Also dig a deeper perimeter on the outer edge of your apron(more concrete), that adds strenght when the cattle create the mud hole behind the edge of the concrete and "walk" the dirt away. With the added strenght, you shouldn't break the edge of the concrete when you drive the tractor/loader and manure spreader "off the edge" while you are cleaning up the yard, then putting in more dirt to fix the mudhole/edge up again.

Dad has done this and works very well, to save the edges. [4" slab probably has 8-10" depth and wide perimeter at edge of concrete.]

Edit: Sorry, M Thomas; Didn't mean to reply under your reply. My mistake.