Relationships of a transforming growth factor-β2 single nucleotide polymorphism and messenger ribonucleic acid abundance with bone and production traits in chickens

Osteoporosis is a serious problem for the laying hen industry with economic, production, and welfare consequences. Transforming growth factor-beta 2 (TGF beta 2) has been implicated as an important factor in coupling bone resorption and formation in bone remodeling. The current study was designed to determine if TGF beta 2 was associated with variation in bone mineralization in chickens, using 2 complementary experimental approaches. First, an intronic single nucleotide polymorphism (SNP) present in TGF beta 2 was investigated in an F-2 population to determine its association with bone, growth, and egg traits of importance to the layer and broiler industries. The TGF beta 2 SNP was significantly associated (P < 0.05) with bone mineral density and content. However, these associations became nonsignificant when BW was included as a covariate in analyses. The TGF beta 2 SNP was also significantly associated (P < 0.05) with BW from I to 6 wk of age and egg production from 46 to 55 wk of age. To further explore the relationship between TGF beta 2 and bone strength, bone marrow TGF beta 2 mRNA abundance was compared between broiler and layer chickens at 15, 35, and 60 wk of age. Bone and egg traits were measured along with mRNA abundance at each age and found to differ significantly between lines. The TGF beta 2 mRNA abundance was approximately 4-fold greater in broiler compared with layer hens at 15 wk of age but was similar between lines at later ages. Thus, even though the TGF beta 2 SNP will likely not be an effective marker for improving bone strength independently of changes in BW, further research is warranted to investigate the relationship of TGF beta 2 mRNA abundance to bone strength in laying hens.