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WS Grazing behavior and production characteristics among cows differing in residual feed intake while grazing late season Idaho rangeland
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 x Angus (LRFI = 16; HRFI = 14) 2-year-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 travel 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 x 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 = 0.1974) 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 distance travelled 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 distance travelled 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.
Keywords: Beef Cattle, Grazing behavior, Rangeland, Residual feed intake