I have a pasture with a long 3' culvert running into it.  The previous owner had it barricaded but the boards washed out one time and it didn't take long and we had lots of calves outside the fence.  Of course, they couldn't  find there way back in, so the barrier was promptly fixed.  

On a related note, the county installed 4' cement culverts for use as a sheep pass by our yard, and the damn sheep shouldn't go through there no way, no how.  We finally had to fence an alley way from the barn/corral down to the pass, so they had nowhere else to graze.  Now they use it just fine.  If they aren't supposed to go through, then they go through with no problems.