A rule of thumb is 1 inch of pasture contains about 300 pounds of dry matter per acre. Experienced graziers estimate pasture mass by eye, by using a rising plate meter, or with a measuring stick. A stick ruler can be useful in estimating dry matter in a pasture. Place the yardstick lightly on the ground and measure to the average height of the sward or leaf area. For cool-season perennial pastures, multiply the height by 300, and you have the total dry matter in the field. Reduce that estimate by 900 pounds because you want to leave 3 to 4 inches of growth behind to help fuel the new growth. This is only a guideline, however, because different pasture species and mixtures have different pasture densities, and the most desirable height of the pasture after grazing also varies by species.
A “rising plate” or “floating plate” meter provides a measurement similar to that described with the yardstick, and these have the advantage that they account for the density of the sward. These plate meters may incorporate electronics which use conductivity to measure the thickness of the sward. Here again, these need to be calibrated to the type of sward.
There is no foolproof measure, and pasture management is as much an art as a science. Monitor the height and condition of the residual pasture after grazing as one check of animal consumption. Check the body condition of the cattle periodically as one measure of animal performance. For milking cows, milk production should be monitored closely to ensure pasture intake is supporting the desired level.