Effects of Intake Levels of High-Protein and High-Rumen Undegradable Protein Concentrate on Carcass Characteristics of 26-Month-Slaughtered Hanwoo Steers.

Abstract

Shortened 26-month feeding program in Hanwoo steers often impair intramuscular fat (IMF) accumulation and carcass marbling. Therefore, this study examined whether increasing the intake level of a high-crude protein (CP) and high-rumen undegradable protein (RUP) concentrate could overcome these marbling limitations. Thirty-two Hanwoo steers (initial body weight (BW) 217 ± 14 kg; 8 months of age) were randomly assigned to low (LI; n = 16) or high (HI; n = 16) nutrient intake groups. Both groups were fed a high-CP and high-RUP concentrate diet at differing intake levels. During the growing stage (8 to 17 months), concentrate dry matter intake was ~10% higher in the HI group (5.23 vs. 4.59 kg/d; p < 0.001), increasing intakes of CP (1.23 vs. 1.11 kg/d; p < 0.001), RUP (0.57 vs. 0.52 kg/d; p < 0.001), and total digestible nutrients (5.40 vs. 5.17 kg/d; p = 0.093). Intakes did not differ during the fattening stage (18 to 26 months). Final body weight (746.9 vs. 744.0 kg) and average daily gain were unaffected by treatment. However, steers in HI group exhibited improved carcass quality, including a trend toward larger rib-eye area (89.5 vs. 83.9 cm²; p = 0.088) and significantly greater marbling area (20.4 vs. 16.3 cm²; p = 0.031) and IMF content (19% vs. 15%; p = 0.028). Enhanced intake during growing stage increased total volatile fatty acid concentration (114.5 vs. 95.2 mM; p = 0.002). At 17 months, muscle biopsy revealed downregulation of peroxisome proliferator-activated receptor alpha (p < 0.05) alongside upregulation of lipoprotein lipase (p < 0.01) and diacylglycerol acyltransferase-2 (p < 0.10) in HI group, indicating activated lipogenesis. These findings suggest that nutritional enhancement during the growing stage, even without sustained elevation during the fattening stage, can successfully overcome the IMF limitations of a shortened 26-month program, driving adipogenic growth.