Evaluation of APEX cattle weight gain component for grazing decision-support in the Western Great Plains

Authors: CHENG, GONG - Colorado State University; Harmel, Daren; Ma, Liwang; Derner, Justin; Augustine, David; BARTLING, PATRICIA - Retired ARS Employee; FANG, Q - Qingdao Agricultural University; WILLIAMS, JIMMY - Texas A&M University; ZILVERBERG, CODY - Producer; BOONE, RANDY - Colorado State University; YU, Q - Agri Food - Canada

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/25/2022
Publication Date: 5/1/2022
Citation: Cheng, G., Harmel, R.D., Ma, L., Derner, J.D., Augustine, D.J., Bartling, P., Fang, Q., Williams, J., Zilverberg, C., Boone, R., Yu, Q. 2022. Evaluation of APEX cattle weight gain component for grazing decision-support in the Western Great Plains. Rangeland Ecology and Management. 82:1-11. https://doi.org/10.1016/j.rama.2022.01.005.
DOI: https://doi.org/10.1016/j.rama.2022.01.005

Interpretive Summary: Rotational grazing studies have produced mixed results related to animal performance (weight gain), which has contributed to producer uncertainty regarding grazing management decisions. To enhance decision-support for producers, we improved algorithms in the APEX model to better represent cattle weight gain in real-world rangeland conditions under two grazing management strategies. Simulated weight gain and related forage effects were evaluated with experimental data from 2014-2018 under two grazing strategies: Traditional Rangeland Management (TRM) with continuous season-long grazing stocked at a moderate level and Collaborative Adaptive Rangeland Management (CARM) grazing with one large herd rotated using a sequence developed by a stakeholder group with movement between pastures driven by pre-determined decision triggers. For each grazing strategy, yearling steers grazed from mid-May to October on 10, 130 ha pastures. With the APEX modifications, daily weight gain was adequately simulated for both continuous (TRM) grazing and management intensive rotational (CARM) grazing. Dry matter intake, total digestible nutrients, and temporal distribution of dry matter intake were shown to be the primary influences of cattle performance (weight gain). Once shown to be accurate, we used APEX to evaluate several management alternatives (i.e., stocking rate, rotation interval, and rotation decision criteria) to showcase its decision support capabilities. These important enhancements increase the utility of APEX in semiarid environments such as the western Great Plains in providing science-based rangeland decision support to ranchers, agency land managers, and policy makers.

Technical Abstract: Rotational grazing studies have produced mixed results related to cattle weight gain, which has contributed to rancher uncertainty regarding grazing management decisions. Thus, we improved the APEX model to better represent cattle weight gain in real-world rangeland conditions under two grazing management strategies. Simulated weight gain and related forage effects were evaluated with experimental data from 2014-2018 under two grazing strategies: Traditional Rangeland Management (TRM) with continuous season-long grazing stocked at a moderate level and Collaborative Adaptive Rangeland Management (CARM) grazing with one large herd rotated using a sequence developed by a stakeholder group with movement between pastures driven by pre-determined decision triggers. For each grazing strategy, yearling steers grazed from mid-May to October on 10, 130 ha pastures. With the APEX modifications, daily weight gain was adequately simulated for both continuous (TRM) grazing and management intensive rotational (CARM) grazing. Dry matter intake, total digestible nutrients, and temporal distribution of dry matter intake were shown to be the primary influences of cattle performance (weight gain). Once shown to be accurate, we used APEX to evaluate several management alternatives (i.e., stocking rate, rotation interval, and rotation decision criteria) to showcase its decision support capabilities. These important enhancements increase the utility of APEX in semiarid environments such as the western Great Plains in providing science-based rangeland decision support to ranchers, agency land managers, and policy makers.