Ear infections in dogs
Many dogs, especially dogs with floppy ears, develop ear infections in their lifetime. Usually the causes for ear infections are moisture in the ear, either from the ear not breathing because the flap closes it or from swimming, and allergies, both food related and environmental.
The diagnosis of an ear infection at home is fairly simple. First, smell the ear. If the smell is very pungent, your dog is likely to have an infected ear. Second, look at the ear. If the ear has brown waxy dirt deposits inside, chances are the ear is infected. Third, when you massage the ear, the dog leans toward your massaging hand. Generally, the harder your dog leans, the more serious the ear infection. You may also notice your dog scratching his/her ears more frequently and shaking his/her head often as well.
The first ear infection requires a vet visit. Once there, the vet will likely flush out the ears and prescribe antibiotic/antifungal drops. You must follow his advice accurately to avoid the creation of resistant bacteria or yeast in the ears from improperly administering the drops. The vet might recommend that you return for another ear flushing once a week until the ears are clean enough to successfully fully treat the infection. These follow-up visits are usually free or at a substantially reduced rate, so don't be intimidated by them.
Once the ear infection is under control, your vet can show you how to properly clean the ears using an ear cleaning solution, such as Vet Solutions, Routeen and many others. Using these solutions while the ear is still raw from the infection is particularly painful and should be avoided. Dogs whose infected ears are cleaned with these alcohol-based solutions tend to become afraid of ear cleanings really quickly (it stings when the ears are seriously infected).
Now for the cause- the ears are clean and uninfected, but for how long? If the dog is no longer swimming, and moisture in the ear was the problem, the ear infection shouldn't return until the next swim. If the ears became infected because of allergies, they're likely to return quickly.
You can help in both situations by cleaning the dogs ears thoroughly after swimming and by cleaning the ears on a regular basis if you see they're getting progressively dirty.
In the case of allergies, the dirt in the ears will seem to accumulate faster than you can clean it. The first step in this case is an elimination diet. You take ALL the foods your dog has ever eaten and compare the labels. Then you find a new food without any of the same ingredients (except the vitamins and minerals). The less overlap in ingredients between the new food and the old foods, the better the chances are of your dog not being allergic to it.
So for example, if your dog is eating a chicken and rice food, the most obvious opposite is fish and potato. Generally, people will move to lamb and rice foods. Some can be ok, but in general, the basic lamb and rice foods have too much overlap with the basic chicken foods. That is why fish and potato is a better choice (among other reasons).
Be sure to switch foods very gradually. As your dog is having an allergic reaction, it is likely that his/her immune system has been compromised a little bit, so any reactions to a change of food might be amplified.
Once completely switched to a new food, watch your dog closely for changes. If the dog gets worse, or develops other serious symptoms, the food might not be the right choice. If the dog stays the same, or gets better, stay on the food for at least three months. Some allergies take months to heal up, regardless of the source being removed.
In the case of the dog getting worse or just never getting better on the new food, after seeing your vet to be sure everything is ok, you can try a further elimination diet or you can ask your vet for allergy tests, both environmental and food related. It is possible that your dog is allergic to multiple things, and an elimination diet will be just too hard to accomplish without knowing exactly what to avoid.