12 - justin derner - grazing systems for beef...
TRANSCRIPT
Grazing Systems for Beef Production: What are the Benefits?
Justin Derner
Cheyenne, WY
Road Map
Fundamental questions Evidence-based
assessments Long-term experiment
Literature review Role of Grazing
Systems Conclusions Questions/Discussion
Definition
Grazing system: Movement of livestock between two or more subunits of rangeland such that alternating periods of grazing and no grazing (rest) occur within a single growing season (Heitschmidt and Taylor 1991)
Intensive short duration grazing systems implemented by managers and studied by researchers since 1980 (Briske et al. 2008)
Why Implement Grazing System?
Enhanced plant and animal production Increased intensity of management Increased flexibility of operation Facilitate animal management and
veterinary care Personal goals and values Adaptive management applications Attainment of specific outcomes
Fundamental Questions
Managers have found that rotational grazing systems can work for diverse management purposes….but, scientific experiments have demonstrated that they do not necessarily work for specific ecological purposes.
Contradictory…, but can be reconciled by giving equal importance to biophysical variables and to human variables (goal setting, experiential knowledge and decision-making)
Fundamental Questions
Scientific evidence refuting ecologicalbenefits of rotational grazing is robust, but narrowly-focused (intentionally excluded human variables)
Grazing management and grazing systems are two different issues – separation of the human dimensions and the implementation of practice/infrastructureaspects
RESULTS FROM A LONG-TERM GRAZING EXPERIMENT
NORTHERN MIXED-GRASS PRAIRIE
High Plains Grasslands Research Station
15 inch average precipitation
Mixed-grass prairie 1380 pounds/acre
average forage production
Elevation from 6200-6400 feet
128 day growing season
Treatments
Stocking Rates Moderate 7.5 acres/steer
Heavy 5.5 acres/steer
Grazing Systems Season-long June-mid October
Short-duration 8 paddocks 4 cycles of 2, 3, 5 and 7 days
Response Variables
Yearling beef cattle weight gains Weighed prior to and following grazing season
Vegetation production Harvested in late July/early August from temporary exclosures
Study Notes
Started in 1982, results through 2006 reported Longest known grazing system X stocking rate study in North America
No grazing in 2000 and 2002 Severe droughts
Grazing seasons shortened in 1994 and 2006
Livestock Weight Gains
Stocking RateModerate Heavy Season-long Short-durationAv
erag
e D
aily
Gai
n (p
ound
s/he
ad/d
ay)
1.5
1.6
1.7
1.8
1.9
2.0
2.1
2.2 1991-2006 Dry Average Wet
Grazing System
*
* * ** *
Derner et al. 2008
Vegetation Production
Stocking RateModerate Heavy Season-long Short-durationVe
geta
tion
Prod
uctio
n (p
ound
s/ac
re)
500
1000
1500
2000
25001991-2006 Dry Average Wet
Grazing System
Derner and Hart 2007
LITERATURE REVIEW
USDA-NATURAL RESOURCE CONSERVATION SERVICE (NRCS),
CONSERVATION EFFECTS ASSESSMENT PROJECT (CEAP)
Plant and Animal Responses
Briske, Derner, Milchunas, Tate – CEAP Prescribed Grazing Chapter, in press
Plant and Animal Production
Briske et al. 2008
Vegetation Composition
Briske, Derner, Milchunas, Tate – CEAP Prescribed Grazing Chapter, in press
Vegetation Composition
Briske, Derner, Milchunas, Tate – CEAP Prescribed Grazing Chapter, in pres
Forage Responses
Forage quality: Inconsistent responses to grazing system
short, periodic non-grazing periods do not always coincide with favorable growth conditions
Livestock selectivity Grazing system does not override livestock preference for site selectivity Rainfall variability and associated lack of
predictability of plant growth appear to override the potential benefit derived from the redistribution of grazing pressure in space and time
Tiller Defoliations
Rotational grazing may not control the frequency and intensity of plant defoliation as effectively as often assumed
Difficult to obtain high percentage of tiller defoliations (>80%) before multiple defoliations occur within a single grazing period (Jensen et al. 1990)
Soil Hydrologic Function
Grazing system has similar or improved soil hydrologic function at moderate stocking rates
Soil hydrologic functions degraded by heavy stocking generally cannot be overcome by grazing system alone
Soil hydrologic function can recover with prolonged (>1 yr) rest
Wildlife
Grazing system generally has neutral effects on grassland birds Longer rests often beneficial to increase structural aspects of vegetation
Deer generally are negatively affected by grazing systems
Elk not affected by grazing system, but are sensitive to stocking rate
Generally, many false claims and few valid studies in the literature
General Conclusions from Experimental Evidence
Grazing system does not promote primary or secondary production compared to continuous grazing Consistent with previous reviews
Sampson 1951, Heady 1961, Van Poolen and Lacey 1979, O’Reagain and Turner 1992
Stocking rate and weather variation account for much of the variability associated with plant and animal production
WHAT IS THE ROLE OF GRAZING SYSTEMS?
WHY DO PRODUCERS USE THEM?
Role of Grazing Systems
Experimentally it is extremely difficult to mimic livestock movements and defoliation patterns used by managers
Grazing systems research has carefully evaluated ecological responses, with vast majority of results indicating no clear advantage of any one grazing system over another in terms of ecological benefits
Role of Grazing Systems
Contributions of grazing systems to broad conservation goals and ecosystem services have yet to be evaluated
Not only sufficient to evaluate whether or not grazing system is effective, but why is it effective? Place emphasis on facilitating practices or adaptive management skills?
Role of Grazing Systems
Importance of effective adaptive management is widely acknowledged but poorly studied Management goals, abilities and opportunities, personal goals and values (human dimensions aspects)
Research and monitoring on ranch scale operations is needed e.g., Pinchak et al. 2010, Ansley et al. 2010, Teague et al. 2010
Grazing System X Management
What does a grazing system do for grazing management? Facilitates forage inventory, animal care, and monitoring?
Facilitates greater managerial control and responsiveness?
Management skills vs. rules of thumb? Can grazing systems be helpful to
management if they do not increase production?
