Animals, experimental period, and feed management

Nineteen Hanwoo cows (mean age = 32.3 ± 6.9 months, mean body weight = 436.7 ± 38.3 kg) were from the Hanwoo Research Institute, National Institute of Animal Science, Rural Development Administration, Korea, were used in the study. Animal study design were approved by the Institutional Animal Care and Use Committee of the National Institute of Animal Science, Korea (Approval number: NIAS 20191557). The cows were randomly divided into three groups: 80%, 100%, and 120% NR groups (containing 6, 8, and 5 cows, respectively). The mean body weight was described as shown follow: 80% NR group = 455.0 ± 28.3 kg, 100% NR group = 417.8 ± 26.9 kg, 120% NR group = 437.4 ± 52.3 kg. All the cows were raised in a pen using a group feeding procedure based on the Korean feeding standard for Hanwoo cows. Commercial formulated concentrates and hay (straw rice) were fed to Hanwoo cows according to the experimental design from December 26, 2018 to April 29, 2019. The 100% NR group (control) was fed 2.0 kg of formulated concentrate and 4.0 kg of hay per cow. The 80% NR group was fed 1.5 kg of formulated concentrate and 2.4 kg of hay per cow. The 120% NR group was fed 3.0 kg of formulated concentrate and 5.0 kg of hay per cow. The chemical compositions of the concentrates and hay are provided in Table 1.

TDN, total digestible nutrients.