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 and outfitted with grazing collars. Fecal samples were then collected repeatedly over 4 days in June and August. Daily digestible organic matter (DOM) and crude protein (CP) were estimated from fecal near infrared spectroscopy. Data were analyzed by 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 = 0.08) and for INE cattle from spring to summer (P = 0.06) but EFF cattle did not differ from spring to summer (P = 0.59). 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 39.4 vs 43.4 ± 0.8 h for June vs August (P < 0.01). Dry matter intake (DMI) in June was 15.6 ± 1.15 kg for INE cows and 17.6 ± 1.10 kg for EFF cows (P = 0.22). August DMI was 17.0 and 16.3 ± 1.10 kg for INE and EFF cows, respectively (P = 0.67). The DOM 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 6.6 vs 8.6 ± 0.42 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). Reasonable, though slightly inflated 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.
- Forage intake and digesta kinetics of lactating beef cattle differing in feed efficiency while grazing Idaho rangelands
- James E Sprinkle - University of Idaho, Animal, Veterinary, and Food SciencesCarmen M Willmore - University of IdahoMelinda J Ellison - University of Idaho, Animal, Veterinary, and Food SciencesJohn B Hall - University of Idaho, Animal, Veterinary, and Food SciencesRonald M Lewis - University of Nebraska–LincolnDouglas R Tolleson - Texas A&M UniversityDavid M Jaramillo - Agricultural Research Service
- Journal of animal science, skaf429
- Oxford University Press
- 996866744501851
- © The Author(s) 2025. Published by Oxford University Press on behalf of the American Society of Animal Science. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/pages/standard-publication-reuse-rights)
- Rangeland Center; Nancy M. Cummings Research, Extension, and Education Center; Animal, Veterinary, and Food Sciences
- English
- Journal article