Dr. McCollum is an animal nutritionist with Texas A&M AgriLife Extension Service.
In the April article, we showed how McCollum determines stock flow and their animal unit month (AUM) grazing requirements. The next step is to design a forage production calendar.
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An example of estimated annual forage availability on the operation in its current state is shown in Table 1.
Forage production estimates can be obtained from university publications, state range/pasture extension specialists or the Resources Conservation Service (NRCS). Better estimates can be obtained by actually measuring forage production from representative areas in each pasture.
“The most accurate way of measuring the current amount of standing forage is clipping inside plot frames,” says Jason Hohlt, Zone 4 Rangeland Management Specialist, USDA-NRCS in Bryan, Texas.
“A plot-clipping frame can be made from quarter-inch PVC pipe. A recommended size of 12 inches by 23 inches provides a 1.92-square-foot area. Choose an area very representative of the pasture to clip. Everything rooted in the frame is clipped to ground level at enough locations to provide confidence that a representative sampling has been obtained."
"Weigh each sample using a gram scale and average the weights if more than one sample was collected. Next, determine percent moisture of the sample either by estimation or drying.”
Rocky Lemus, extension forage specialist at Mississippi State University, recommends drying forage in a microwave oven and determining amount of dry matter using the following procedure:
1. Weigh approximately 50 to 100 grams of clipped forage onto a microwave-safe dish or container. Heat the sample for two minutes at full power and then re-weigh it.
2. If forage does not feel completely dry, reheat it for 30 seconds. Re-weigh it. Continue drying and weighing until back-to-back weights are constant. Do not heat the forage to a point where it chars. If charring occurs, use the previous weight.
3. Calculate the average dry weight of all collected samples and convert to pounds per acre by multiplying the number of grams by 50.
4. To calculate moisture percentage, subtract the last dry weight from the original wet weight and divide this number by the wet weight. Now multiply by 100. This is the moisture content of the sample.
Once the estimated production of each type of forage is entered in Column 1 of Table 1, estimated harvest efficiency (expressed in percent) is entered in Column 2. Harvest efficiency is the proportion of annual forage production allocated to cattle grazing and is never 100 percent.
Maintaining health of a plant community requires that residues be left for ground cover. In addition, some plants or portions of a plant are unpalatable and are not grazed.
A percentage of forage production is lost to trampling, defecation, urination, insect feeding, wildlife habitat and weathering. Seek guidance from an extension specialist or NRCS on proper harvest efficiencies. Available forage in Column 3 is calculated by multiplying percent harvest by total production.
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Methods of calculating animal units were demonstrated in the April article with the results shown in Table 2 in both articles.
An animal unit (AU) is normally defined as one mature cow weighing about 1,000 pounds and her suckling calf, or an animal with a monthly requirement of 780 pounds of air-dried forage.
AU equivalents in Table 2 were derived by dividing the animal’s weight by 1,000. Animal unit equivalents are the units used to calculate forage demand and production.
Animal unit months per acre in Table 1 are derived by dividing 780 pounds into pounds per acre of available forage. Divide AUM per acre into “one” to obtain acres per AUM. Yearly consumption is 9,360 pounds, so calculate acres per animal unit year (AUY) by dividing available forage into 9,360.
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Percentages of the available forage supply grazed in certain months are listed in Table 3.
Knowing when to graze different types of forage and for how long comes from experience and from observing pastures frequently to gauge forage production. It is important to not overgraze plants.
Total available grazing in Table 3 is calculated by multiplying the percentage used by the available pounds of forage available as listed in Table 1 and then multiplying by the available acres of that particular forage. AUMs are derived by dividing total consumption by 780 pounds.
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Forage demand and available grazing through the year are compared in Table 4 to evaluate supply and demand compatibility and gaps in forage production.
These comparisons and evaluations show the need to stockpile forage and when additional forage supply is needed during the year. Stock demand and available forage appear fairly well balanced if you look only at the annual totals.
Examination of AUMs for each month, however, shows that stock demand for forage from June to October is much higher than the available supply, and from November to May, there is a surplus of available grazing.
Remedial action must be taken to avoid possible forced herd liquidation during the summer months. Solutions may be to reallocate land use by converting some of the acreage producing winter small grains into warm-season perennial grasses or summer annual crops that will provide forage in the summer and fall.
Beyond the above examples presented by McCollum, producers need to investigate ways to more efficiently utilize their current forage resources. Cross-fencing to improve grazing distribution and allow for rotational grazing may increase harvest efficiency.
Improved water systems may be another way to obtain better grazing distribution. Renovating introduced pastures and brush suppression on native rangeland may boost forage production.
Projecting forage requirements and developing a forage management plan to determine amount of available grazing should be completed before rebuilding the herd and making costly mistakes. 
Robert Fears is a freelance writer based in Texas.
