Correlated Responses to Selection for High or Low Incidence of Tibial Dyschondroplasia in Broilers

Abstract

Selection for a high or a low incidence of tibial dyschondroplasia (TD) at 7 wk of age was practiced for four generations in broiler breeders keeping an unselected control (C) line and using low intensity X-ray imaging for TD diagnosis. The incidence of TD, BW at 4 and 7 wk of age, age at first egg, and egg production for the first 12 wk of production were determined in the four generations. Age at initial semen production and semen volume and concentration of males were determined only in Generations 3 and 4. The TD scores and BW at 7 wk were collected on 1,366, 1,301, and 1,389 broilers from the C, high (H), and low (L) incidence of TD lines. Incidence of TD at 7 wk in the fourth generation was 16.1, 61.9, and 3.5% for the C, H, and L lines, respectively. There were no significant differences in BW between the H and L lines in Generations 1, 3, or 4. However, in Generation 2, the H line was heavier (P < .01) than the L line. Second generation H line broilers with TD were heavier than those without TD at 4 and 7 wk of age (P < .01). There were no significant differences in age at first egg, age at semen production, or in semen volume between the H and the L lines. Egg production in the L line was greater (P < .01) than that of the H line in all four generations, and semen concentration was also greater (P < .01) in Generations 3 and 4. Correlated responses to selection in the H and the L line were estimated per generation and per weighted selection differential (WCSD) for the traits that were recorded in the four generations. Regression coefficients of cumulative response per generation and per unit of WCSD were not significant.