Animals that had visual input to one eye eliminated by a patch or by sewing the lid shut and patching it, failed to develop the ability to focus, developed strabismus and other visual impairments in that eye. Optic nerves connecting visual projection areas of the brain with visual cortex had no or far less than normal myelinization than in intact animals. The eye itself was complete in all respects and was normal size, but because of the effects on the nerve development, vision in the covered, unused eye was always drastically impaired.

The implication for the "use or lose" or, "use or it will never develop" on pups is that the more physically challenged the pup is the better the coordination. Environmental enrichment, to borrow a term from the animal care and welfare dictionary, means adding things to the rearing pen to provide objects that the pups (in our case) can manipulate, chew on, carry, climb onto, or over or around. These objects of enrichment provide the physical and mental challenges needed for young developing dog bodies and dog minds.

The wild canids, wolves, coyotes, foxes all provide pups with these challenges by selecting den sites with rocks, tree roots, down tree limbs, hilly and uneven ground around the entrance, or they move the pups at four or five weeks of age to a secondary den site that does provide it. For five years running there was an active fox den nearby that I could see each day as I drove to and from work. Each year the dog and vixen appeared in March. In April and May the dog fox brought food to the vixen in the den.

The den was an old renovated woodchuck burrow on a south-facing slope with weeds and grass typical of an old field in this part of the country. In late May the pups emerged from the den and could be seen playing or sunning at the mouth. Within a week the vixen moved everybody, troop and baggage, to a den about 100 yards south of the natal den. This rearing den was at the base of a fallen down rock fence with a few split rails lying on it. From then on until the pups were weaned and out hunting on their own, each day was play time games in the rock pile.

They used the rocks and split rails the way our kids use all the constructed apparatus we build for them in the playground. There in the rocks they developed the skills, strength, agility and coordination to catch a mouse or a rabbit or a ruffed grouse. The pups we raise need a similar physically and mentally challenging play ground to develop their muscle and brain power.

In the sterile four walls, wire or wood or cement block rearing kennels we use with only mom and the siblings, pups have nothing to use except each other to crawl over and hide behind. They still learn the stalk and pounce and the social amenities. But they are doing it in an aggressive, unimaginative way and, an aggressive, unimaginative dog is not what I want for a hunting dog. Pups need the physically challenging environment where they can develop muscle coordination, agility and strength. At least equally, or even more so, they need the mentally challenging environment.