Your dog's sense of hearing can be impaired by a variety of health problems. These include congenital deficit, age-related damage, outer- and middle-ear infections, and drug and lead toxicity. 

To maintain your dog's hearing, seek treatment for ear infections, adhere closely to your veterinarian's instructions for drug dosing, and do not expose your dog to lead or excessively loud noises.

If you suspect your dog has a hearing loss, seek veterinary attention. After ruling out underlying conditions that may impair hearing, your veterinarian may order a BAER (brain stem auditory evoked response) test to check your dog's a uditory pathways.