Many cases of injuries of neck tissues of dogs have been linked to the use of a collar and leash. Respiratory problems, swallowing difficulties, as well as swelling of the area around the throat can also be caused by a tight collar or when a dog pulls hard on his collar and leash during walks. Continued use may possibly lead to more serious injuries and even death. There have been many cases of deaths in dogs caused by choking on their own collars.
A dog that constantly chokes on his collar during walks won’t enjoy outdoor excursions. Instead of getting excited once he sees you get his collar and leash, he will try to get away or may refuse to wear them.
Using a harness in lieu of a collar is the best answer to your dog’s problem. He may resist your efforts when you try to fit his new harness. Bribing him with his favorite treats will certainly make him more accommodating of your efforts. Make sure to do this during the first few times of putting on the harness, until he becomes used wearing it and looks forward to your daily walks.
Source: Importance of a Dog Harness