The genetics of leg weakness in Finnish Large White and Landrace populations

Data from six progeny-testing (1994-1997) and one performance-testing (1991-1998) stations were compiled and subsequently used in the estimation of genetic parameters for overall leg action and the five most severe symptoms of leg weakness: buck-kneed, small inner claws, legs turned out on the fore legs. small inner claws and upright pasterns on the hind legs. Overall leg action was assessed using a scale from 1 to 5. Leg traits were recorded differently in the testing methods (four classes in the progeny-testing and two classes in the performance-testing). Observations used for analysis were rescaled into frequency normalised scores. Final data contained records of 6115 Large White (LW) and 7043 Landrace (LR) pigs. Pedigree information included all animals born after the year 1986. Variance components were estimated by the restricted maximum likelihood method, using a statistical model that included additive genetic animal and litter as random effects and interactions between station*year*season as a fixed effect. Heritability estimates were low for overall leg action (0.06 for LR and 0.05 for LW) and low to moderate (0.01-0.17) for individual leg traits. The proportion of variance due to common litter environment ranged from 0.03 to 0.14, and in all cases was significantly greater than zero. There was a strong genetic correlation between buck-kneed on the fore legs and overall leg action (0.88+/-.07 in LR and 0.98+/-.09 in LW). whereas correlations between other traits were highly variable across breeds and had large standard errors. Overall leg action and buck-kneed on the fore legs were unfavourably correlated with fat and lean percentages, whereas standard errors of the other genetic correlations between leg and production traits were too high to allow conclusions to be drawn. (C) 2001 Elsevier Science B.V. All rights reserved.