Breathing difficulties after amputation

Is your dog on any pain meds such as NSAIDs (non-steroidal anti-inflammatories)? They can sometimes cause dogs to pant excessively or have breathing problems. Does your dog have allergies? What is the reason your dog's leg was amputated? If it was due to cancer, a chest xray may be advised to rule out metastasis. In any case, your dog should be seen by a vet before the problem escalates.