抄録
In this study a selection experiment was carried out in order to investigate the effectiveness of index selection including oviposition time as a selection trait for persistency of laying strain building in laying hens. The selection was applied by using an index consisting of age at first egg (SM), egg weight at 270 days of age (EW) and the rate of lay from 151 to 270 days of age between 06.00 and 11.00 h (6-11EP) under 14 hour light-10 hour dark cycle (photo period; 06.00 to 20.00 h).
After six generations of index selection, 6-11EP showed significant change, therefore short-term rate of lay from 151 to 270 days of age (SEP) and long-term rate of lay from 151 to 400 days of age (LEP) both improved significantly. Realized genetic gains per generation (P<0.01) were : 6-11 EP, 3.0%; SEP, 0.9%; LEP, 1.3%; rate of lay from 151 to 270 days of age between 11.00 and 20.00 h (11-20EP), −2.1%; residual-term rate of lay from 271 to 400 days of age (REP), 1.6%. Realized genetic gains were higher in 6-11EP than in SEP and LEP. However, improvement was not obtained in SM and there was not a marked genetic change in EW. The pooled heritability estimates for LEP and SEP were similar, 0.19 and 0.15 respectively, however the heritability estimate for 6-11EP was higher at 0.41. The genetic correlations pooled over 6 generations between LEP and egg production traits were all high and positive except 11-20EP: 6-11EP, 0.51; SEP, 0.71; REP, 0.94; 11-20EP, −0.25.
These results indicated that rate of lay including oviposition time are useful as selection traits. Therefore, the index selection consisted of 6-11EP was successful in persistency of laying strain building.
