Study for detecting quantitative trait loci affecting eggshell strength

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Improvement of commercial layers is approaching breeding goals in the viewpoint of productivity. Next targets for breeding are reducing economic loss. Broken and cracked eggshells cause major economic loss for egg production. Roland (1988) estimated that the rate of inadequate shells was 7.7% at all production stages, and then 5.16% of broken eggs in the commercial activities, both caused totally 13-20% of egg loss. Therefore, breeding for egg shell strength is needed. The aim of this study is to identify quantitative trait loth (QTL) affecting egg shell strength in White Leghorn.An F2 population of 262 hens, obtained by crossing a strong egg shell line with a weak egg shell line of White Leghorn, was used for detecting quantitative trait loci affecting egg character. The two lines were developed from the same line, D2(Okazaki Station, National Livestock Breeding Center of Japan), by two-way selection for egg shell strength with nondestructive deformation Nirasawa et al., 1998). 1,014 microsatellite markers including 696 ABR markers were used, which are covered whole chicken genome. QTL analysis was performed using QTL Express (Seaton et al,1994)Of the markers u sed, 35 markers were informative and mapped on 10 autosomal linkage groups. There was no informative marker on chromosome Z. The QTL for 7 traits, i. e., body weight (BW), egg weight (EVE, short length of egg (SL), long length of egg (LT..), shell strength (SS), shell thickness (ST) and shell weight (SW)) were identified. Highly significant (p<0.01) QTL for ST, SW and LL were identified a region flanking with ABR0362 and ABR0545 on chromosome 9. These QTL are good candidates for the reduction of broken and cracked eggs in wmmercial layers by marker assisted selection (MAS).