Association Between Persistency of Lay and Partial Record Egg Production in White Leghorn Hens and Implications to Selection Programs for Annual Egg Production

The objectives of this experiment were: 1) to estimate the increase in accuracy of selection for annual egg production (YP123) based on partial record data (Yp12) by incorporating the predicted residual record (Yp3) into the selection objective, 2) to examine the effect of selection based on Yp12 versus Yp123 on the persistency of lay, and 3) to compare the relative efficiency of differential weighting of production periods on selection response. These objectives were accomplished by comparing expected responses per unit of time from alternative selection indices and examining genetic correlations among production traits, which were estimated from a pedigreed population of randombred White Leghorns. The traits were estimated from a 56-wk egg production curve, which was divided into 8-, 16-, and 32-wk periods corresponding to prepeak (Yp1), postpeak to end of partial record (Yp2), and residual (Yp3). Persistency was estimated by linear regression of production on months using either early postpeak (Bp2) or total postpeak (Bp23) records. Results indicated that: 1) Bp23 was negatively correlated with Yp1 and Yp2 but positively correlated with Yp3 and Yp123, thus, selection based on Yp12 is expected to have a deleterious effect on persistency, but selection based on Yp123 is expected to improve persistency; 2) Bp2 was poorly correlated with Yp3, thus, Ŷp3, the estimate of Yp3 from Yp2, did not improve the accuracy of selection; and 3) optimally weighting the portions of Yp123 gave expected annual responses equal to or greater than those obtainable from selection based on Yp12.