Effect of starch and crude protein in supplemental feed on rumen fermentation, growth performance, and carcass characteristics in early- and late-fattening Hanwoo steers

Recently, there has been an increased focus on developing high-energy and high-protein feeds for Hanwoo steers in Korea to reduce the fattening period and decrease production costs. The aim of this study was to investigate the effects of different starch and crude protein contents in supplemental feed on rumen fermentation, growth performance, plasma metabolites, and carcass characteristics in early-and late-fattening Hanwoo steers. Sixty steers were randomly assigned to the following two groups based on the fattening stages: moderate-protein and high-starch (MPHS) and high-protein and moderate-starch (HPMS). The in vitro ruminal pH and ammonia concentrations in steers fed the MPHS supplemental feed were lower than those on HPMS supplemental feeds. The propionate concentration was higher in the MPHS supplemental feed in both the early-and late-fattening stages. During late fattening, average daily gain was 0.93 and 0.82 in the MPHS and HPMS groups, respectively, with a higher value in the MPHS group. In early-fattening Hanwoo steers, plasma creatinine, calcium, phosphorus, and magnesium concentrations in the MPHS group were higher than in the HPMS group. The rib-eye area in the MPHS group was 98.60 and 93.60 in the HPMS group. The marbling score in the MPHS group tended to be higher than in the HPMS group. Increasing the starch energy content rather than the crude protein content in the supplemental feed exerts a positive effect on rumen fermentation, growth performance, carcass weight, and rib-eye area in Hanwoo steers during the early and late fattening periods.