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The ability to accurately estimate forage dry matter availability and animal forage dry matter demand is critical in balancing forage plant persistence and animal performance. A grazing stick is a tool that a grazing manager can use to estimate available standing dry matter. As with any tool, taking time to learn how to properly use it will increase the accuracy of the results.
A very basic first step is to understand that forage yields and animal forage demand are expressed in terms of dry matter or "dry matter basis." This simplifies calculations as moisture content of forage will vary according to season, growth stage and species. For example, a 1,100 lb dry cow has a dry matter requirement of approximately 30 lbs/day. If she is grazing a pasture that has a moisture content of 60%, to meet her dry matter demand of 30 lbs, she will consume a total volume of 50 lbs of forage. When moisture is included, this is termed "as-fed" or "as received." Step 1
A more complete table is found on your grazing stick. When measuring canopy height, take several measurements across the area to insure that canopy height is representative of the entire pasture. Measure to the top of the canopy. If the canopy has fallen over, straighten, but don’t stretch, the canopy to measure (Figure 1).
Example: A bermudagrass canopy height of 10" and an average good value of 235 lbs/ac in would equal a dry matter availability of 2350 lbs/ac. To reduce the variation in the range of lbs/ac and calibrate both your eye and the grazing stick, clip random, representative forage samples using a frame measuring 12" x 23". Measure canopy height where forage is clipped. Weigh and record sample weights in grams. Save a sub-sample to determine forage moisture content (see formula on back). Use the following formulas to determine lbs/ac with a 12" x 23" frame: You may continue to calibrate your eye and the grazing stick throughout the
growing season or until you become comfortable estimating % dry matter and stand
density. At that point, simply measure canopy height and convert lbs/ac in to
lbs/ac. Step 2
Percent utilization will vary according to plant species, season and management
goals. Introduced forages will generally have higher utilization rates than
native forages. The rule of thumb is 65 to 70% for bermudagrass and 25 to 30%
for native grass. Step 3 This is determined by estimating what percent of an animal’s body weight it will consume in dry matter in one day. The percentage will vary according to class of animal and forage quality (Table 2). An approximate range is 2 to 4%. A value of 2.5% is most often used. • 1,100 lb cow X 2.5% intake = 28 lbs of dry matter demand per head per day
Step 4 Grazing stick estimate of bermudagrass yield = 2,360 lbs/ac Your grazing stick has helped you determine reserve herd days. In this example, one acre of bermudagrass will supply grazing for one cow for 54 days.
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© 1997-2008 by The Samuel Roberts Noble Foundation, Inc.
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