GENETIC ANALYSIS OF VARIOUS PRODUCTIVE AND IMMUNOCOMPETENCE TRAITS IN WHITE LEGHORNS UNDER LONG TERM SELECTION
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Date
2008-11
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SRI VENKATESWARA VETERINARY UNIVERSITY TIRUPATI - 517 502. (A.P.) INDIA
Abstract
ABSTRACT:
A study was conducted on three strains of White Leghorns viz., IWH, IWI and IWK and a control population. Significant strain differences were observed for all the traits studied viz., age at first egg, body weights at 4, 6, 10, 16, 20, 40, 52 and 64 weeks of age, egg production up to 40, 64 and 72 weeks of age. Egg production up to 64 and 72 weeks of age was highest in IWI (207.388+1.244 and 235.23+4.08 respectively). Egg production up to 40, 64 and 72 weeks of age was lowest in the control population. Egg weight was found to be highest (49.07+0.15, 54.23+0.17, 55.56+0.18 and 58.36+0.18 g respectively) in IWK strain at 28, 40, 52 and 64 weeks of age. The heritability value estimated from sire+dam component of variance indicated that the age at first egg and egg production were low to moderately heritable while body weights and egg weights at various ages were moderate to highly heritable. The genetic and phenotypic correlation of age at first egg with early body weights up to 20 weeks was mostly negative. The genetic and phenotypic correlations between part periods and annual egg production were mostly positive and high. Egg production up to 40 weeks and egg weight at 28 and 40 weeks has a consistently negative genetic and phenotypic association in all the populations studied. The genetic and phenotypic correlation of egg weight at 28 weeks of age with egg weight at 40, 52 and 64 weeks of age was mostly positive with varying magnitudes. Diallel analysis of the purebred and strain cross data revealed that the GCA, SCA and reciprocal effects were all significant for age at first egg and body weight at 20 weeks while only the GCA and SCA effects were significant for body weight at 40 weeks. The variances due to GCA and reciprocal effects were significant for egg production up to 40 weeks while, for egg production up to 64 weeks of age SCA and reciprocal variances were significant. The combining ability analysis on egg weight revealed that the variances due to both GCA and SCA were significant for egg weight at all the ages studied. Estimation of heterosis revealed significantly favorable heterosis for body weight at 20 weeks, egg production up to 64 weeks and egg weight at 64 weeks in most of the crosses.
Significant differences in antibody titer against SRBC and NDV were observed among the three strains and control population. The heritabilities of antibody titers against SRBC, NDV and cell mediated immunity to PHA-P injection varied from 0.227+0.084 to 0.716+0.115, 0.003+ 0.676 to 0.982+ 0.394 and 0.084+0.513 to 0.672+0.588 respectively. The phenotypic correlation of antibody titers against SRBC with egg production up to 64 and 72 weeks of age was negative in three of the four populations studied. The phenotypic correlation with antibody titer against NDV was mostly positive. The phenotypic correlation of antibody titer against NDV and cell mediated response to PHA-P with age at first egg was positive in all the strains. The correlation of antibody titer against NDV and cell mediated response to PHA-P with egg production was mostly positive.
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