Evaluation of average performance of some economic traits under long term selection programme over various generations in a closed flock of White Leghorn

Change in mean performance of a White Leghorn population under the influence of constant selection over 12 generation was evaluated. The traits studied were body weight at 20 weeks, age at first egg, egg number upto 280 days and egg weight at 40 weeks of age. In selected line, 20 week body weight and egg weight showed little changes over different periods. The age at first egg showed significant decline up to Period-III (167 to 152 d) while showed increase in Period-IV (157.88 d). The egg nwnber improved considerably upto Period-II (69.8 to 89.4) and declined subsequently to 79.24 in Period-IV. The subsequent decline in egg number after Period-II and maintenance of egg weight at same level may be due to shifting of selection priorities on egg weight in later periods. The average effective population size ranged from 84.05 to 112.53, while the expected rate of inbreeding per generation ranged from 0.45 to 0.59 resulting in a cumulative inbreeding of 6.23% over a period of 12 generations. The drift variance and error variance per generation were low. In control line except 20 week body weight other traits showed wide fluctuations, particularly in later periods which may be attributed to environmental factors.