Grazing ArithmeticGrazing Arithmetic

Dennis HancockExtension Forage Specialist

UGA – Dept. of Crop and Soil Sciences

Dennis HancockExtension Forage Specialist

UGA – Dept. of Crop and Soil Sciences

2009 Georgia Grazing School

Grazing PressureGrazing Pressure

Productivity Per Animal vs. Per Acre

Productivity Per Animal vs. Per Acre

Product animal

Product animal

Undergrazing Overgrazing

Undergrazing Overgrazing

Grazing PressureGrazing Pressure

Undergrazing Overgrazing

Undergrazing Overgrazing

Productivity Per Animal vs. Per Acre

Productivity Per Animal vs. Per Acre

Product animal

Product animal

Product acre

Product acre

O

pti

mum

Opti

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Stocking Rate vs. DensityStocking Rate vs. DensityStocking Rate• Animals per acre over all acres and a period

of time (e.g., months, a season, a year)

675 acres

338 cows

2 acres

1 cow

Stocking Rate vs. DensityStocking Rate vs. Density

338 cows

22.5 acres

1 acre

15 cows

Stocking Density• Animals per acre at any one point in time

(e.g., within a given paddock)

Basic Grazing Numbers

Basic Grazing Numbers

• Animal Data Animal Weight (lbs) Rate of Dry Matter Intake (DMI,

%) Head

• Grazing Data Rest Period (d) Days in a Given Paddock (d) Number of Paddocks Grazing Efficiency (%) Paddock Size (acres)

• Production Data Acres Available (acres) Available Foragebefore (lbs/acre) Available Forageafter

Available Foragediff

Stocking Rate Stocking Density

AvailableForage

ForageNeed

Logistics

Basic Grazing Numbers

Basic Grazing Numbers

• Animal Data Animal Weight (lbs) Rate of Dry Matter Intake (DMI,

%) Head

• Grazing Data Rest Period (d) Days in a Given Paddock (d) Number of Paddocks Grazing Efficiency (%) Paddock Size (acres)

• Production Data Acres Available (acres) Available Foragebefore (lbs/acre) Available Forageafter

Available Foragediff

Stocking Rate Stocking Density

AvailableForage

ForageNeed

Logistics

Estimating Forage NeedEstimating Forage NeedBy % of body weight (Table Data):

Animal Class Forage Intake Range(DM as a % of b.w.)

Dairy cow 2.0 - 4.0Dairy heifer 2.2 - 2.8Bull 1.5 - 1.9Beef, cow (dry) 1.7 - 2.0Beef, cow (late gest.) 1.8 - 2.1Beef, cow (early lact.) 1.9 - 2.4Beef, stocker (steer) 2.4 - 3.2Beef, stocker (heifer) 2.2 - 2.6Beef, finishing 2.3 - 2.5Beef, replacement heifers 2.0 - 2.4Sheep, ewes (dry) 1.5 - 2.0Sheep, ewes (late gest.) 2.2 - 3.2Sheep, ewes (early lact.) 3.0 - 4.8Horse, Mature (maint.) 1.0 - 2.0Horse, Mature (late gest.) 1.0 - 2.0Horse, Mature (early lact.) 1.3 - 2.6Horse, Weanling (< 600 lbs) 2.3 - 2.8Horse, Yearling (600-1000 lbs) 2.0 - 2.3Goat, nanny (dry) 1.5 - 2.0Goat, nanny (late gest.) 2.2 - 3.2Goat, nanny (early lact.) 2.8 - 4.8

Estimating Forage NeedEstimating Forage NeedBy % of body weight (Table Data):

Animal Class Forage Intake Range(DM as a % of b.w.)

Dairy cow 2.0 - 4.0Dairy heifer 2.2 - 2.8Bull 1.5 - 1.9Beef, cow (dry) 1.7 - 2.0Beef, cow (late gest.) 1.8 - 2.1Beef, cow (early lact.) 1.9 - 2.4Beef, stocker (steer) 2.4 - 3.2Beef, stocker (heifer) 2.2 - 2.6Beef, finishing 2.3 - 2.5Beef, replacement heifers 2.0 - 2.4Sheep, ewes (dry) 1.5 - 2.0Sheep, ewes (late gest.) 2.2 - 3.2Sheep, ewes (early lact.) 3.0 - 4.8Horse, Mature (maint.) 1.0 - 2.0Horse, Mature (late gest.) 1.0 - 2.0Horse, Mature (early lact.) 1.3 - 2.6Horse, Weanling (< 600 lbs) 2.3 - 2.8Horse, Yearling (600-1000 lbs) 2.0 - 2.3Goat, nanny (dry) 1.5 - 2.0Goat, nanny (late gest.) 2.2 - 3.2Goat, nanny (early lact.) 2.8 - 4.8

Beef, cow (dry) 1.7 - 2.0

Animal Class Forage Intake Range(DM as a % of b.w.)

Estimating Forage NeedEstimating Forage NeedBy % of body weight (Table Data):

Beef, cow (dry) 1.7 - 2.0

Animal Class Forage Intake Range(DM as a % of b.w.)

