It's apparently somewhat of a private joke, due to the fact that the next show on the air was by the same creator:
In the closing moments of last night's Family Guy Peter Griffin introduced American Dad as "whatever Fox is limping to the barn with."
So, he means “whatever crap will air after this”, but is just humorous self-deprecation.
“Limping to the barn” is then understood as meaning “being of inferior quality”, or “performing badly”, or “tired”… A horse that limps back to the barn has been beaten, or is simply not in good shape altogether. I haven't heard this expression before, though… Other uses found by a web search include:
- Don't lie, by this time on this Thursday you're just limping to the barn at work.
- The running game will be "limping to the barn" at best this week.