Effects of balanced selection for intramuscular fat and abdominal fat percentage and estimates of genetic parameters.

Intramuscular fat (IMF) content contributes to meat flavor and improves meat quality. Excessive abdominal fat, however, leads to a waste of feed resources. Here, an independent up-selection for IMF was used as a control (Line C), and a balanced selection program, with up-selection for IMF and down-selection AFP (Line B), was studied in JingXing yellow chickens. The mean of IMF and AFP within a family was the phenotypic value upon which selection was based. The selective pressures of IMF in line B and line C were the same in each generation. At G5, the IMF was significantly higher (P < 0.05) than that at G0 in both lines. For AFP, Line C was significantly higher at G5 (P < 0.05) than at G0, but the difference in Line B was not significant (P > 0.05). IMF increased by 11.4% and AFP decreased by 1.5% in Line B compared with the G0 generation. In contrast, the IMF increased by 17.6%, but was accompanied by an 18.7% increase in AFP, in control Line C. Of 10 other traits measured, body weight at 56 d age (BW56) and the percentages of eviscerated weight (EWP) showed a significant difference between the 2 lines (P < 0.05). The heritabilities for IMF and AFP, estimated by the DMU package, were 0.16 and 0.32, respectively. A moderate positive correlation existed between IMF and AFP (0.35). A balanced selection program for increasing IMF while controlling AFP (Line B) is shown here to be effective in practical chicken breeding.