The effect of grazing intensity on grasslands and cattle performance in south-central North DakotaBob Patton, Paul Nyren, and Anne Nyren
North Dakota State University - Central Grasslands Research Extension Center, Streeter ND
A long-term grazing intensity study began at CGREC in 1989 to determine the ecological and economic effects of season-long cattle grazing at different intensities. Five treatments - no grazing, light, moderate, heavy, and extreme grazing - are each replicated three times. Pastures are approximately 30 acres each. The no grazing treatment consists of six 0.3-acre exclosures. Pastures are stocked so that when the cattle are removed in the fall, about 65, 50, 35, and 20% of the forage produced in an average year remains on the light, moderate, heavy, and extreme grazing treatments respectively.
The two most common ecological sites, loamy and loamy overflow, are monitored. Forage production on the loamy site is highest under the light grazing treatment. On the loamy overflow site, production does not differ between light, moderate, and heavy, but ungrazed and extreme treatments produce significantly less forage.
A total of 164 species have been found on the loamy sites and 62 have shown a response to grazing based on frequency, density, or basal cover. Of the 172 species on the loamy overflow sites, 53 have responded to grazing. These responses include increasing or decreasing with increased grazing pressure, benefiting from moderate grazing, or invading (only appearing after heavy grazing). Of the species responding to grazing (30-40% of the total), the majority are favored by a moderate or heavy level of grazing.
Since 1990, average daily gain and animal body condition scores have decreased with increasing grazing intensity. Initially, gain/ton of available forage increases as the stocking rate increases, but then declines at higher stocking rates.
We cannot predict which stocking rate will give the maximum gain/ton of forage in a particular year. However, at 2.39 AUM/ton, gain/ton from 1991-2010 would have averaged 75.7 lbs/ton. If cattle prices were consistent, then return/ton would peak at a stocking rate somewhere below maximum gain/ton, with the exact point depending on carrying costs. The change in cattle prices over the season determines the stocking rate with the maximum return/ton. The stocking rate with the maximum return/ton over the last 20 years would be 1.74 AUM/ton, with an average annual return of $28.24/ton.
Average above ground biomass production by grazing treatment on loamy ecological sites from 1992 to 2010.
Above ground biomass (lbs/acre)
Treatment
Beginning
of season
Middle of
season
Peak
yield
End of
season
Ungrazed 1,253 b1 2,448 b 2,728 c 2,592 c
Light 1,314 a 2,765 a 3,168 a 3,071 a
Moderate 1,178 c 2,535 b 2,941 b 2,844 b
Heavy 901 d 2,148 c 2,421 d 2,339 d
Extreme 732 e 1,821 d 2,189 e 2,150 d
LSD (0.05) 59 142 183 196
1Means in the same column followed by the same letter are not significantly different at P=0.05.
Average above ground biomass production by grazing treatment on loamy overflow ecological sites from 1993 to 2010.
Above ground biomass (lbs/acre)
Treatment Beginning of season
Middle of season
Peak yield
End of season
Ungrazed 1,002 b1 3,205 c 3,350 b 2,928 b
Light 1,156 a 3,890 a 4,173 a 3,936 a
Moderate 1,230 a 3,666 ab 4,116 a 3,994 a
Heavy 1,216 a 3,566 b 3,935 a 3,901 a
Extreme 841 c 2,211 d 2,606 c 2,524 c
LSD (0.05) 80 252 262 271
1Means in the same column followed by the same letter are not significantly different at P=0.05.
Average daily gains, gains per acre, gains per ton of forage and condition scores from different stocking intensities.
