SELECTION FOR IMPROVING EGG PRODUCTION IN MANDARAH CHICKENS TO MAXIMIZE THE NET INCOME. 1- CORRELATED RESPONSES, GENETIC PARAMETERS FOR EGG PRODUCTION AND GROWTH TRAITS

The aim of the present study was conducted to estimate the correlated response, the genetic parameters (heritability, genetic and phenotypic correlations) of some egg number and growth traits in Mandarah chickens for improving egg number at the first 90 days of laying along three successive generations. Results showed significant differences between selected and control lines as well as among generations. The realized and expected response over two generations were increased body weight at hatch (BW0) 1.23 gm and body weight at four weeks (BW4) 20.27 gm, but decreased body weight at 12 weeks of age (BW12) -15.87, -75.62 gm for male and female. Growth rate was increased at different periods except female (Gr 4-8) decreased. Also, noticed that selection for increasing egg number during first 90 days of laying in Mandarah strain increased egg mass (232.7 g) and feed conversion (0.17 g)  and reduced age at sexual maturity (- 8.06 days) and average egg weight (-0.47).
Estimates of heritability were (0.62 and 0.49) for ASM, and for BWSM (0.41 and 0.21), EN (0.35 and 0.38), EW (0.59 and 0.32), EM (0.39 and 0.36), feed conversion (0.37 and 0.22) for both the selected and control lines, BW0 (0.13 and 0.16), BW4 (0.32 and 0.31), BW8 (0.58 and 0.53) and BW12 (0.61 and 0.59) for both the selected and control lines, respectively. Genetic correlation in egg number in the selected line were positively associated with BW4 (0.21), BWSM (0.27) and EM (0.79), while, it with BW8 and BW12 weeks of age (-0.35 and -0.24), ASM (-0.39) and EW (-0.41) were negatively associated with egg number. There were low relationships between EN and the other traits studied. Genetic correlations between the other egg number and body weight traits showed a different genetic pattern in both selected and control lines. It could be concluded that selection for increased egg number during the first 90 days of laying in Mandarah strain decreased body weight and growth rate at different age. Heritability estimates based on sire component were higher for the selected line than the control one, which indicated that selection affected the heritability estimates.