Evidence for multigene control of cryptorchidism in swine

The mode of inheritance of cryptorchidism was investigated in Duroc swine. Matings of cryptorchid males with females whose full-sib brothers were cryptorchids were done. Sixteen of these litters were farrowed, and 54 males were born, of which 8 were cryptorchid. Two hypotheses were examined: first, that this trait is controlled by homozygosity of a recessive gene at a single locus; second, that it is controlled by homozygosity of recessive genes at two loci. The single-locus recessive hypothesis was rejected (P less than .01), but the two-locus model was not. Culling to reduce the incidence of cryptorchidism is discussed.