High Roughage Diet Alters Performance, Carcass Characteristics, and Adipogenic Gene Expression of Bovine M. Longissmus Thoracis

Three groups of calf-fed steers were used to evaluate the effects of control (100% concentrate), IRG (Italian Rye Grass) silage (Ad libitum with 66% concentrate), and IRG hay (Ad libitum with 66% concentrate) on adipogenic gene expression in longissimus thoracis (LT) muscle. Eight randomly selected Hanwoo steer from each group were fed with a three step diet, which were calf diet (6~11month), early fattening diet (12~20month), and final fattening diet (21~30month). One gram of muscle biopsy samples was taken from cattle on 7, 12, 24 and 30 month on both sides of LT area. Real-time PCR determined the levels of adipogenic markers (C/EBPβ, PPARγ, SCD, GPR43) and myogenic markers (Pax3, Myf5, myogenin, GLUT4, MHCI, MHCIIA, MHC IIX) mRNA. Data were analyzed as a completely randomized design using the MIXED model, each treatment performed in triplicated. Means were considered different at P<0.05. Average daily gain at calf and early fattening period of study were not different but final fattening period of the study was lower in IRG hay group (P<0.05) than in control steers. Back fat thickness, ribeye area, and carcass weight of the control group were greater than those of IRG diet group (P<0.05). However, marbling score and shear force (kg/0.5in²) were not different among control and IRG diet. Relative PPARγ and SCD mRNA levels in biopsy samples were increased (P<0.05) on the days of fattening diet, but relative C/EBPβ mRNA level was decreased (P<0.05). The level of Pax3, Myf5, and myogenin were decreased on the days of fattening diet (P<0.05). Relative MHC 2X mRNA levels was greater (P<0.05) in 12month of age Hanwoo steer than in control steers. IRG hay group cattle had greater MHCIIX mRNA levels than other groups (P<0.05). These data indicate that relative mRNA levels of adipogenic genes in LT muscle are decreased during the days of high roughage diet (IRG silage and hay). High roughage diet also decreased back fat thickness and ribeye area but not affect marbling score.