Likely twice as old as written language. https://www.livescience.com/stone-age-dog-burial.html Abuse of a dog or cat is a crime against civilization itself.
I've made this argument many times and it always raises eyebrows and induces shrugs. We as a species co-evolved with some animals and not others. Our partnership with extends deep into the mists of pre-history. We and they have co-evolved to an extent to be better companions. Eating a dog is a profound betrayal unlike that of eating a horse. Come at me
Maybe when we were nomads and the dogs roamed around freely around the tribe.
But most dogs today are locked in, most of the time and when they get outside, they are on a leash. Totally dependant on their human masters.
I don't think I would describe that relationship as a partnership.
Then there is the concept of breeding them, to establish certain "cute" traits, but cause great pain and misery to the animal:
https://de.m.wikipedia.org/wiki/Qualzucht (german)
I would argue, the native american tribes, who also did eat their dogs, treated them better overall, than humanity does today on average. So many dogs bred for running around, are lucky today, if they get to walk around outside for more than 20 minutes. This I would call betrayal.