Pasture measurement allows a grazier to determine how much forage dry matter is available in a pasture paddock, and once that is estimated, the producer can figure out how many animals should be grazed for a given period of time.

“Pasture measurement will help the grazier to make decisions about how to best use pasture paddocks and over time will provide a trend of how much forage dry matter is being produced per week,” said Rory Lewandowski, an Ohio State University Extension educator in agriculture and natural resources. “Using this type of information can help a grazier plan the livestock rotation for periods of rapid growth as well as periods of slow growth. The trend can provide an early warning system in a drought year and help the grazier plan accordingly.”

Lewandowski offers some strategies for taking pasture measurements. One strategy is to measure a paddock due to be grazed on a weekly basis.

“This will help to give you an idea about your rotation speed. If you are consistently measuring 2,400 to 3,000 pounds of forage dry matter per acre in paddocks about to be grazed, this indicates the rest period has been long enough,” said Lewandowski. “If forage dry matter is less than 2,200 pounds per acre, then rotation speed should be slowed down to allow the pasture more time to recover and grow.”

Another strategy is to measure the paddock before and after animals are turned out.

“These additional measurements will give you information about how you are managing plant residual, an important part of how quickly a plant recovers from a grazing pass. Most pastures should be managed so there is 1,200 to 1,400 pounds of forage dry matter after animals have grazed,” said Lewandowski. “The other advantage of this strategy is that you will get a good idea of pasture growth rate in terms of how much dry matter is being added per acre each week.”

To take pasture measurements, the most economical option is to use a pasture stick. The current pasture stick model being used in Ohio has a scale to measure forage height, a scale to estimate forage density, a table of pounds of dry matter per inch for various pasture forage types, information about length of grazing rotations, and information about calculating the pounds of dry matter available for grazing.

The basic steps involved in using the grazing stick are:

• Measure pasture height in 20 to 30 random areas of the paddock. Record those heights.
• Add the measurements to get a total and then divide that total by the number of measurements. This will give you average pasture height.
• Estimate pasture density using the dot scale on the pasture stick. This will allow you to estimate the pounds of dry matter per inch.
• Multiply the average height (in inches) by the pasture density (pounds of dry matter per inch). This will give you the total dry matter per acre in that paddock.
• Subtract the amount of residual dry matter you want to leave in the paddock. This is plant height after grazing times the pounds of dry matter per inch.

“If you plan for a 3- to 4-inch residual, 1,200 to 1,400 pounds is about right,” said Lewandowski. “Consider the result of total dry matter minus residual dry matter to be the forage available for grazing.”

• Figure out the amount of utilizable forage.
“All of the forage available for grazing will not actually get grazed. There will be waste,” said Lewandowski. “The smaller the paddock size and the fewer days animals spend in that paddock, the higher the grazing efficiency.” If you are moving animals every 3 to 4 days, use a 60 percent grazing efficiency to start with, said Lewandowski. Multiply the available forage dry matter by the grazing efficiency expressed as a decimal. For example, 1,500 pounds of dry matter times 0.60 equals 900 pounds of utilizable forage dry matter per acre.

• Figure out the livestock need in pounds of dry matter per day.
“Most livestock will consume between 2.5 to 3.0 percent of their bodyweight in dry matter per day,” said Lewandowski. “You will need to know the average bodyweights of your livestock.” Multiply the dry matter per day requirement for an individual animal by the total number of animals that will graze in that paddock.

For example: 30 head of sheep that average 150 pounds, consuming 2.75 percent of bodyweight in dry matter per day is 150 times 0.0275 equals 4.1 pounds of dry matter per day. And 4.1 times 30 head equals 123 pounds of dry matter per day that is needed.

• Figure out what the paddock can support. Divide the utilizable forage by the livestock requirement to get how many days of grazing the paddock will provide. For example: 900 pounds of utilizable dry matter divided by 123 pounds of dry matter needed per day equals 7.3. “There should be about a week’s worth of grazing in this paddock,” said Lewandowski.

• Make adjustments based on the measurement calculations. “For example, if your goal is to rotate every three to four days, and in our example we found that one acre is providing seven days’ worth of grazing for 30 head of sheep, then provide about 0.5 acres every three days,” said Lewandowski.

Another option to measure pastures is the rising plate meter, which has a built-in counter. To use the rising plate meter, record the beginning number on the counter, make 30 measurements, and record the end number. Then subtract the end number from the beginning number and divide that result by the number of measurements to get an average. Multiply this average by a conversion factor (currently 107.04) for cool season grass pastures. Use this number as the total forage dry matter acre and follow the steps outlined for the pasture stick to make the remaining animal use calculations.

“The plate meter is quicker, but the cost of this instrument is about $450, compared to $5 to $7 for the pasture stick,” said Lewandowski. “It is important for graziers to put some effort into pasture measurement if they want to increase their pasture management skills. Pasture measurement can help to take some of the guesswork out of allocating pasture forage and it can help to reduce the slope of the learning curve associated with management intensive grazing.”  FG

—Excerpts from Ohio State University news release

Candace Pollock
Associate Editor
CommTech News
Ohio State University