2400 lbs/d=1200 lb cow 2.0%/hd/d 100 hdx x

Daily Forage Need - Calculator

Basic Grazing Numbers

Basic Grazing Numbers

• Animal Data Animal Weight (lbs) Rate of Dry Matter Intake (DMI,

%) Head

• Grazing Data Rest Period (d) Days in a Given Paddock (d) Number of Paddocks Grazing Efficiency (%) Paddock Size (acres)

• Production Data Acres Available (acres) Available Foragebefore (lbs/acre) Available Forageafter

Available Foragediff

Stocking Rate Stocking Density

AvailableForage

ForageNeed

Logistics

Rest Period and Occupancy depend on the Growth Curve

Days of Growth

0 5 10 15 20 25 30 35 40 45 50

For

age

Mas

s(d

ry lb

s/a

cre)

0

2000

4000

6000

8000

10000

120001st Growth Period2nd Growth Period3rd Growth Period4th Growth Period

Available Forage(dry mass/unit

area)

Grazing Rules of ThumbGrazing Rules of Thumb

Crop

Target Height (inches)Recommended

Rest Period (days)

Begin Grazing

End Grazing*

Alfalfa (grazing types) 10-16 2-4 15-30Annual Ryegrass 6-12 3-4 7-15Bahiagrass 6-10 1-2 10-20Bermudagrass 4-8 1-2 7-15Clover, White 6-8 1-3 7-15Clovers, Other 8-10 3-5 10-20Orchardgrass 8-12 3-6 15-30Pearl millet 20-24 8-12 10-20Small grains 8-12 4 7-15Sorghum/sudan 20-24 8-12 10-20Switchgrass 18-22 8-12 30-45Tall Fescue 4-8 2-3 15-30

* Height at end of grazing should take into consideration lower quality forage.

Paddock NumberPaddock NumberHow many paddocks should I use?• Ideally, one should first consider the

needs of the grass. How much rest period is needed? How long should I keep them in a

paddock? i.e., how many days between

rotations?Number of Paddocks

= Days of Rest Days of Grazing

+ 1

9 Paddocks= + 124 days of rest 3 days of grazing

Paddock SizePaddock SizeHow big should my paddocks be?• This is where it all comes together…

But, there’s one element we still need to measure.

We’ll come back to that! In the meantime, let’s refresh our

memory on grazing efficiency.

PaddockSize

Animal Weight x %DMI x Head x Days in PaddockAvailable Foragediff x Grazing Efficiency %

=

Mechanical

Hay 30-70%

Silage 60-85%

Green Chop 70-95%

Efficiencies of Grazing and Mechanized Harvest

Efficiencies of Grazing and Mechanized Harvest

Method Efficiency

Grazing

Continuous Stocking 30-40%

Slow Rotation (3-4 paddocks) 50-60%

Moderate Rotation (6-8 paddocks)

60-70%

Well-managed MiG 70-80%

Basic Grazing Numbers

Basic Grazing Numbers

• Animal Data Animal Weight (lbs) Rate of Dry Matter Intake (DMI,

%) Head

• Grazing Data Rest Period (d) Days in a Given Paddock (d) Number of Paddocks Grazing Efficiency (%) Paddock Size (acres)

• Production Data Acres Available (acres) Available Foragebefore (lbs/acre) Available Forageafter

Available Foragediff

Stocking Rate Stocking Density

AvailableForage

ForageNeed

Logistics

The Primary CalculationsThe Primary Calculations

PaddockSize

Animal Weight x %DMI x Head x Days in PaddockAvailable Foragediff x Grazing Efficiency %

=

= Days of Rest Days in Paddock

+ 1Number of Paddocks

AvailableAcres

= xPaddockSize

Number of Paddocks

Grazier's Arithmetic: A Grazing Calculator

Tracking Forage Availability

Tracking Forage Availability

• Rising plate meter (falling plate)

• Rising plate meter (falling plate)

Tracking Forage Availability

Tracking Forage Availability

11002500

Tracking Forage Availability

Tracking Forage Availability

Grazing StickGrazing StickSTAND RATING

Forage Thin Good Thick

--- (dry lbs/acre/inch) ---

Bermudagrass 80-200 200-300 300-450

Fescue 50-150 150-200 200-300

Fes. + Clover 50-125 125-200 200-275

Ryegrass 100-200 200-250 250-350

Small grain 100-150 150-200 200-300

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500

1000

1500

2000

2500

3000

3500

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

Paddock No. or ID

Dry

Mat

ter

(lbs/

acre

)Grazing “Wedge” – May

15Grazing “Wedge” – May

15

0

500

1000

1500

2000

2500

3000

3500

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

Paddock No. or ID

Dry

Mat

ter

(lbs/

acre

)

Grazing “Wedge” – Dec. 1Grazing “Wedge” – Dec. 1

Grazing Wedge Calculator

ResourcesResources

ResourcesResources

Grass Productivity – Andre Voisin, 1959.On Google Books or available for purchase

Questions?www.georgiaforages.co

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