Evaluation of direct and correlated responses to family index selection for part period egg production in egg type chicken

IWH and IWI pure lines of White Leghorn were subjected to 6 generations (19 88-94) of family index selection (IDS) for part period egg production up to 280 days of age to evaluate direct and correlated responses at phenotypic and genetic level. A control line (IWC) was also maintained contemporarily along with the selected lines. The average realized genetic gains for part time egg production were estimated to be 1.18 and 2.18 eggs per generation in IWH and IWI lines respectively. The corresponding genetic gains in diffe rent correlated traits were - 0.17 and -0.60 g for 40th week egg weight; 0. 87 and -0.13 days for age at sexual maturity; 9.43 and 3.13 g for 20-week-b ody weight and 19.24 and 5.03 g for 40-week-body weight. Except for 20-week -body weight in IWH line, the responses in all the traits of both the selec ted lines were nonsignificant. The realized genetic gain did not agree well with expected one for all the traits in both the lines. Natural selection and inbreeding did not appear to be important factors in influencing the re sponses. The probable reasons for poor correspondence between realized and expected responses have been discussed.