PhD

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.