Abstract
Bone fractures at the end of lay are a significant problem in egg-laying strains of hens. The objective of the current study was to identify quantitative trait loci (QTL) associated with bone mineralization and strength in a chicken resource population. Layer (White Leghorn hens) and broiler (Cobb-Cobb roosters) lines were crossed to generate an F2 population of 508Â hens over seven hatches, and 26 traits related to bone integrity, including bone mineral density (BMD) and content (BMC), were measured. Genotypes of 120 microsatellite markers on 28 autosomal groups were determined, and interval mapping was conducted to identify QTL regions. Twenty-three tests representing three chromosomal regions (chromosomes 4, 10 and 27) contained significant QTL that surpassed the 5% genome-wise threshold, and 47 tests representing 15 chromosomes identified suggestive QTL that surpassed the 5% chromosome-wise threshold. Although no significant QTL influencing BMD and BMC were detected after adjusting for variation in body weight and egg production, multiple suggestive QTL were found. These results support previous experiments demonstrating an important genetic regulation of bone strength in chickens, but suggest the regulation may be due to the effects of multiple genes that each account for relatively small amounts of variation in bone strength.
Highlights
Osteoporosis is a progressive loss in structural bone and is a common problem in caged egg-laying strains of hens [60]
Our lab validated the use of dualenergy X-ray absorptiometry (DEXA) as a non-invasive tool for measurement of bone mineral density (BMD) and content (BMC) in live birds [41, 43]
These studies have focused on identifying quantitative trait loci (QTL) responsible for body weight [39, 46, 47, 51, 52, 55], feed-efficiency [57], growth [7,20,27,55,57,62], carcass characteristics [12, 23, 24, 56], and egg traits [27, 39, 44, 54, 59]
Summary
Osteoporosis is a progressive loss in structural bone and is a common problem in caged egg-laying strains of hens [60]. Bishop et al [4] reported a 2-fold improvement of bone strength in chickens after seven generations of divergent selection for a bone index. These selection experiments demonstrate that improvements in bone integrity can be made through genetic selection, they rely on measurement of traits that require euthanasia of the bird. DEXA is effective at measuring differences in bone strength among birds, it is a time consuming and labor intensive process These limitations of DEXA could be overcome if genetic markers for BMD and BMC are identified and incorporated into marker-assisted selection programs. Development of genetic markers for these traits will contribute to the improvement of bone integrity in chickens through marker assisted selection for increased bone strength
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