Effects of dietary crude protein levels on growth performance, rumen characteristics, blood metabolites, and methane emissions in finishing Hanwoo steers.

Abstract

Objective: The objective of this study was to investigate the effects of increasing dietary crude protein (CP) concentration on growth performance, rumen characteristics, blood metabolites, and methane (CH4) emissions in finishing Hanwoo steers.

Methods: Twenty-four 26-month-old Hanwoo steers (717±50.1 kg) were utilized in a 12-week study based on a completely randomized block design. The animals were randomly assigned to one of four dietary treatments by feeding concentrate mixes with different CP levels (15.0, 16.2, 17.5, and 18.5% on a dry matter [DM] basis). Forage was fed ad libitum, while the concentrate mix was provided in a fixed amount.

Results: Forage and total dry matter intake (DMI) linearly increased (P ≤ 0.029) with increasing CP levels while concentrate intake was not affected by treatments. Initial and final body weight and average daily gain were not different among treatments. Feed efficiency showed a trend of linear decrease (P = 0.092) with increasing CP levels. Rumen parameters, including ruminal pH, total volatile fatty acid, molar proportions of acetate, propionate, isobutyrate, butyrate, isobutyrate, valerate, and acetate to propionate ratio, were not affected by treatments. Treatments also did not affect blood concentrations of total protein, urea, glucose, non-esterified fatty acid, albumin, creatinine, triglyceride, glutamic oxaloacetic transaminase, glutamic pyruvic transaminase, calcium, and phosphorus. Concentrations of CH4 from respiration or eructation were not affected by dietary CP. Methane ppm per DMI and neutral detergent fiber (NDF) intake was not also different among treatment in respiration or eructation. However, CH4 ppm per forage NDF intake linearly decreased (P ≤ 0.005) with increasing CP from both respiration and eructation.

Conclusion: These findings provide no clear evidence that increasing the CP content of the concentrate mix from 15.0 to 18.5% DM improves growth performance and body metabolism in finishing Hanwoo steers. Nevertheless, they suggest that a higher CP level may negatively affect feed efficiency.