Abstract
Three strains (L3, L5 and L8) of White Leghorns reproduced by random mating in a closed population for over 20 yr were subjected to family selection for annual egg production. The annual egg production period was divided into various part period segments with their corresponding residual egg production records. Combined estimates of heritabilities and genetic correlations were calculated for each segment of the production curve. Relative efficiency of the genetic progress expected in the annual and residual records using part record vis-à-vis complete part record was estimated. For each part period segment heritabilities were the same – whether they were estimated from egg number or from percent production – and showed very high values when estimated from a segment that includes the 21st wk. Heritabilities of the residual records were low for the L3 and moderate for the L5 and L8 strains. Percent production or egg number of the complete part record showed a very high genetic correlation with annual egg production in all strains, a high genetic correlation with residual record in the L8 strain, and a low genetic correlation with residual record in the L3 and L5 strains. A very high annual relative selection efficiency could be obtained by using for selection the percent production of complete part record, but the persistency of layers could be increased by using for selection the percent production of other partial records.
Published Version
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