Analysis of Longissimus thoracis Protein Expression Associated with Variation in Carcass Quality Grade and Marbling of Beef Cattle Raised in the Pacific Northwestern United States.

Longissimus thoracis (LD) samples from 500 cattle were screened for protein expression differences relative to carcass quality grade. The LD of the top 5% (low prime and high choice, HQ) and bottom 5% (low select, LQ) carcasses were analyzed using two-dimensional difference gel electrophoresis and Western blot. Following initial screening, 11 candidate proteins were selected for Western blot analyses. Differentially expressed proteins were clustered into four groups: (1) heat shock proteins and oxidative protection, (2) sarcomeric proteins (muscle maturity and fiber type), (3) metabolism and energetics, and (4) miscellaneous proteins. Proteins from groups 1 and 2 were greater in HQ carcasses. Alternatively, increased quantities of proteins from group 3 were observed in LQ carcasses. Proteomic differences provide insights into pathways contributing to carcass quality grade. A deeper understanding of the physiological pathways involved in carcass quality grade development may allow producers to employ production practices that improve quality grade.