crazy delay/lag

Everything was fine in 1.6.4. I updated to 1.7.2 a few days ago, and all of a sudden, every time I breed chickens, I end up getting a crazy delay in the game speed, which stays for the rest of the game (even if I close, and relaunch minecraft). I only play in single player, and I do breed chickens in large numbers, which always causes some lag, but I've never had a delay like this.

For example, I'll be feeding them seeds, and running around the chicken pen, after a few seconds, I'll notice that they are actually surrounding me where I was a few seconds ago, not where I am now. The game gets delayed by a few seconds, and whatever action I do doesn't get done till later. After a while, this delay ends up being REALLY long, close to a minute, and stays with me, even after I leave the chickens. For example, if I try to open a chest with this delay, nothing happens. Then after about 30-45 seconds, I get the chest inventory on my screen (even if I've already left the chest). The same goes for doors, fence gates, riding horse, etc.

what do I do?