Anybody know anything about horses?

I was actually wondering where they even got so many horses to begin with.

As for Jerry's size - how does one even stay fat in an apocalypse? There is barely enough food to go around, certainly never enough to maintain that sort of body mass.

Walking should be no problem. You've heard the expression "strong as a horse" ... there is a reason for that. Horse are very cool.

Jerry weighs what 300-350? That's well within safe limit for a full grown horse.

Whoever played Rick's horse in the previous episode should get an Emmy. That horse had incredible range, showing fear and concern, but also loyalty to stick around and be able to save Rick. And when it came time to disappear into the woods, only a master could do that.