Desired Grazing Intensity
Average Daily Gains (lbs./head/day)
2006 2007 2008 2009 2010 Average 1991-2010
Light 0.57 1.36 1.75a1 2.05a 1.54 1.39a
Moderate 0.62 1.22 1.58ab 1.99a 1.29 1.28a
Heavy 0.48 1.33 1.35b 1.48b 1.09 1.10b
Extreme 0.13 1.16 0.95c 1.09b 1.02 0.80c
LSD (0.05) NS2 NS 0.38 0.42 NS 0.14
Average Gain (lbs./acre)
2006 2007 2008 2009 2010 Average 1991-2010
Light 11.01 44.41c 39.73b 47.37b 47.58 30.02c
Moderate 20.82 69.27bc 68.61ab 90.63a 68.95 55.19b
Heavy 20.77 107.47ab 82.15a 92.72a 84.55 76.45a
Extreme 7.48 122.96a 76.10a 90.79a 104.70 81.42a
LSD (0.05) NS 42.67 29.04 34.31 NS 10.30
Average Gain (lbs./ton of forage)
2006 2007 2008 2009 2010
Average 1991-2010
Light 9.83 23.19c 27.11c 33.80b 19.01c 19.53d
Moderate 19.81 39.26bc 51.13b 62.10ab 31.24bc 35.19c
Heavy 26.25 64.56ab 70.51ab 77.54a 52.54ab 59.21b
Extreme 14.00 82.26a 78.22a 92.90a 64.87a 73.44a
LSD (0.05) NS 27.81 22.96 33.78 27.37 8.66
Condition Score
2006 2007 2008 2009 2010
Average 1994-2010
Light 5.08 5.60 6.99a 5.77 5.24 5.47a
Moderate 5.17 5.50 6.51b 5.52 5.19 5.36ab
Heavy 5.02 5.54 6.38b 5.46 5.16 5.24b
Extreme 4.81 5.41 5.82c 4.97 5.05 4.93c
LSD (0.05) NS NS 0.39 NS NS 0.18 1Means in the same column followed by the same letter are not significantly different at p=0.05. 2Means not significantly different.
20 year ave.2009
2007
2010
20082006
0.0
0.5
1.0
1.5
2.0
2.5
AUMs/Ton of Forage0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
2006
2007
2008
2009
2010
20-yr. ave.
upper c.i. of 20-yr. ave.
lower c.i. of 20-yr. ave.
trial for 2006 to 2010 and the 20-year average with 95 percent confidence intervals.
Relationships between average daily gain and stocking rate on the grazing intensity
Pounds/
Head/D
ay
Lig
ht
Modera
te
Heavy
Ext
rem
e
YEAR
2009 20 year ave.
2007
2010
20082006
-25
0
25
50
75
100
125
150
175
200
225
AUMs/Ton of Forage0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
2006
2007
2008
2009
201020-yr. ave.
upper c.i. of 20-yr. ave.
lower c.i. of 20-yr. ave.
for 2006 to 2010 and the 20-year average with 95 percent confidence intervals.
Relationships between gain/ton and stocking rate on the grazing intensity trial
Pounds\
Ton
Lig
ht
Modera
te
Heavy
Optim
um
Ext
rem
e
YEAR
20 year ave.2009
2007
2010
20082006
-100
-80
-60
-40
-20
0
20
40
60
80
100
120
140
AUMs/Ton of Forage0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
2006
2007
2008
2009
2010
20-yr. ave.
upper c.i. of 20-yr. ave.
lower c.i. of 20-yr. ave.
confidence intervals.
the grazing intensity trial for 2006 to 2010 and the 20-year average with 95 percent
Relationships between returns to land, labor and management and stocking rate on
Dolla
rs/T
on
Lig
ht
Modera
te
Optim
um
Heavy
Ext
rem
e
YEAR
Comparison of gain in pounds per ton of forage from selected stocking rates.
A B C
Stocking rate in AUMs/ton of forage that would result in the maximum gain/ton in each year.
Stocking rate in AUMs/ton of forage that if held constant would result in the maximum gain/ton over the twenty-year period.
Gain/ton over the twenty-year period if stocking rate were held constant at 0.69 AUMs/ton of forage, the average of the moderate treatment over this period.
Year AUMs/ton of forage Gain/ton
AUMs/ton of forage Gain/ton
AUMs/ton of forage Gain/ton
1995 2.52 60.3 2.39 60.1 0.69 28.7 1996 2.90 62.8 2.39 60.8 0.69 25.8 1997 2.30 95.4 2.39 95.2 0.69 46.6 1998 2.10 75.6 2.39 74.1 0.69 40.2 1999 3.46 108.3 2.39 97.6 0.69 37.1 2000 2.75 70.9 2.39 69.7 0.69 30.4 2001 * 2.39 104.2 0.69 36.6 2002 2.65 80.6 2.39 79.9 0.69 40.6 2003 * 2.39 73.8 0.69 28.7 2004 1.50 80.1 2.39 43.5 0.69 49.5 2005 2.43 48.3 2.39 48.3 0.69 22.8 2006 3.08 35.9 2.39 34.2 0.69 15.3 2007 * 2.39 106.4 0.69 34.7 2008 1.89 80.4 2.39 74.3 0.69 46.1 2009 2.25 95.7 2.39 95.4 0.69 53.7 2010 1.85 65.6 2.39 59.4 0.69 37.8
20-year avg. 2.44 77.4 2.39 75.7 0.69 36.9
* The regressions for 2001, 2003 and 2007 were not suitable to project the peak in gain/ton.
