An average of 660,000 animals are killed each year for their meat. They will starve and die. They will be preyed upon and eaten by other creatures. Or, to spare them from that cruelty, we will just have to kill and put them out of their misery. No matter what we do, they will die, just as we eventually die.
Humans suffer all the time.
It is the nature of existence. In any case, they probably die much more humanely than if they were starving to death somewhere or being slowly killed by a pack of wolves. This argument is the biggest fallacy in the vegetarians arsenal. I know a lot of people with canines, some more pronounced than others. We all have them.