Grazing behavior and production characteristics among cows differing in residual feed intake while grazing late season Idaho rangeland

Authors: SPRINKLE, JAMES - University Of Idaho; Taylor, Joshua - Bret; Clark, Pat; HALL, JOHN - University Of Idaho; Strong, Nicole; ROBERTS-LEW, MEGHAN - University Of Idaho

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/3/2019
Publication Date: 12/10/2019
Citation: Sprinkle, J.E., Taylor, J.B., Clark, P., Hall, J.B., Strong, N.K., Roberts-Lew, M. 2019. Grazing behavior and production characteristics among cows differing in residual feed intake while grazing late season Idaho rangeland. Journal of Animal Science. 98(1):1-9. https://doi.org/10.1093/jas/skz371.
DOI: https://doi.org/10.1093/jas/skz371

Interpretive Summary: Residual feed intake (RFI) is expressed as the difference between expected feed intake and actual feed intake. Simply put, it is an indicator of how efficient a cow might be with converting feed to body mass. A cow with a low RFI value is assumed to be more efficient that a cow with a high RFI value. We set out to determine if young two-year-old cows classified as having a low RFI value differed from cows having a high RFI value with regard to changes body weight, condition score, and grazing behavior while grazing extensive sagebrush rangelands in early winter. We found that low-RFI cows were leaner (less fat as indicated by a lower condition score) than high-RFI cows at the beginning of the grazing study. As time went on, however, the low-RFI cows lost less weight and by the end of the study had an equal condition score (estimate of fat) as the high-RFI cows. Overall, the grazing behavior, determined as distance traveled each day, was similar between the groups. Based on this evidence, we concluded there is opportunity for selection of more efficient cows that eat less while grazing extensive rangelands.

Technical Abstract: The objectives were to determine if cows classified as either low- or high-residual feed intake (LRFI or HRFI) differed in BW, BCS, and winter grazing activity over time. Thirty Hereford × Angus (LRFI = 16; HRFI = 14) 2-yr-old cows grazed sagebrush steppe for 78 d beginning 29 September 2016. Body weight and BCS were collected before and after grazing. Five cows of each RFI classification were fitted with global-positioning-system (GPS) collars on 16 November 2015 with data collection commencing 3 d later and continuing for 25 d in a 323-ha pasture. The GPS units collected location coordinates every 2 min from which total daily distance traveled was calculated. Visual counts for bite rate were obtained from collared cows over 8 d. Coordinate data, daily bite rate, BW, and BCS were analyzed as repeated measures using a mixed model, which included RFI group, day, and RFI group × day as fixed effects and cow within RFI group as the random effect. Change in BW and BCS were analyzed by ANOVA with RFI group as the main effect. Cow BCS and BW differed for both day (P < 0.0001) and day x RFI (P < 0.05). Body condition was less in LRFI cows at the beginning (5.8 +/- 0.13 vs 6.2 ± 0.14 BCS), but similar to HRFI at the end of the study (4.6 +/- 0.13 vs 4.6 +/- 0.14). Body weight for the different RFI cows did not differ (P = 0.197) prior to going to range. However, BW-change and BCS-change differed (P = 0.05) among RFI groups. Not only did the LRFI cows lose less BW (-50.0 +/- 5.41 kg vs -66.6 +/- 5.78 kg) over the trial, they also were less variable with respect to BW loss. Cows did not differ (P > 0.21) by RFI for daily traveled distance or bite rate, but day was significant (P < 0.0001) with cows increasing bite rate as the season of year progressed (55.2 +/- 5.63 bites/min for d 4 vs 84.8 +/- 5.32 bites/min for d 21) and increasing daily traveled distance as snow storms occurred. Although LRFI cows were leaner than HRFI cows at the commencement of the project, they loss less BW and functioned competitively in a late season rangeland environment.