For happy piggies don't just pet and nibble give them a grain or two to prevent them from starving. They are beginning to disappear from the streets and some of that will be because of the quest to catch them but some will be due to starvation.
For new players - feed them 3 of anything you can grow from seeds and they will reward you with a piggy plop which you can examine to find a seed of whatever you fed them.
For instant revitalization if they are telling you they have no meat to give you can also feed them one meat.
Feed the piggies, love the piggies, keep the piggy population healthy!