Divergent genetic selection for incidence of tibial dyschondroplasia in broilers at seven weeks of age.

Selection for a high (H) or low (L) incidence of tibial dyschondroplasia (TD) at 7 wk of age was practiced for four generations in broiler breeders using low intensity x-ray imaging (Lixiscope) for TD diagnosis. As a result, broiler lines with H or L incidence of TD at 7 wk of age were developed keeping a randomly selected control (C) broiler line. A total of 4,232 chicks were hatched representing 172 sires and 612 dams over four generations for the H, L, and C lines. The TD scores at 7 wk were collected on 4,056 broilers. Incidence of TD at 4 and 7 wk of age were studied in the C, H, and L lines of broilers. Direct response to selection in the H and L lines were estimated per generation and per weighted cumulative selection differential (WCSD). Total WCSD deviation from the C line for incidence of TD at 7 wk of age was 1.496 and -.42 units for the H and the L lines, respectively. The response per generation for incidence of TD at 7 wk of age for the H line was .153 +/- .028 units. The realized heritability for the H line for incidence of TD at 7 wk of age was .437 +/- .065. The incidence of TD was not significantly decreased in the L line at 7 wk of age.