From http://dev.bukkit.org/bukkit-plugins/fun-hard-mode/tickets/117-realistic-animal-farming/

Reported by WoodenAxeServer:

Animals should not spawn/breed or should die if they are packed into too small of an area. People tend to make cow/chicken grinders where there's 100 cows packed into in a single block space. There could be a configurable "animal density" where animals start dieing if they are over that density in an area.

Diemex:

I have planned this feature for quite some time but have never gotten around to it.

Details are on this trello board: https://trello.com/b/MP0MX9wf/bukkit-animal-breeding-overhaul

pilvimaa:
This would be so. Awesome. It's been bothering me for a long while that people have these horrible meat grinders in a very small area. There have also been cases where the area has become unplayable because of the severe slowdowns caused by all those animals.

Sounds simple enough to implement. Remember to deny drops for animals killed in this fashion.

EDIT: Oh, I didn't read the link you provided at first. I thought you would perform simple area checks. But this is very... elaborate. I don't like the old age part with potion effects but the requirement that animals have to eat sounds very interesting.