Hi, I'm Dr. Peter. Welcome to JustAnswer. I'm reviewing your question now, and will post back with your reply ASAP.
Welcome and thanks for asking your question. My name is***** am a licensed veterinarian. I am sorry for the delay in response. If you would like to continue can you please answer a few questions so that I can be well informed and give you the best advice.
1- Is he hacking/gagging like if something is stuck in the throat?
2- Is he doing this at home when not walking?
3- Do you walk him with a harness or collar?
4- Any pre existing medical conditions?
5- How long has this been going on?There may be a slight delay between your follow ups and my replies as I type out a thorough reply for you.
Thank you for answering my questions. Please give me 5-10 minutes to type your answer.
Friend, when a dog is hacking/gagging this is likely a sign of inflammation in the upper airway. A very common cause is an upper respiratory infection, basically a dog cold. Another common cause is a collapsing trachea, this is when the rings around the trachea become weak and collapse, the patient will then gag/hack to re-open the trachea lumen. The fact that this is happening mainly during his walk I am inclined to believe this is related to a cold. You see even though the collar is loose when it rubs against the neck this will cause hacking by stimulating the trachea (tube connecting mouth to lungs).
I would recommend a hands-on examination with your family veterinarian to auscultate his heart and lungs to make sure sounds are clear. In addition, he may need oral antibiotics. In the meantime, you can start him on Robitussin DM (cough) 1/2 teaspoon every 6-8 hours. You can buy Robitussin DM (cough) over the counter in any pharmacy. Do not buy sugar-free. Finally, I would stop using the collar and switch him over to a harness until this resolves.
My goal is to provide you with excellent service - I hope I've provided the information you were seeking, if you feel you have received anything less, please reply back as I am happy to address follow-up questions. Kindly rate me when you are done.
You're welcome. :)