I think for many the difference is "companion animals" vs "domesticated" because most of the livestock we have in the US are still considered domesticated animals. Dogs along with horses are considered "companion" (domesticated just like cattle, sheep, pigs, and horses, but a companion) animals and not eaten. (as a rule because just like the dogs in the pictures, I know horse meat is in high demand in other countries
and it makes me just as ill to think about eating horse meat.)