Small Animal Review: March 2021

The danger of inbreeding has long been recognised. While it can be a useful technique for breeders to concentrate desirable traits, such as coat colour or limb length, within a breed and help offspring to be “true” to their parents’ characteristics, it can narrow the gene pool, leading to a concentration of deleterious characteristics. Some of these problems can be a result of the intentional characteristics introduced into the breed (such as flat noses associated with brachycephalic airway syndrome, entropion associated with selection of cosmetically desirable eyelid conformations, or skin fold pyoderma associated with the appearance of the snouts of various breeds), but some are clustered in breeds simply by virtue of being linked by chance to desirable characteristics. For example, while Chiari malformation and syringomyelia in Cavalier King Charles Spaniels are associated with the desire to breed a particular skull shape, myxomatous degeneration of the mitral valve in this breed is not a consequence of a purposeful selection. Rather, this stems from a narrow gene pool in which deleterious recessive genes, (normally harmless in a genetically diverse population because of the presence of dominant genes), are concentrated.