Carrying Capacity Calculator

Method 1

Carrying capacity, also known as grazing capacity, is the amount of forage available for grazing animals in a specific pasture or field. Understanding how much forage is available is a key principle of pasture management in order to balance the available forage supply with livestock demand.

Carrying capacity can be calculated using a variety of techniques and is somewhat based on trial and error. Carrying capacity can be monitored and adjusted over time to determine the long-term average.

The BCRC Carrying Capacity Calculator allows producers to determine the carrying capacity of pastures based on two methods: 1) estimates based on provincial guides and 2) field-based sampling.

Producers can use the Method 1 calculator if they wish to calculate an estimate of carrying capacity based on available provincial forage production guides. Using Method 1 is easy and works best when the pasture condition (or range health) is similar throughout the field and the forage plant community (or range type) is uniform.

Producers can use Method 2 if they plan on clipping, drying, and weighing samples collected from their pasture. Field-based sampling provides greater accuracy but requires more hands-on work. Producers may choose field-based sampling if provincial guides are unavailable for their region or if pasture types or conditions vary within their field. Forage production varies each year, so the Method 2 approach should include multiple years of sampling to estimate the long-term productivity of the pasture.

Method #1: Use Provincial Production Guides

Step 1: Determine Pasture Condition using Table 1 or using the Pasture Scorecard on page 39 of the West Central Forage Pasture Planner

Table 1. Tame pasture condition class definitions
Category Excellent Good Fair Poor
Potential yield of the area 75-100% 60-75% 50-60% 33-50%
Production from desirable, adapted grass and legumes 95% 90% 60% Less than 50%
Production from weeds or undesirable plants Less than 5% Less than 10% 20% or more 50% or more
Fertility Program Average to above average Average Below average or non-existent No fertility program
Source: Alberta Forage Manual (Table 37, page 206) adapted from Wroe et al. (1988) Guide to Range Condition and Stocking Rates for Alberta Grasslands

Step 2: Determine Estimated Forage Yield using Table 2

Table 2. Estimated forage production based on tame pasture condition (Animal Unit Months per acre or pounds per acre)
 
Pasture Condition
Precipitation Zone
Excellent
Good
Fair
Poor
mm / inches AUM/ac LB/ac AUM/ac LB/ac AUM/ac LB/ac AUM/ac LB/ac
250-350 / 10-14 0.75 700 0.5 460 0.4 370 0.25 230
350-450 / 14-18 1.25 1,150 0.8 740 0.6 550 0.4 370
450-550 / 18-22 2 1,850 1.4 1,300 1.1 1,000 0.7 650
550-650 / 22-26 3.3 3,000 2.2 2,000 1.6 1,500 1.1 1,000
Irrigation 7.5 6,900 5 5,150 3.75 3,500 2.5 2,300
Source: Alberta Agriculture Beef Cow-Calf Manure or Alberta Forage Manual (page 205) adapted from Wroe et al. (1988) Guide to Range Condition and Stocking Rates for Alberta Grasslands

Click here to find additional provincial and regional forage estimates and assessment tools.

Step 3: Calculate Available Forage

Use the table above to determine forage supply.

The utilization rate determines how much forage is used or lost to grazing, trampling, insects and wildlife. This helps determine how much forage material should be left behind to maintain future production. Utilizing pasture at a rate that exceeds the plant communities’ ability to recover can lead to lower forage production and encourage less palatable/productive forage plants to invade the pasture, including weeds. Choose a realistic utilization rate that will ensure adequate pasture recovery following grazing.

Recommended utilization rates for native pastures vary from 25-50%. For tame pastures, recommended utilization rates range from 50-75% depending on fertility. If the pasture is forested or brushed, adjust acres to reflect available grazing rather than the total acres in the field. Alternatively, the utilization rate for forested or brushy pasture can be reduced to 25% using the entire pasture size.

Enter pasture information in yellow cells.

Forage Supply (lbs/acre)
Utilization Rate %
Available Forage for Grazing (lbs/acre)
370
Pasture Size (# of acres)
Total Forage Available in Pasture (lbs)
59,200
Total Animal Unit Months (AUMs) of Forage Available
75.9
Total Animal Unit Days
2,277

Step 4: Calculate the number of pairs or yearlings that can graze

Different classes, or sizes, of cattle consume different amounts of forage, with bigger animals eating more available forage. Use the chart below to find an Animal Unit Equivalent (AUE) similar to your grazing animals and enter in the yellow cells.

Cow-calf Pair Yearling  
Animal Unit Equivalent
58.4
89.3
 Number of pairs/yearlings that can graze for one month
1,751
2,679
 Total pairs/yearling grazing days available

Animal Unit Equivalent Chart
Animal Type Animal Unit Equivalent
Cow, dry (1000 lbs) 1.0
Cow, 1300 lbs with calf to 4 months 1.3
Cow, 1400 lbs with calf to 4 months 1.4
Cow, 1500 lbs with calf to 4 months 1.5
Yearling Steer 0.85
Heifers, 700 lbs 0.80
Bulls, mature (1700 lbs. average) 1.7

Additional Regional Information

Table 3. Average stocking rate for ecosite in each ecoregion
Ecoregion Climatic Moisture Index (mm) * AUM/ac
Dry Mixed Grassland below -325 mm 0.2
Mixed Grassland -325 to -225 mm 0.29
Aspen Parkland, drier portion -225 to -125 mm 0.44
Aspen Parkland, moister portion above -125 mm 0.68
Source: Saskatchewan Rangeland Ecosystems Table 11

* Climatic Moisture Index is the amount of annual precipitation minus the annual potential evapotranspiration for an ecoregion.

Click here to download the Excel Version of this Calculator