2009 Georgia Grazing School:
Grazing Arithmetic
Productivity Per Animal vs. Per Acre
2009 Georgia Grazing School
Grazing Arithmetic
Product
acre
Dennis Hancock
Extension Forage Specialist
UGA – Dept. of Crop and Soil Sciences
Undergrazing
Stocking Rate vs. Density
Stocking Rate
• Animals per acre over all acres and a period of time
Stocking Density
• Animals per acre at any one point in time
 (e.g., months, a season, a year)
 (e.g., within a given paddock)
338 cows
675 acres
338 cows
22.5 acres
1 cow
2 acres
15 cows
1 acre
Basic Grazing Numbers
Estimating Forage Need
• Animal Data
By % of body weight (Table Data):
 Animal Weight (lbs)
 Rate of Dry Matter Intake (DMI, %)
 Head
• Grazing Data
Logistics
Available
Forage





Rest Period (d)
Days in a Given Paddock (d)
Number of Paddocks
Grazing Efficiency (%)
Paddock Size (acres)






Acres Available (acres)
Available Foragebefore (lbs/acre)
Available Forageafter
Available Foragediff
Stocking Rate
Stocking Density
Overgrazing
Grazing Pressure
Stocking Rate vs. Density
Forage
Need
Optimum
Product
animal
• Production Data
Dr. Dennis Hancock
Extension Forage Agronomist
1
Animal Class
Forage Intake Range
Dairy cow
Dairy heifer
Bull
Beef, cow (dry)
Beef, cow (late gest.)
Beef cow (early lact
Beef,
lact.))
Beef, stocker (steer)
Beef, stocker (heifer)
Beef, finishing
Beef, replacement heifers
Sheep, ewes (dry)
Sheep, ewes (late gest.)
Sheep, ewes (early lact.)
Horse, Mature (maint.)
Horse, Mature (late gest.)
Horse, Mature (early lact.)
Horse, Weanling (< 600 lbs)
Horse, Yearling (600-1000 lbs)
Goat, nanny (dry)
Goat, nanny (late gest.)
Goat, nanny (early lact.)
(DM as a % of b.w.)
2.0 - 4.0
2.2 - 2.8
1.5 - 1.9
1.7 - 2.0
1.8 - 2.1
1 9 - 2.4
1.9
24
2.4 - 3.2
2.2 - 2.6
2.3 - 2.5
2.0 - 2.4
1.5 - 2.0
2.2 - 3.2
3.0 - 4.8
1.0 - 2.0
1.0 - 2.0
1.3 - 2.6
2.3 - 2.8
2.0 - 2.3
1.5 - 2.0
2.2 - 3.2
2.8 - 4.8
2009 Georgia Grazing School:
Grazing Arithmetic
Estimating Forage Need
Rest Period and Occupancy depend
on the Growth Curve
By % of body weight (Table Data):
Animal Class
12000
Forage Intake Range
(DM as a % of b.w.)
1.7 - 2.0
Forage M
Mass
(dry lbs/a
acre)
Beef, cow (dry)
1st Growth Period
2nd Growth Period
3rd Growth Period
4th Growth Period
10000
8000
Available
A
il bl F
Forage
6000
(dry mass/unit
area)
2400 lbs/d= 1200 lb cow x 2.0%/hd/d x 100 hd
4000
2000
0
Daily Forage Need - Calculator
0
5
10
15
20
25
30
35
40
45
Days of Growth
Paddock Number
Grazing Rules of Thumb
How many paddocks should I use?
• Ideally, one should first consider the
needs of the grass.
Target Height (inches)
Recommended
Begin Grazing End Grazing* Rest Period (days)
Crop
Alfalfa (grazing types)
10-16
2-4
15-30
Annual Ryegrass
6-12
3-4
7-15
Bahiagrass
6-10
1-2
10-20
Bermudagrass
4-8
1-2
7-15
Clover, White
6-8
1-3
7-15
Clovers, Other
8-10
3-5
10-20
Orchardgrass
8-12
3-6
15-30
Pearl millet
20-24
8-12
10-20
Small grains
8-12
4
7-15
Sorghum/sudan
20-24
8-12
10-20
Switchgrass
18-22
8-12
30-45
Tall Fescue
4-8
2-3
15-30
* Height at end of grazing should take into consideration lower quality forage.
 How much rest period is needed?
 How long should I keep them in a paddock?
 i.e., how many days between rotations?
Number of = Days of Rest + 1
Paddocks
Days of Grazing
9 Paddocks =
24 days of rest + 1
3 days of grazing
Efficiencies of Grazing and
Mechanized Harvest
Paddock Size
How 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
i efficiency.
ffi i
Paddock
Animal Weight x %DMI x Head x Days in Paddock
=
Size
Available Foragediff x Grazing Efficiency %
Dr. Dennis Hancock
Extension Forage Agronomist
2
Method
Efficiency
Grazing
Continuous Stocking
Slow Rotation (3-4 paddocks)
Moderate Rotation (6-8 paddocks)
Well-managed MiG
Mechanical
30-40%
50-60%
60-70%
70-80%
Hay
30-70%
Silage
Green Chop
60-85%
70-95%
50
2009 Georgia Grazing School:
Grazing Arithmetic
The Primary Calculations
Tracking Forage Availability
Available
Paddock x Number of
=
Acres
Size
Paddocks
• Rising plate meter
 (falling plate)
Paddock
Animal Weight x %DMI x Head x Days in Paddock
=
Size
Available Foragediff x Grazing Efficiency %
Number of
Days of Rest
=
+1
Paddocks
Days in Paddock
Grazier's Arithmetic: A Grazing Calculator
Tracking Forage Availability
Tracking Forage Availability
Grazing Stick
Forage
2500
Bermudagrass
Fescue
Fes. + Clover
Ryegrass
Small grain
1100
Grazing “Wedge” – Dec. 1
3500
3500
3000
3000
Dry Matter (lb
bs/acre)
Dry Matter (lb
bs/acre)
Grazing “Wedge” – May 15
STAND RATING
Thin
Good
Thick
--- (dry lbs/acre/inch) --80-200 200-300 300-450
50-150 150-200 200-300
50-125 125-200 200-275
100-200 200-250 250-350
100-150 150-200 200-300
2500
2000
1500
1000
500
2500
2000
1500
1000
500
0
0
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
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
Grazing Wedge Calculator
Dr. Dennis Hancock
Extension Forage Agronomist
3
Paddock No. or ID
2009 Georgia Grazing School:
Grazing Arithmetic
Resources
Resources
Grass Productivity – Andre Voisin, 1959.
On Google Books or available for purchase
Dr. Dennis Hancock
Extension Forage Agronomist
4