We started using a prong collar about a month ago. The first week was great. Bailey became a dream to walk particularly since both my husband and son had refused to walk her due to her pulling. I was afraid of falling, so this was a blessing, especially with my age and the worsening weather conditions.
At any rate, everything was fine, then suddenly she became ill. She was drooling uncontrollably....it was just pouring out of her. Her muzzle was so wet, and I was terribly afraid. Then she had diarrhea and whitish loose poops. I took her to the vet and he agreed with members if the Forum that the first place to start was remove the collar. He followed up with a probiotic therapy. Then it was wait and pray. Within three days the uncontrolled drooling had stopped. Her muzzle was dry. Her stomach settled down. Within a week everything was normal.
We don't know the cause, however, we have increased the links in the prong and we are reintroducing it, but, optionally. Was it a pinched nerve? Was the excessive salivation and swallowing upsetting her system? We don't know. She hates the prong, but we are putting it on her and hooking up to her flat collar...If she's out of hand, we can switch to the prong for control. Bailey will learn, it's up to her, pain or pleasure. If she listens and obeys, no prong. She's smart, she'll get the drift and behave on walks.
As long as you consider your dog's health and welfare, and you keep your eyes open for any distress, it is a valuable tool.