Genetic parameters for osteochondrosis in Danish Landrace and Yorkshire boars and correlations with leg weakness and production traits

The purpose of this study was to estimate the heritabilities and the geneti c correlations of osteochondrosis in different joints and to estimate genet ic correlations between osteochondrosis, leg weakness and production traits . The humerus condyles, anconeal process, distal ulna growth line, femoral condyles, distal tibia and medial trochlear ridge of talus on both sides of the animals were examined radiologically for osteochondral lesions and sco red from 1 to 5 with increasing severity. The boars were also scored for 13 different leg weakness traits on a scale from 1 (normal) to 5 (very severe changes). During a 3-year period, a total of 2042 Landrace boars from 256 sires and 1946 Yorkshire boars from 240 sires were examined at a mean weigh t of 93 kg. The data were analysed by animal models for each breed. The Lan drace was found to be more severely affected than the Yorkshire regarding o steochondrosis in all localities expect the anconeal process. The genetic c orrelations between left and right side scores of the osteochondral trait w ere close to 1. This indicates that genetically the same trait is measured in the left and in the right side of the animal. The heritability of averag e osteochondrosis scores teas low to moderate ranging from 0.08 to 0.39 (s. e. between 0.02 and 0.04). The genetic correlations between osteochondrosis in the different body localities were low indicating that osteochondrosis is Mot a generalized disease. The Landrace was more severely affected than the Yorkshire regarding all leg weakness symptoms except buck-kneed foreleg s, forelegs turned out and weak pasterns on forelegs. The heritability of l eg weakness traits ranged from 0.02 to 0.35 (s.e, between 0.01 and 0.04). G enetic correlations between osteochondrosis and leg weakness showed a clear picture for the Yorkshire breed regarding the humeral condyles: positive c orrelations with buck-kneed forelegs, forelegs turned out, stiff in front a nd rear. In both breeds osteochondrosis in femoral condyles showed a high p ositive correlation with hind legs turned out and a lower positive correlat ion with stiff in front. The sum of osteochondrosis traits (sumost) was unf avourably genetically correlated with daily gain, whereas the sum of leg we akness traits (sumleg) teas unfavourably correlated with lean meat percenta ge in both breeds. The correlation between the summary measures sumost and sumleg was 0.09 (s.e. 0.11) in the Landrace and -0.07 (s.e. 0.12) in the Yo rkshire.