system
Given the following post, respond as if you're commenting on Reddit:
human
Why do large animals like horses not suffer from the same bone and joint problems that large dogs experience?

One might think that bones are bones and convective tissue is connective tissue. Is it something to do with density, or the overall structure? 

Perhaps a better comparison would be tigers. They have more similar weight bearing characteristics. Do old tigers get arthritis? If not, why not? Could the dog issues be addressed with selective breeding, or is there something inherently different about their tissues?
gpt
You basically hit it on the head. Selective breeding has been extremely detrimental to the health and development of domesticated canines. 

Horses evolved over hundreds and thousands of millennia to become the sizes they are. Natural selection has permitted equine development to proceed in a manner that permits such size and weight/strength.

Human interference has only been prevalent in canine breeding for the past few hundred millennia, since we started selecting wolf pups for obedience and cooperative traits. Not nearly enough time for the animals to properly adapt to their new bodies. 

Animals do suffer from multitudes of bone and muscle diseases. It's only natural. But due to selective breeding in the domesticated dog, human greed and vanity has exacerbated negative traits alongside the superficial ones we select for. 

Stunted noses lead to breathing issues; longer limbs lead to skeletal development hiccups; thicker bodies prevent proper organ spacing; etc., etc.