the effect of grazing intensity on the grasslands and cattle performance v8

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


2006

2007

2008

2009

201020-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


2006

2007

2008

2009

2010

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

10

20

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Year1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010

Pe

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in 2

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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

UU

U

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U U

U

U

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HH H

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HE

E

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E

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EE

E E EE E

E E E EE

E E E E E E

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50

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Year1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010

Pe

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in 2

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25

cm

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U U U UU

UU

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U UU

U UU

UU

L L

L L

L L

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L

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L LL

L

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MM

M MM

M

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M

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HH

H H H H H

H H

H HH

H

H

H

H H

H

HH

H H

H

E EE

E E

E

E

E E

E E

E EE

E E E

E

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E EE

0

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Year1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010

Pe

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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

M

MM M

H H H H H H H H H H H HH

H H H H HH H

HH

H

E E E E E E E E E E E

E E E

E

E E E

E

E

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E

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Year1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010

Pe

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in 5

X 5

cm

fra

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U U

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U

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U

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U

U

UU

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U U

U

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L L

L

L

L

L

L

LL L

LL

L LL L L L

L

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L

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M MM

M

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M

MM

MM M

M M

MM M

M

M

M

MM

M

HH

HH

H

H

H H H H

H H HH

HH

H

H

H H

H

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HE

E

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E E

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EE

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




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

300

400

500

Year1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010

2P

lan

ts/M


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

0

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Year1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010

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in 2

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cm

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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

MM

M M

MM

MM

MM

M

M

M

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

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Year1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010

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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

EE

E

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

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in 2

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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

M

H H H H

H

H

HH

HH

H

H

H

HH

H

H

HH

H

H

H

H

E E E E

E

E

E

E

E

E

E

E

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E

E

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E

E

E

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.

the effect of grazing intensity on the grasslands and cattle performance v8

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