My cousins german shepherd is due pups in a couple of weeks, they have been looking at whelping boxes but we don't know what the pig rails are for and if you really need them. This mating was accidental so I have ordered book of the bitch to get all the information. She mated with their other german shepherd they managed to tie 2 times (read the other message with the akitas) no chance of getting them apart when she was ready he wasn't interested in her before then she thought it would be ok. If anyone can help I'd be grateful.

Pig rails are a rail around the lower edge of the whelping box, a few inches in and a few inches up that are supposed to prevent the bitch squashing a pup against the corners or edges of the box - they are only good for the first few days for, as soon as the pups become active and start to climb up the bitch they can get squashed between the rail and the bitch.  I use a 4" x 3" crate for my bitches to whelp in and line it with large cardboard boxes which I tie into place.  I use a couple of broom handles as pig rails and also make holes in the corners so I can tie the fleece down so the pups cannot get underneath it.

If you use skirting board or wooden planks about 4" x 1" screwed to the sides of the whelping box about 4" from the floor (so they stick out like a shelf into the box), then the pups can't get stuck between the rail and the wall of the whelping box.  But this only works if you have a wooden box - the new disposable cardboard ones obviously won't take the screws to fix the wood.

It does mean that you can leave the pig rail in place a little longer, but by about 2 - 3 weeks they can be removed.