Carrying Capacity Calculator

Instructions:
Use the field sampling method to estimate forage yield.
Enter your own pasture and herd information to estimate carrying capacity.

Step 1: Measure Pasture Yield

Field-based sampling provides greater accuracy but requires more hands-on work.

Required materials: a 50 cm x 50 cm square frame (1/4m²), scissors for cutting grass, paper bags, markers to identify each sample, method for drying forage and a scale.

Step 1a: Taking Samples
Take enough samples to capture the variation in the pasture (e.g. low spots with high productivity and high spots with low productivity) to be representative of production across the entire field. The number of samples taken will vary with the size of the field and uniformity of the field.

Keep each sample separate and contained in its own bag.

1. Place the square frame in the grass. Ensure only grass with roots inside the frame is included.
2. Hand rake litter (dead forage from previous years) out of the frame and discard.
3. Clip the forage to a height of 2.5 cm or 1 inch and place into the bag.

For more information on collecting samples from standing forage, visit the BCRC Feed Testing page.

Step 1b: Dry, Sort, Weigh and Record
Grass clippings can be dried in a food dehydrator or at room temperature over several days. It is not recommended to use a microwave.
Weigh each sample separately using a kitchen scale. Enter all weights as grams.

1. Weigh the total forage in the bag and enter into the first row below
2. Sort the litter from the green material. Tweezers make this job easier
3. Weigh the green material and enter into the second row below
4. Litter weight is calculated and does not need to be separately weighed

Note the percentage of litter cover. The amount of litter left on the land can make a big difference in the performance of the pasture. Litter includes ungrazed residue from the previous year’s growth, residue from bale grazing, fallen stems, leaf material and other partially decomposed material. Litter helps to conserve moisture by reducing evaporation, improving infiltration and cooling the soil surface.

Table 1. Forage yield from field sampling (dry matter basis)

Step 2: Calculate Available Forage

Enter Pasture Information in yellow cells.

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

Recommended utilization rates for native pasture 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.

Step 3: Determine Animal Unit Equivalents (AUE)

Different classes or sizes of cattle consume different amounts of forage. Either:

1) Use Table 3a below to find an Animal Unit Equivalent (AUE) similar to your grazing animals, or
2) Enter the average weight of your grazing animals into the AUE calculator (Table 3b).

Enter the AUE into the yellow cells in Step 4.

Step 4: Available Grazing Days

Enter the AUE determined in step 3 into the yellow cells below.