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Setting
Stocking Rates for Pastures
Cathie Erichsen Arychuk,
Bison Production Specialist, Alberta Agriculture
Reprinted from The Tracker; volume 4, issue 6, June 2000,
pages 72-73
Pasture forage production depends on soil conditions and climate.
Pasture production also depends on stand condition and plant species
present. Average stocking rates are a good starting point, but you
should determine a stocking rate for each pasture since pastures can
vary greatly.
Stocking rates are expressed as the number of Animal Unit Months
(AUM) supplied by one acre of pasture for one
year. An animal unit (AU) is defined as one mature 1000 lb.
cow with or without a calf. The animal unit is based on an
average daily forage consumption of 26 lbs. of dry matter (forage
dried until no moisture remains). Since the original animal unit
concept was based on beef cattle, we use animal unit equivalents to
deal with other animal sizes and species.
| Animal
Unit Equivalents |
AU |
| Bison,
mature cow - with or without calf |
1.0 |
| Bison,
mature bull |
1.5 |
| Bison, two
year old heifer |
0.7 |
| Bison,
yearling |
0.5 |
| Elk,
mature cow - with or without calf |
0.5 |
| Elk,
mature bull |
0.7 |
| Elk,
yearling |
0.3 |
The next table gives recommended stocking rates in AUMs/acre for
seeded tame pastures, in four condition classes, based on annual
precipitation. This table assumes average pasture inputs and a
continuous grazing system. When determining stocking rates for
pastures with effective rotational grazing systems and improved
fertility in zones with over 14 inches of annual precipitation, use
the stocking rates from the next higher precipitation zone. These
stocking rates are based on average conditions, and can be used as a
starting point in determining stocking rates. Over time you can
adjust the stocking rates for each of your pastures.
| Stocking
Rates for seeded tame pastures in Alberta (in AUMs/acre) |
| Annual
Precipitation Zones |
Pasture
Condition Class |
| mm. |
in. |
Excellent |
Good |
Fair |
Poor |
| 250-350 |
10-14 |
0.75 |
0.50 |
0.40 |
0.25 |
| 350-450 |
14-18 |
1.25 |
0.80 |
0.60 |
0.40 |
| 450-550 |
18-22 |
2.00 |
1.40 |
1.10 |
0.70 |
| 550-650 |
22-26 |
3.30 |
2.20 |
1.60 |
1.10 |
| Irrigation |
|
7.50 |
5.00 |
3.75 |
2.50 |
A pasture in excellent condition should produce 75 to 100% of the
top yield for the area, with less than 5% of
the total production coming from weeds or undesirable species. At least 95% of forage production should come from
adapted grasses and legumes. A pasture in good condition will
produce 60 to 75% of the top area yield, with 90% of this production
from adapted species. A pasture in fair condition will only produce
50 to 60% of the top yields for the area, with 60% of production
coming from adapted forage species. A poor condition pasture will
produce less than 50% of the area's top yield, and have less than
50% of the production from adapted species.
Example 1: Calculating the number of pasture acres needed for
your herd
Assume:
-18 to 22 inch annual precipitation zone
-Excellent pasture condition class (2.00 AUM/acre)
-Grazing season 165 days (5.5 months)
-80 bison cow/calf pairs (80 AU)
Required pasture
= AU x Months Grazing/AUM/acre
= 80 x 5.5/2.0
= 220 acres for the season
Example 2: Calculating Pasture Capacity
Assume:
-Annual precipitation zone 18-22 inches
-200 acre grass-legume pasture (excellent condition = 2.00 AUM/acre)
-Want 120 days of grazing (4 months)
Pasture Capacity
= Acres x AUM/acre ) months grazing
= 200 x 2.00/4
= 100AU
100 AU equivalents are 100 bison cow/calf pairs or 200 elk cow/calf
pairs. |
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