My name is ***** ***** I’ve been involved professionally with dogs in the health and behavioral fields for over 18 years. It will be my pleasure to work with you today.
Coughs can occur for quite a few reasons. They can develop upper respiratory illnesses such as kennel cough and canine influenza as well as bronchitis and inhaled allergies. You can read about bronchitis here:
If your dog is sneezing and has nasal congestion, then 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. 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 more widespread than it has been in the past and like it sounds it is a canine flu. Here is an excellent site on it.
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.
I'm pretty sure you know about reverse sneezing and collapsing tracheas since your boy is 9 years old and these are common issues, but let me give you some sites that discuss this.
What concerns me though is that you describe it as a breathy cough and you believe his belly is a bit distended. This might point to a heart issue. With congestive heart failure there can be fluid retention in the abdomen. Read more on this here:
I strongly suggest you have him seen by your vet as soon as possible and I'd keep him inactive until then as well. I hope this information is helpful to you. If you would like any additional information or have more questions please don’t hesitate to press the reply to expert or continue conversation button so I can address any issues you still have . If you do find this helpful, please take this opportunity to rate my answer positively so I am compensated for my time.