Calculating Stocking Rate

March 10, 2015 Print Friendly and PDF

Written by Rachel Frost, Montana State University

The most important decision for successful range management is setting a proper stocking rate. Stocking rate is defined as the number of animals grazing on a given amount of land for a specified time. Stocking rates are often expressed in AUs/unit area.


4 Steps to Setting a Basic Stocking Rate:

1. How much forage do you have?
The first step toward determining how many animals the grazeable portion of a management unit can support is to measure how much forage the area produces. The amount of forage produced can vary greatly from year to year depending on weather; therefore, estimated forage production for determination of stocking rate should not be based on one year of forage production data. Managers can estimate the forage production of their land by mapping the management area into units of land that produce similar kinds and amounts of forage. These units are termed ecological sites or habitat types and most often will differ in soil type and plant productivity. Each unit should be surveyed to determine biomass production by 1) mowing or clipping small areas, 2) referring to picture guides to visually estimate amount of forage available, or 3) referring to site guides to estimate average productivity of the site. Only a certain portion of the biomass can be safely removed, and this depends on the vegetation and other management objectives. A common starting point is that 50% of the annual production that is potential forage can be harvested each year. Once a biomass estimate for each site has been obtained, multiply the number of acres within each site by its estimated biomass production per acre and sum these values for a total amount of potential forage produced. Finally, multiply the total amount of biomass by the percent of allowable use to obtain the total amount of forage available for livestock use.
2. How much of that forage can be used by grazing animals? (Usable Forage)
Land characteristics such as topography and distance from water influence the amount of forage available to grazing animals. Forage in areas with very rough or steep topography may be inaccessible to grazing animals or used much less than forage on level ground close to water. For example, grazeable plants located two miles or more from water are essentially unusable for livestock. They represent potential forage for livestock if the animals could be enticed to use the area. All management units should be stratified into areas of available and potential forage. Areas of potential forage identify management opportunities to improve livestock distribution across a greater portion of the landscape.
3. How much forage do your grazing animals need? (Forage Demand)
To calculate how much forage your grazing animals will need, you must determine the average weight of the animals in a herd or flock and the number of days the herd will graze the management unit. The average daily forage consumption of an animal — a combination of eating, trampling, and spoilage from urine or feces — will vary with the nutritive quality of the forage; however, an annual average of 2.6% is usually acceptable. For example, a 1,200-pound range cow that consumes 2.6% of her body weight requires 31 pounds of forage per day (1,200 pounds * 2.6%). When you multiply the animal's daily need by the number of days the management unit will be grazed, you obtain forage demand for that period. In the example above, if the cattle grazed the unit year round, then each cow would require 11,315 pounds (31 pounds * 365 days) of forage for the year.
4. What is your appropriate stocking rate?
Now that you have answered the above questions — how many animals can you graze and for how long — to determine the number of animals that can be grazed on a management unit, you must divide the pounds of usable forage by forage demand. For example, if a management unit that is grazed year long has 465,000 pounds of usable forage, and annual forage demand per animal is 11,315 pounds of forage, then 41 cows can graze the unit for 12 months. If the grazing period is less than 12 months, then more animals can graze the area for a shorter period. A three-month grazing period would have a stocking rate of about 164 cows [465,000 pounds of available forage /(31 pounds forage/head/day * 91 days) = 164.8 head].
 

Adapted fromLaunchbaugh, K.L. Forage Production and Carrying Capacity: Guidelines for Setting a Proper Stocking Rate

For additional help on calculating stocking rates, see the following resources: Pratt, M. and A. Rasmussen. 2001. Determining Your Stocking Rate. Utah State University Extension Publication NR/RM/04

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This work is supported by the USDA National Institute of Food and Agriculture, New Technologies for Ag Extension project.