Estimates of genetic parameters for kyphosis in two crossbred swine populations

Genetic parameters for degree of kypho- sis were estimated from a Duroc-Landrace F2 popula- tion (n = 316) and from a composite population (line C) composed of Duroc, Large White, and 2 sources of Landrace (n = 1,552). Live presentation did not indi- cate kyphosis in pigs or sows. Degree of kyphosis was measured by scoring the shape of the vertebral column of split carcasses on a scale from 0 (normal) to 3 (se- vere). Of the animals slaughtered, 75.6 and 68.9% were normal, 11.1 and 23.3% were mild, 11.1 and 6.2% were moderate, and 2.2 and 1.5% were severe in F2 and line C, respectively. Fixed effects of age, sex, number of ribs, number of lumbar vertebrae, number of nipples, carcass length, and HCW were not significantly asso- ciated (P > 0.10) with kyphosis score when using lin- ear models. Estimated heritabilities for kyphosis score were 0.30 and 0.32 in F2 and line C, respectively, when using an animal model. Estimated genetic correlations between kyphosis score and number of ribs, number of lumbar vertebrae, number of nipples, carcass length, and HCW were 0.05, −0.13, 0.00, 0.05, and 0.03, re- spectively. Selection to decrease kyphosis should be ef- fective and would not be expected to affect the number of ribs, lumbar vertebrae, nipples, or carcass length. In addition, selection for growth should not affect the incidence of kyphosis.