Abstract
OBJECTIVE: This study investigated the effects of high-protein concentrates with two different rumen undegradable protein (RUP)-to-degradable protein ratios on the performance and carcass characteristics of Hanwoo steers reared for 26 months. METHODS: Thirty-two Hanwoo steers (217±13 kg) were randomly allocated to eight pens (four animals/pen) and assigned to one of two concentrate treatments (four pens/treatment), low-RUP concentrate (LRUP; RUP ratio of 37:63) or high-RUP concentrate (HRUP; RUP ratio of 47:53), with a dietary crude protein (CP) content of 20% dry matter (DM) during the growing stage (8 to 17 months) and 18% DM during the fattening stage (18 to 26 months). RESULTS: Increasing the RUP ratio in the concentrate reduced (p = 0.062) rumen ammonia (NH3-N) levels during the growing stage. A decrease (p<0.05) in the molar proportions of acetate and valerate, and an increase (p = 0.097) in the proportions of iso-valerate, was observed in the HRUP group. Significant improvements (p<0.05) in the average daily gain and the feed conversion ratio were observed in the HRUP group during the fattening stage. Although there were no significant group differences in carcass yield or characteristics in steers slaughtered at 26 months, a trend (p = 0.081) toward an increased rib-eye area was observed in the HRUP group. Relative mRNA expression profiling revealed higher lipid biosynthesis and lipolysis in the HRUP group at slaughter. However, no effects on intramuscular fat content was detected. CONCLUSION: Raising the RUP level improved performance and intramuscular fat metabolism in Hanwoo steers. The final body weight of the steers in the HRUP group was comparable to that of Hanwoo steers raised under the conventional 30-month fattening period. Overall, feeding a high-CP concentrate with a higher RUP proportion (47% CP) may be a beneficial strategy to shorten the feeding period.