Forage intake and digesta kinetics of beef cattle differing in feed efficiency while grazing Idaho rangelands

Authors: SPRINKLE, JIM - University Of Idaho; WILLMORE, CARMEN - University Of Idaho; ELLISON, MELINDA - University Of Idaho; HALL, JOHN - University Of Idaho; LEWIS, RONALD - University Of Nebraska; TOLLESON, DOUGLAS - Texas A&M University; Jaramillo, David

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/2/2025
Publication Date: 1/12/2026
Citation: Sprinkle, J., Willmore, C., Ellison, M., Hall, J., Lewis, R., Tolleson, D., Jaramillo, D.M. 2026. Forage intake and digesta kinetics of beef cattle differing in feed efficiency while grazing Idaho rangelands. Journal of Animal Science. https://doi.org/10.1093/jas/skaf429.
DOI: https://doi.org/10.1093/jas/skaf429

Interpretive Summary: Efficiency is output divided by input. When discussing beef cattle efficiency, this is usually measured with feed intake within a controlled environment such as a feedlot. However, mature cattle that make up the US cow herd live primarily outside of confinement in open pasture and range systems. The main goal of this research was to characterize the forage intake of 24 two-year old lactating cows at both mid- and late-lactation while grazing rangeland pastures. This herd of cows had been previously classified as either efficient or inefficient based on residual feed intake. The results indicate there were no treatment differences between efficient and inefficient cows for the variables measured but period differences were present. Reliable estimates of intake with the pulse dose procedure were obtained but differences in intake in a feedlot setting did not translate to a range setting. Continued efforts should be made to evaluate the efficiency of cattle grazing rangeland along with methods to provide long term daily estimates of energetic demands for grazing livestock.

Technical Abstract: The objective was to determine if 2-yr old cows differing in residual feed intake (RFI) would differ in forage intake and digesta kinetics. Previously classified two-yr-old lactating Angus × Hereford cows {12 efficient, (EFF); 12 inefficient, (INE)} were given a pulse dose of an alkane marker. Fecal samples were then collected repeatedly over 4 days in June and August. Daily organic matter digestibility (OMD) and crude protein (CP) were estimated from fecal near infrared spectroscopy. Data were analyzed fitting a non-linear digesta kinetics model to individual cows. A mixed model with RFI treatment, period, and their interaction as fixed effects, and cow within treatment as a repeated random effect, was fitted to the combined kinetics data. There were no treatment differences (P > 0.05) between EFF and INE cows for the variables measured, but period differences were present (P < 0.05). Fecal output tended to increase from spring to summer (P = 0.09) and for INE cattle from spring to summer (P = 0.06) but EFF cattle did not differ from spring to summer (P = 0.60). Total marker residence time in the gastrointestinal tract (RTG) was 38.3 and 40.5 ± 1.2 h for INE and EFF cows, respectively in June, and 44.0 and 42.9 ± 1.2 h for INE and EFF cows in August, increasing (P < 0.001) for INE and tending to increase for EFF (P = 0.097). Period RTG was 39.3 vs 43.4 ± 0.8 h for June vs August (P < 0.01). Dry matter intake (DMI) in June for INE cows was 11.7 ± 0.87 kg and 13.2 ± 0.83 kg for EFF cows (P = 0.24). August DMI was 12.9 and 12.4 ± 0.83 kg for INE and EFF cows, respectively (P = 0.68). The OMD was 58.9 vs 53.8 ± 0.36 % for June vs August (P < 0.0001) and CP was 15.0 ± 0.23 vs 14.2 ± 0.22 % (P < 0.05). The CP in the diet declined from spring to summer for EFF cattle (P < 0.05), but not for INE cattle (P = 0.22). The compartmental mass of undigested dry matter (fill) was 5.7 vs 7.4 ± 0.36 kg for June vs August (P < 0.01). Bite rates increased from spring to summer (P < 0.05) and for EFF cattle (P < 0.05), but not INE cattle (P = 0.52). Grazing time tended to increase from spring to summer (P = 0.06,) and for INE cattle from spring to summer (P = 0.07), but not for EFF cattle (P = 0.41). Reliable estimates of DMI with the pulse dose procedure were obtained but differences in DMI for RFI in a feedlot setting did not translate to a range setting.