|Hart, Richard - RETIRED ARS|
|Smith, Michael - UNIVERSITY OF WYOMING|
|James, Waggoner - UNIVERSITY OF WYOMING|
Submitted to: Livestock Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 9, 2007
Publication Date: July 11, 2008
Citation: Derner, J.D., Hart, R.H., Smith, M., James, W.W. 2008. Long-term cattle gain responses to stocking rate and grazing systems in northern mixed-grass prairie. Livestock Science 117:60-69. Interpretive Summary: Stocking rate and grazing system are two primary grazing management practices that can influence livestock gain responses on rangelands. A long-term (25 year) study in the northern mixed-grass rangeland ecosystem demonstrates that individual cattle average daily gain decreases with increasing stocking rate, whereas cattle gain per unit land area increase. Cattle gains were 6% lower with short-duration rotation grazing compared to season-long grazing. These findings demonstrate that rotational grazing is not a superior grazing system compared to season-long grazing.
Technical Abstract: The effects of stocking rate and grazing system on gains of yearling beef cattle grazing rangelands have largely been addressed in short-term (<10 yr) studies, and often stocking rates are confounded within grazing systems with higher stocking rates for short-duration rotational grazing systems compared to season-long grazing. A grazing system (season-long and short-duration rotational grazing) X stocking rate (light: 1.30 ha/steer/month, moderate: 0.63 ha/steer/month, and heavy: 0.46 ha/steer/month) study was initiated in 1982 on northern mixed-grass prairie. Here, we report on the final 16 years (1991-2006) for yearling beef cattle gains. Average daily gains (kg/head/day) across all years with season-long grazing decreased with increasing stocking rate and grazing pressure. Heavy stocking rates reduced average daily gain by 16% and 12% compared to light and moderate stocking rates, respectively. In contrast to average daily gain, beef production (kg/ha) increased with increasing stocking rate and grazing pressure. Cattle gains were reduced by 6% with short-duration rotation compared to season-long grazing over the study period, with differences between systems observed in years with average, but not dry or wet, spring (April+May+June) precipitation. Grazing season gains (kg/head) and beef production both exhibited significant increasing hyperbolic relationships with spring precipitation, with the percentage of variation explained by spring precipitation substantially higher (62-83%) for beef production compared to grazing season gains (32-45%). The influence of spring precipitation on cattle gains suggests that incorporation of these relationships into modeling efforts for strategic planning and risk assessment will assist land managers in better matching forage and animal resources for greater sustainability in this highly variable environment.