0
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Year1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010
Pe
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Treatment Ungrazed Light Moderate Heavy ExtremeU U U L L L M M M H H H E E E
UU U U
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Year1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010
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Treatment Ungrazed Light Moderate Heavy ExtremeU U U L L L M M M H H H E E E
U U U UU
UU
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U UU
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UU
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L L
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Year1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010
Pe
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Treatment Ungrazed Light Moderate Heavy ExtremeU U U L L L M M M H H H E E E
U U U U U U U U U U U U U U U U U UU U U U UL L L L L L L L L L L
L L L L L L L L L L L LM M M M M M M M M M M M M M M M M MM
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H H H H H H H H H H H HH
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Year1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010
Pe
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in 5
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Treatment Ungrazed Light Moderate Heavy ExtremeU U U L L L M M M H H H E E E
U U
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E
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E
Abstract
Treatment layout
On the loamy ecological site, tforage production is on the light treatment.
he greatest
On the loamy overflow ecological site, forage production does not differ between the light, moderate, and heavy treatments, but ungrazed and extreme produce significantly less forage.
Forage Production
Plant Community Dynamics
Loamy Sites
Of the 164 plant species on loamy ecological sites, 62 have shown a response to grazing (listed in order of dominance).
Loamy Overflow Sites
Of the 172 plant species on loamy overflow ecological sites, 53 have shown a response to grazing.
Livestock ResponseAverage daily gain and condition scores decrease as grazing intensity increases. Gain per ton of forage initially goes up as grazing intensity increases, but there is a point beyond which gain per ton decreases with increasing grazing intensity.
If cattle prices were constant, then return/ton would peak at a stocking rate somewhere below maximum gain/ton, with the exact point depending on carrying costs. The change in cattle prices over the season determines the stocking rate with the maximum return/ton. The stocking rate with the maximum return/ton over the last 20 years would be 1.74 AUM/ton, with an average annual return of $28.24/ton.
ConclusionsAfter 21 years, this study has demonstrated that:
ŸBiomass production is greatest with a light or moderate stocking rate.
ŸPlant species diversity is lowest under no grazing and increases with grazing intensity, although many of the species that increase under extreme grazing are weedy or invasive.
ŸIndividual animal daily gains and condition scores decrease with increasing grazing intensity.
ŸGain per ton of available forage peaks at around 2.39 AUM/ton of forage.
ŸEconomic return peaks at around 1.74 AUM/ton of forage.
For more information, visit the CGREC website:
www.ag.ndsu.edu/CentralGrasslandsREC/
Economics
2.3 AUM/ton of forage
1.3 AUM/ton of forage
0.7 AUM/ton of forage
0.3 AUM/ton of forage
Species that decrease under grazing:
Poa pratensis - Kentucky bluegrassLotus purshianus - deer vetchHelianthus pauciflorus - stiff sunflowerArtemisia absinthium - wormwoodPsoralea esculenta - breadroot scurf-pea
An example: Helianthus pauciflorus
Some species favored by moderate grazing:
Artemisia ludoviciana - cudweed sagewortOligoneuron rigidum - stiff goldenrodStipa curtiseta - western porcupine grassCirsium flodmanii - Flodman's thistleRatibida columnifera - prairie coneflowerBromus inermis - smooth brome
An example: Cirsium flodmanii
Species that appear only after heavy grazing:
Agrostis hyemalis - ticklegrassMedicago lupulina - black medicJuncus interior - inland rushPolygonum ramosissimum - bushy knotweedTrifolium repens - white clover
An example: Medicago lupulina
Species that decrease under grazing:
Symphoricarpos occidentalis - buckbrushBromus inermis - smooth bromeHelianthus pauciflorus - stiff sunflowerRosa arkansana - prairie roseLiatris ligulistylis - round-headed blazing star
An example: Bromus inermis
0
100
200
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Year1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010
2P
lan
ts/M
Treatment Ungrazed Light Moderate Heavy ExtremeU U U L L L M M M H H H E E E
