Your whelping box should be about 75% longer than your brood-bitch when she's laying at full stretch. The sides of the whelping box should be about as high as your broody is, when she's standing.
You need a door, or lower section, in one side, so that she can step out easily, but this door should be high enough that the puppies can't accidently crawl out.
Heating the whelping box
The whelping box can have thermostatically controlled heating either in or under the floor... and there are whelping boxes like this made commercially, which are very strongly made and perfectly safe.
Alternatively a loose heating pad may be used to heat the box. These are also quite robust, and quite servicable.
An overhaed heating lamp is the cheapest way of heating the whelping box, but it is important to put carpet under the puppies in this case. This is because the floor of the box will be quite cold in the cooler months of the year.
Building the Whelping Box
If your brood bitch is going to whelp a litter of puppies, you need to have a whelping box.
A whelping box will help keep the puppies in one place, and minimize mess, both during and after whelping. The puppies will live exclusively in this box for about 3 weeks following whelping. Although they will be moved to an outside kennel area at about 4 to 5 weeks of age, depending on the weather, and they may still use the box as their bed, if they have access to it.
The size of your whelping box will depend on the size of your breed of dog. For example a greyhound will require a box about 4 feet by 4 feet square. It will need sides 12 to 18 inches high, with 12 inches minimum. A hard impervious floor, preferably made of wood. The floor should be at least 4 inches above any concrete flooring, to minimize heat loss through the bottom.
I’m going to go the through construction of a whelping box for a greyhound, which is a medium to large breed of dog.
A female greyhound stands about 25 - 27 inches at the withers (shoulder) and weighs about 25 - 30 kgs (55 - 66 lb’s), although a pregnant greyhound will obviously be heavier.
Materials you will need
Sides and door:
1 x 5/8” thick plywood board 48” x 96”
4” x 1” wood strips x 16’
2” x 1” wood strips x 8’
3 x 2” hinges with non-removable pins
2 x 2” gate hook and eye
1½” long wood screws
A Circular saw
4 x 3” mending braces
Sandpaper as needed
1 plywood board 4’ x 4’ - 5/8” - 1” thick
8 x 2” “L” shaped corner braces
Self adhesive Vinyl flooring material 4’ x 4’
Putting It All Together
Get the large sheet of plywood (48” x 96”) and cut it into 5 sections as follows:
2 pieces 12” x 48” each (sections A and B)
3 pieces 24” x 48” each (sections C,D and E)
Use a pencil or marker to name each section with a A, B... etc
Your 1st task is to build a folding door for your whelping box:
Take pieces A & B (12” x 48”) and lie them side by side so that the 48” edges are lined up. Join them with 3 hinges. Place one hinge about 10” from one end and repeat on the other end. Place a final hinge in the center. You should now have a 24” x 48” board, in which the top half can be folded down
Now apply the gait hook eyes to the top section. Place one eye through the edge of the board, through the thickness of the board (not on the same surface as the hinges). The eye should stick out of the edge of the board. Repeat on the other side. Make sure that the hinges are placed so that they are on the outside of the box and allow the top half of the door to fold away from the box
Your second task is to build the whelping box:
Cut your piece of 1” x 2” into 4 pieces, each 24” long
Take pieces C & D (24” x 48”) These will be the sides. On each 24” edge, secure a 1” x 2” wood strip on the inside of the box with 1½” wood screws.
The fourth piece (E) will be the back of the whelping box. Attach your last 24” x 48” (E) to sections © and (D), using 1½” wood screws. The screws should go from the outside of the box into the wood strips. 3 to 4 screws on each side should be enough. For a neat job, countersink them first. Make sure they don’t protrude through the wood strip inside the box.
Attach the front of the box, which is the door you assembled in step 1, using 3 to 4 screws on each side. Only attach the bottom half of the door. The upper half will be the swinging door. Make sure the gait hook eyes are on the upper half.
Apply the gait hook on the upper front corner of sides C and D. Be sure it coincides with the eyes previously placed on the front of the door.
All four walls of your whelping box are now attached.
The floor is easily attached by inverting your whelping box, and screwing F, the 48” x 48” piece of ply on. Screw the floor (F) into the 1” x 2” wood strips on the four edges of sections C and D. You can reinforce this if you wish, by applying “L” shaped corner braces between the whelping box floor and sides, but it should not be necessary. Two braces per side should be sufficient to secure the floor.
Now smooth out any rough surfaces and edges with sandpaper.
Finishing The Job
To help protect the puppies from being crushed by their mother you can build what is referred to as a puppy rail around the inside of the Whelping Box. The idea is that when the bitch lays against the wall or corners of the box, she can't squash the puppies, because they are under the anti-crush rail.
Fix 2 pieces of 48" long 4" x 1" wood strips along both sides of the whelping box, about 5 or 6 inches above the floor. Screw them securely at both ends and in the middle. Now take 2 strips of 40" x 4" x 1" and secure front and back, so they meet up with the 48" long strips. You could secure them together at the corners with triangular brace's made from left over ply wood if you wish.
Finally, you can attach the 48" x 48" piece of vinyl to the floor with a strong flooring glue. This will make it easy to clean, and keep the wooden floor from getting soaked with urine.
Absorbant Whelping Matt
There are some very good quality absorbant matts available, that are ideal to use as floor coverings in the whelping box. The polyester, rubber-backed and absorbant Steri-lon Pad is ideal. It comes in rolls of 15 or 30 feet.
Just cut it into 47" long pieces and secure to the whelping box floor with tacks. When it becomes soiled, it's easy to take out for cleaning, and replace with a new piece. With 3 or 4 pieces cut to size, you will alway's have a clean, dry and hygenic, whelping matt under the puppies.