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