U U U U U
U
U
U
U U U
U
UU U
U U UU U U U
L L LL L
L
L
L LL
LL
L L L L L
L
L L
L
L
M MM M M
MM
M
M M
M
M
M M MM M
M
M MM
M
H H H H H
H
H
H
HH
H HH
HH
H
H
H
H H
H
H
E E E E E
EE E E E
EE
E E EE E
E
E E
E
E
Some species favored by moderate grazing:
Oligoneuron rigidum - stiff goldenrodAmbrosia psilostachya - western ragweedSolidago canadensis - Canada goldenrodGlycyrrhiza lepidota - wild licoriceSolidago mollis - soft goldenrodCarex lanuginosa - wooly sedge
An example: Oligoneuron rigidum
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Year1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010
Pe
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in 2
5 X
25
cm
fra
me
sTreatment Ungrazed Light Moderate Heavy ExtremeU U U L L L M M M H H H E E E
UU U U U
U
U
U
U
UU
U U
U
UU
U U
U
U UU
U
L L L L L L
L
L L LL
LL L
L
L
L
L
L
LL
L
L
MM
M
M
M
M
M
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M M
MM
MM
MM
M
M
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M M
M
H H H H H
H
H
H
H H
H
H
HH
H
H
H
H
H
H
H
H
H
E EE
EE
E
E
EE E
E
E
EE
E
EE
E
E
E
EE E
Some species that increase under grazing:
Poa pratensis - Kentucky bluegrassSymphyotrichum ericoides - heath asterArtemisia ludoviciana - cudweed sagewortAchillea millefolium - western yarrowCarex inops ssp. heliophila - sun sedgeTaraxacum officinale - common dandelion
An example: Taraxacum officinale
0
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Year1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010
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Treatment Ungrazed Light Moderate Heavy ExtremeU U U L L L M M M H H H E E E
U U U U U U U U U U U U U U U U U U U U U U UL L L L L L L L L L L L L L L L L L L L L L LM M M M M M M M M M M M M M M M M M M M MM
MH H H H H H H H H H H H H H H H H H H H H H HE E E E E E E E E EE E
E
E
E
E
E
E
E
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E
Species that appear only after heavy grazing:
Medicago lupulina - black medicTrifolium repens - white cloverPolygonum ramosissimum - bushy knotweedLithospermum incisum - yellow puccoonLepidium densiflorum - peppergrass
For example: Trifolium repens
Some species that increase under grazing:
Pascopyrum smithii - western wheatgrassCarex inops ssp. heliophila - sun sedgeNassella viridula - green needlegrassAchillea millefolium - western yarrowBouteloua gracilis - blue gramaTaraxacum officinale - common dandelionArtemisia frigida - fringed sagewort
An example: Potentilla pensylvanica
0
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Year1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010
Pe
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fra
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Treatment Ungrazed Light Moderate Heavy ExtremeU U U L L L M M M H H H E E E
U U U U U
U
UU
UU
U UU U U U U U U U
UU
UL L L L L
L
L L L
L
L L L L LL
L L L L L L LM M M M
M
M M
M
M M M
MM
M
M
M
M
M
M
MM
M
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H H H H
H
H
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HH
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HH
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E E E E
E
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Comparison of return to land, labor and management from selected stocking rates.
Stocking rate in AUMs/ton of forage that would result in the maximum returns/ton to land, labor and management in each year.
Stocking rate in AUMs/ton of forage that if held constant would result in the maximum returns/ton to land, labor and management over the twenty-year period.
Returns/ton to land, labor and management over the twenty-year period if stocking rate were held constant at 0.69 AUMs/ton of forage, the average of the moderate treatment over this period.
Year AUMs/ton of forage Dollars/ton
AUMs/ton of forage Dollars/ton
AUMs/ton of forage Dollars/ton
1991 0.42 1.81 1.74 (6.28) 0.69 1.45 1992 * 1.74 80.90 0.69 34.38 1993 1.42 59.35 1.74 56.26 0.69 44.06 1994 0.55 0.95 1.74 (10.82) 0.69 0.79 1995 0.86 0.53 1.74 (4.72) 0.69 0.33 1996 2.57 32.88 1.74 29.31 0.69 14.68 1997 1.13 15.53 1.74 9.60 0.69 12.63 1998 0.63 0.31 1.74 (8.78) 0.69 0.28 1999 3.53 55.20 1.74 40.52 0.69 18.29 2000 2.06 16.15 1.74 15.71 0.69 8.16 2001 * 1.74 40.02 0.69 18.37 2002 0.00 12.93 1.74 (17.39) 0.69 (3.56) 2003 * 1.74 74.37 0.69 35.15 2004 1.98 83.72 1.74 82.30 0.69 42.66 2005 1.25 10.83 1.74 8.84 0.69 8.31 2006 1.76 57.41 1.74 57.40 0.69 30.28 2007 * 1.74 54.65 0.69 23.56 2008 1.72 51.30 1.74 51.29 0.69 31.22 2009 1.22 18.82 1.74 15.87 0.69 15.87 2010 0.90 9.67 1.74 (4.25) 0.69 8.78
20-year avg. 1.38 26.71 1.74 28.24 0.69 17.28
* The regressions for 1992, 2001, 2003 and 2007 were not suitable to project the peak in returns to land, labor and management.