of reasons including upper respiratory illnesses such as allergies, kennel cough, bronchitis and even inhaled allergies. Dogs from breeding kennels and pet stores often contract kennel cough. Even a reputable kennel can have cases of kennel cough. Your dog can even contract it from the vet's office. So you do have to consider that possibility. Let me give you information about these things first and then give you another possibility which is probably the cause. I like to go over all possibilities so you have the information and you might see something when you are reading the sites that helps pin down the cause.
You can read about bronchitis in dogs here:
If there is also sneezing and nasal congestion, it could be due to an allergic reaction to an inhaled substance. If this is the case, Benadryl can be given to your dog, the dose is up to 2mg per pound every 8 hours. You can read about these here.
Kennel cough is normally contracted when a dog has been boarded or kenneled or around a large number of dogs such as at a dog show, dog park or pet store. It is usually self limiting and lasts about 3 weeks but pups are prone to longer bouts since they are more susceptible to secondary bacterial infections. Here is a website with more information on kennel cough. http://www.peteducation.com/article.cfm?c=2+2096&aid=452
Canine influenza is now becoming more prevalent and like it sounds it is a canine flu. Here is an excellent site on it.
You will want to monitor your dogs condition looking for colored discharge from the nose or eyes, a productive cough (coughs stuff up), stops eating or lethargy. These are signs of a possible bacterial infection as well and my require antibiotics. If your dog appears to be having a difficult time breathing, you will need to see your Vet as some dogs dog get really sick with canine influenza and need support to recover.
To help your dog breathe easier you can run a NON-medicated humidifier in the room your dog is in, or sit in a steamed up bathroom with your dog to help keep the mucous moving. Robitussin DM at a 1/4 teaspoon per 5 pounds can be used to control the cough. It should only contain dextromethorphan and Guaifenisen. and should NOT contain pseudoephedrine. Dosages can be obtained at this website. http://www.petplace.com/drug-library/dextromethorphan-robitussin-dm/page1.aspx
There are other reasons for coughs such as heart problems which should be investigated if your dog is not on heartworm preventative or is an older dog. The following site goes over canine coughs.
Now I mentioned other possibilities and those would include reverse sneezes and collapsing trachea as well as problems associated with Brachycephalic breeds like the french bulldog. Here is a site on reverse sneezes and one on collapsing tracheas.
Collapsing tracheas and reverse sneezing is common and usually not life threatening. Owners report stroking the throat lessens the length and severity of incidents of collapsing tracheas.
What is likely to be the cause though is problems associated with Brachycephalic airway syndrome. These issues can include narrow nares and elongated palete. The elongated palate often will obstruct the airway and lead to a dog coughing or gagging. Read more on this here.
This is a common problem in your breed and you should have him checked over by your vet at his next appointment. If he is having any difficulties breathing, I would have him checked over sooner.
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