This appears to be the case in sheep and some breeds of pigs, while in goats and other pig breeds there appear to be at least two pairs of autosomal recessive genes involved. In dogs, both multiple gene involvement and incomplete penetrance have been suggested as genetic models. Until more data has been collected and examined, the exact mechanism will remain uncertain. As the cause of the problem is also inconstant, different causes may have different genetics. In rats, cryptorchidism can be induced by feeding diets deficient in Vitamin A or biotin, while testicular migration is delayed in animals fed folic acid deficient diets.
Dietary deficiency is unlikely to be a cause of the problem in our Beardies, however.
There is some debate as to when a dog should be classified as cryptorchid. It is agreed that a dog with only one or no scrotal testicles at the age of 6 months is affected. Many veterinarians feel that a dog should be so classified if he hasn't got two descended at eight weeks of age. Given that testicular palpation is something of a fine art, it is possible to miss one at that age, particularly in smaller or fatter puppies. I don't even begin to look for testicles until the puppies are six weeks old.