QTL for osteoporosis detected in an F₂ population derived from White Leghorn chicken lines divergently selected for bone index

Osteoporosis, resulting from progressive loss of structural bone during the period of egg-laying in hens, is associated with an increased susceptibility to bone breakage. To study the genetic basis of bone strength, an F₂ cross was produced from lines of hens that had been divergently selected for bone index from a commercial pedigreed White Leghorn population. Quantitative trait loci (QTL) affecting the bone index and component traits of the index (tibiotarsal and humeral strength and keel radiographic density) were mapped using phenotypic data from 372 F₂ individuals in 32 F₁ families. Genotypes for 136 microsatellite markers in 27 linkage groups covering ~80% of the genome were analysed for association with phenotypes using within-family regression analyses. There was one significant QTL on chromosome 1 for bone index and the component traits of tibiotarsal and humeral breaking strength. Additive effects for tibiotarsal breaking strength represented 34% of the trait standard deviation and 7.6% of the phenotypic variance of the trait. These QTL for bone quality in poultry are directly relevant to commercial populations.