RECIPROCAL RECURRENT SELECTION FOR FEED-EFFICIENCY IN LAYING HENS

Improvement of food conversion rate (FCR) by reciprocal recurrent selection in laying hens has been achieved. Records of individual food consumption (FC), number of eggs (EN), egg weight (EW) and body weight (W) were collected during three periods of four weeks each at the beginning of the laying periods. In the eight generations altogether 13408 hens were available in two selection lines, their reciprocal crosses and in corresponding controls. Significant strain differences developed for the selection criterion as well as in correlated traits. The selected hens were superior to the controls in FCR, laying rate (LR), EW and egg mass (EM). Realised selection indexes in retrospect for FCR of sires resp. dams were identified. They were used to estimate the cumulative selection differentials and expected selection responses for FCR. The cumulative selection differentials of this index for FCR of sires 33 and 44, resp. and dams 33 and 44 resp. were increased from 0.14 to 1.56, from 0.58 to 4.19, from 0.19 to 1.94 and from 0.62 to 4.70, respectively, nearly linearly for seven generations. The realised selection responses of FCR varied (desirably) in reciprocal crosses 34 and 43 resp. from -0.09 to -0.31, from -0.01 to -0.18 and in pure (parental) lines 33 and 44 resp., from 0 to -0.23 and from 0.09 to -0.19, respectively, from generation 1 to 7. The realised heritability of the index of line 33 for FCR in the reciprocal crosses was 0.15 resp. 0.19, that of line 44 was 0.04 resp. 0.05. The expected selection responses of FCR in cross 43 were greater than the realised responses, while those of cross 34 were vice versa greater than expected. The realised responses were not significantly different from expected ones. W was decreased, EW and LR was increased. A slight decrease or no change in FC was found.