why does my dog cough?

Question
My 10 year old collie  cross Jake has a bad cough at night and has earache, he has had this since we lost our 13 year old dog Kim, we have been to the vet on numerous ocassions and he says his Heart is fine and believes it could be an allegy, my 13 year old died with a bad Heart valve and she coughed in a simlar way, the vet gave Jake an injection each time an that clears up both earache and cough within a day and stay good for other a week, we have tried Jake on a diet of Minced beef and rice suggested by the vet which possibly helped but he gained 1kg in a month he is already over wieght.
Do you please have any possible diagnosis or treatment or diet ideas?
thankyou

Answer
I would recommend that you have chest x-rays taken of Jake to evaluate his lungs and heart.

If he is overweight, then losing weight will definitely help his overall health.  I would try to substitute green beans and carrots in his diet and feed a commercial LOW-Calorie food instead of the beef and rice to ensure he is getting the proper balance of vitamins and minerals.

If he has not had any blood testing, I would recommend having a CBC, Chem and T4 checked to rule out any underlying problems there.

I am not sure what injection is being given, but my guess is steroids (anti-inflammatory) which could indeed suggest that your dog has allergies and underling allergic bronchitis.  You could try giving Benadryl, 25 mg, three times a day to see if that helps.