|SPRINKLE, JAMES - University Of Idaho|
|Taylor, Joshua - Bret|
|ROBERTS-LEW, MEGAN - University Of Idaho|
|HALL, JOHN - University Of Idaho|
Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/18/2016
Publication Date: N/A
Interpretive Summary: Does it bug you to see someone not gain any weight while you do, especially when you know that you both eat the same amount of food? Well, in livestock production we get a little irritated at livestock that don’t gain weight when eating the same amount of feed as an animal that’s gaining. It’s all a matter of efficiency. We strive to select more efficient animals to reduce the greatest cost of livestock production, which is feed. Identifying efficient livestock is generally conducted in a pen, while body weight and the feed eaten are monitored regularly. These methods do a decent job at predicting efficient livestock in a small pen where movement is limited. But, do predictions made in a pen describe what’s going on with a cow on open range? We recently set out to study what one predictor of efficiency – the residual feed intake (RFI) method – can tell us about 2-year-old pregnant cows grazing extensive rangelands during early winter. Before grazing started, our cows that were predicted as “efficient” were leaner than cows that were predicted to be “less efficient.” Regardless of being leaner, efficient cows over the course of the 3-month grazing period lost less weight and body condition than the less efficient cows. In fact, there were fewer extremes in weight loss for the efficient group compared with the less efficient group. This indicated to us that the RFI method for predicting efficiency may be useful in identifying cows that best fit a rangeland environment. However, we concede that further studies are needed to determine if the leaner cows predicted to be “efficient” can survive in a rangeland environment while nursing young calves.
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 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.