Estimating and measuring pasture productivity

Estimating or measuring pasture productivity is useful for management purposes.

One unit of measure often used is animal unit month (AUM), the amount of forage required by one animal unit (AU) for one month. An AUM is based on an animal intake of 2.5% to 3% of body weight per day on a dry matter basis, that is adjusting for moisture content of feed. Intake can change with differing nutrient content of feed or nutrient requirement of animals.

Here is an example:

• A 1,000-pound cow eating 2.5% of its body weight eats about 25 pounds per day (1,000 pounds x 0.025)
• This is equal to 750 pounds of forage for one month (25 pounds/day x 30 days/month)
• One AUM is feed for one AU for one month during the growing season
• Five AUM is feed for one AU for five months (or five AU for one month) during the growing season

Estimating and measuring forage production can be done by various other methods such as clip and weigh, plate meters, pasture sticks, and more. See Chapter 16 of the Pasture and Grazing Management in the Northwest (PNW 614).

Estimating productivity

The NRCS Web Soil Survey has data for different soil types in the United States. Potential productivity in AUM per acre or tons of hay per acre for different crops are listed for defined areas of interest (property or management units of a farm).

Measuring productivity

You can measure productivity on your pastures by tracking the number, type, and weight of the animals you graze over time. Add up all the AUM and compare that to the potential productivity using the NRCS data as described above. If there is room for improvement, consider changing some of your pasture management practices.

Animal unit equivalents

One AU is equivalent to a 1,000-pound cow. But this can be converted to different sizes and types of animals (Table 1).