Umbilical hernia, in which a bit of intestine or omentum protrudes through the abdominal wall without any rupture of the skin, can be attributed to failure of the umbilical ring to close. The condition is found in several species of mammals, and dogs are not exempt.
In a review of the cases reported in several species by a number ofveterinary hospitals, Hayes (1974) had 382 cases in dogs, with forty-five different breeds represented in the group. His analysis indicated somewhat higher risk of umbilical hernia in the Airedale Terrier, Basenji, Pekingese, Pointer, and Weimaraner. It must be remembered, however, that these calculations were based on the numbers of dogs in the hospitals, and that, while such records for several hospitals can yield large numbers, one may well question whether or not they provide adequate samples of the breeds.
Umbilical hernia in Cocker Spaniels was studied by Phillips and Felton (1939). It appeared within five weeks of birth, was usually small, and sometimes disappeared soon after weaning. Those hernias that persisted in adults became proportionately smaller than in the puppies. In one kennel, parents both normal yielded offspring (nine litters) among which about a third showed hernia, but, among 10 puppies from parents both herniated, 6 showed the trait. Phillips and Felton concluded that susceptibility to the condition is genetic, recessive, polygenic, and independent of sex and color.
Experimental investigations to demonstrate a genetic basis for umbilical hernia in dogs are not necessary. Enough evidence has been provided from studies with cattle and rats to prove that the underlying weakness is hereditary in those species. It is likely to be the same in other mammals. Moore and Schaible (1936) selected for hernia in their rats and raised its frequency from an initial 2.7 percent to 71.2 percent. Moreover, they ended up with hernias far bigger and better than the little ones with which they had started selection.
The message for dog breeders seems clear. Don't breed from any animals with umbilical hernia-or from one in which the defect has been surgically "corrected." Eliminate it by progeny-testing, as with any other polygenic trait.
With inguinal hernia, loops of the intestine descend through the inguinal canal into the scrotum. The survey by Hayes turned up 88 cases in several breeds. Among those with a comparatively high incidence was the Basenji, which Fox (1963) had previously found susceptible to the defect. Others with risk above average were the Basset Hound, Cairn Terrier, Pekingese, and West Highland White Terrier. Crossbreds had a relatively low risk. By selection for inguinal hernia in swine, Warwick(1931) raised its frequency from 1.7 percent in the original unselected stock to 90 percent in only six generations. Further warning to dog breeders seems unnecessary.