Study for detecting quantitative trait loci affecting eggshell strength

从生产力的角度来看，商品蛋鸡的改良正在接近育种目标。育种的下一个目标是减少经济损失。蛋壳破碎、破裂给蛋品生产造成重大经济损失。罗兰（Roland，1988）估计，在所有生产阶段，壳的不合格率为7.7%，而在商业活动中的破蛋率为5.16%，两者共造成13-20%的蛋损失。因此，需要对蛋壳强度进行育种。以262只白来航蛋鸡的强壳系与弱壳系杂交F2群体为材料，对影响蛋品质的数量性状基因座进行了检测。这两个品系是从同一品系D2（冈崎站，日本国家家畜育种中心）通过对蛋壳强度进行双向选择与非破坏性变形Nirasawa等人，1998年）。共使用了1,014个微卫星标记，其中ABR标记696个，覆盖了鸡的全基因组。使用QTL Express（Seaton等，1994）进行QTL分析。在所使用的标记中，35个标记是信息性的，并定位在10个常染色体连锁群上。在Z染色体上无信息标记。7个性状的QTL，即：例如，体重（BW）、蛋重（EVE）、短蛋长（SL）、长蛋长（LT）、壳强度（SS）、壳厚度（ST）和壳重量（SW））。在9号染色体上的ABR 0362和ABR 0545侧翼区域鉴定了ST、SW和LL的高度显著（p<0.01）QTL。这些QTL是利用标记辅助选择（MAS）减少商品蛋鸡破蛋率的良好候选基因。

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).