PSII-11 Using GPS Data and Daily Weights to Estimate Net Energy for Activity in Yearling Steers. (22nd October 2022) - Vandermark, Logan R
Abstract: Past research has provided the groundwork into determining the impact of daily activity, elevation, and slope on energetic requirements for rangeland cattle. However, there is not a consensus on how to accurately account for this dynamic. Thus, the objectives of this study were to 1) calculate rolling and roughness index and distance traveled respective of elevation change and 2) create a regression analysis from objective 1 and determine differences in precision between the two methods for determining changes in NEmract. This analysis compared two methods to estimate the energetic costs of travel on elevation and slope on net energy for activity (NEmract). The analysis was conducted from a dataset consisting of six herds of yearling steers (n = 127) that grazed native summer pastures from May to August in 2021 at the Cottonwood Field Station (Philip, SD). Pastures were composed primarily of native C3 grasses, Nassella viridula and Pascopyrum smithii, and C4 grasses, Bouteloua gracilis and Buchloe dactyloides. VenceTM collars were set to record GPS fixes at 5-minute intervals. GPS data was coupled with real time weight data collected from Smart Scales (C-Lock Inc, Rapid City, SD) located at the stock tanks within six pastures at three different stocking rates treatments (n = 3, 2 reps per trt). The combination of weight and GPS data allowed for the quantification of how elevation, slope, and daily distance traveled impacted NEmract. The first method to account for daily travel is a quantification of terrain use. This method has two indexes, a roughness index and rolling index, to determine the impact of terrain on grazing distribution. Roughness index is a measure of slope and elevation of an individual animal in comparison to the herd. The rolling index quantifies animal distribution by accounting for distance from water. The second method calculated the distance and elevation changes between successive GPS fixes for individual animals over the course of the summer grazing period. The linear regression was conducted in Program R (P < 0.05) which regressed NEmr plus NEmract calculated using the two methods against back-calculated to NEmr using daily body weight and forage nutrient composition (TDN). The result of this analysis provides levels of precision for different methods when quantifying the daily distance traveled, of steers relative to horizontal and ascending locomotion helping to evaluate trade-offs based on available GPS data (e.g., 5 minutes versus 1 hour recording intervals). Technological advances have allowed unprecedented data collection on individual animals. Results from this study will help refine energetic equations on extensive rangeland systems which is important due to the inherently large travels distances on these production settings.