Selection studies in chicken for egg number on part records

Abstract

All India co-ordinated Research Project on Poultry Breeding for egg located at Kerala Agricultural University, Mannuthy , Trichur is maintaining two strains of white Leghorn which are subjected to selection for high egg production since 1978. The criterion of selection has been IDS method of index selection by combining the information on sire and dam family averages with the individual’s performances, for egg number up to 280 days of age. The present investigation was planned with the following objectives. -To evaluate the response of intrapopulation selection for part period egg production. -To estimate the genotypic and phenotypic parameters for different traits. -To evaluate the the correlated responses in unselected traits. -To measure the time trend in genetic parameters. -To measure the interstrain variation for some economic traits. To achieve these objectives data collected over a period of five generations, including base generation, on the experimental populations were utilized. Chicks hatched during 1979-80 hatching year of each strain constituted the foundation stock (S0). Thereafter both strains were subjected to four generations of selection. Standard managemental throughout experimental period. practices were followed uniformly The traits measured were egg number up to 280 day of age (EP), age at first egg in days (ASM), body weight in grammes at 20 and 40 weeks of age (20 wk-40 wk BW ) and egg weight (BW) in grammes at 30.40 weeks of age. The average effective number of male breeders, female breeders and progenies with complete records were 40, 238.4 and 1165.8 in IWN and 39.8, 232.2 and 1076.6 in IWP strains, respectively, over generations. The effective populations size over generations were 136.62 in IWN and 135.33 in IWP strains. The coefficient of inbreeding increased by two per cent in both populations over four generations of selections which would be the upper limit due to intentional avoidance of sib matings. Since hatch effects were significant for most of the traits, data were corrected for hatch effects before analysis by fitting least square constants. The heritability of each trait and correlations between traits were estimated initially intra generation-strain basis following variance and covariance component anaylsis and then pooled over generations within strain to provide mean estimates. The heritability estimates of various traits obtained in this study were consistent with several earlier reports. Sexlinked effects appeared to be important in the inheritance of EP 20 WK, BN, EW and ASM in IWP strain whereas maternal effects wee important for 40 WK, BN. But sex-linked effects for 40 weeks BN appeared to be important in IWN. The genetic and phenotypic correlations of the present study were close to several earlier reports both in direction and magnitude. The genetic parameter estimates did not show any significant time trends due to four generations of selection in both populations. The realized phenotypic response per generation obtained from regression of generation means on generation number were 8.30 + 1.60 eggs in IWN 5.37 + 1.6-0 eggs in IWP strains, which were significantly different from zero. The correlated response per generation for ASM, 20wk BN, 40 wk BN and BN due to selection for part period egg number were-4.26 d, 28.46 g, - 10.32 g, -0.28 in IWN and –4.45 d, 37.28 g, -13.80 g, -0.02 g in IWP strains, respectively. The realized gains in selected and unselected traits agreed well with the predicated response in direction but not in magnitude, except 40 wk in IWP which was in opposite direction. For all the traits the realized gains were found to be higher than the predicted gains except BN of IWP which was less than the predicated response. Difference were highly significant between the two strains for all the traits under study in the generation except S2 for BN : S0 for ASM, 20 wk BN: S3 for 40 wk BN : S0, S1 and S3 for BN.