Collars and harnesses serve different purposes. A collar is simple for identification and light everyday use, while a well-fitted harness distributes lead pressure over a larger area of the body.
When a collar can be practical
For dogs that walk calmly and comfortably, a correctly fitted collar can be convenient. You should be able to check the fit regularly and ensure it is not too tight or loose.
When a harness may help
A harness can offer more control and may be useful for dogs that pull, have a narrow head, or need a more secure walking setup. Fit matters: straps should not rub the armpits or restrict shoulder movement.
For breathing, neck, back or mobility concerns, ask a veterinarian or qualified professional which setup is appropriate for your dog.