Data were collected from seven generations of selection for reduced time interval between oviposition in a line of Single Comb White Leghorns. This study involved 151 sires, 539 dams, and 2100 female progeny. Oviposition time was measured from 174 to 280 days of age. The only deliberate selection practiced was for reduced oviposition time interval. The mating system was random with the restriction of full or half sib matings. The reduction in oviposition time interval has been 73 minutes or 4.8 percent. There were no significant changes for total egg number, body weight or age at first egg. Rate of lay after reaching 50 percent production to 280 days has increased (P less than .07). Egg weight has declined five percent. Heritability estimates for intra-clutch time interval from correlations were .33 +/- .08, .36 +/- .09 and .35 +/- .15 by sire, dam, and combined components, respectively, .36 +/- .15 by regression of offspring on dam and .39 for realized. The magnitude of the selection differential decreased, over time. The genetic correlation of time interval with early production (280 days) was --.43 +/- .13, and with total egg production (500 days) was .20 +/- .27. The genetic correlations of time interval with egg weight and age at first egg were high and positive; and with body weight, it was negative. The increase in clutch size and the days between clutches during the time of this study were both highly significant.
The effectiveness of two way selection for serum alkaline phosphatase (S.A.P.) was investigated to determine its influence on productive traits in a White Leghorn population for three generations. The difference between females in the high and low lines at the end of three generations was S3 percent of the S.A.P. level of the foundation population. Selection was based entirely on phenotypic differences. The divergence of the lines was significant and greater in the high line. Computed heritabilities from within sire dam offspring regression for S.A.P. was .42. Heritability estimates from the analysis of variance sire component was .12 ± .09, and from the dam component .76 ± .16. The realized heritability was .45 and .36 for high and low lines respectively.No correlated responses were found during the time of this study for hen day egg production, egg weight, specific gravity or mortality. Hatchability decreased significantly in the high line and fertility decreased significantly in the low line.A build up of phosphatase in the blood occurred during the formation of the egg which would be an indication that the enzyme is involved in egg shell formation.
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