7. Determine stock unit days of grazing available. A stock unit is based on the metabolizable energy requirements (17.3 mega calories per day) for a 1,000 pound cow in the last third of pregnancy (Troxel and White, 1988). This requirement converts to a daily forage intake of 19.6 lb. of 53.6 percent digestible forage. To calculate the stock unit days of grazing available, first multiply the total pounds of forage supply per pasture by 0.25. (The quantity of forage that can be eaten by livestock under proper management is approximately 25 percent of the total forage supply). Divide this number by the pounds of forage required per day (19.6 lb.) per stock unit to determine the number of stock unit days of grazing available. The number of stock unit days of grazing available per pasture can be used to determine if the forage supply is adequate for the planned stocking rate until regrowth is expected. Determine the average number of stock units that you plan to graze during this period of time. Divide the planned number of stock units into the stock unit days of grazing available. This estimates the number of days this forage supply will last at this stocking rate. Example Forage Survey Application and interpretation of a forage survey can best be understood by using an example pasture. The pasture is 1,014 acres in size. Roads and gas pads and nongrazable brush motts occupy approximately 5 percent of the Low Stony Hill and Shallow Divide range sites. Three range sites occur in the pasture (Table 2). Table 2. Grazable acres in Dago pasture Range Site Total Area (acres) Nongrazable Area (acres) Grazable Area (acres) Clay Loam 72 2 70 Low Stony Hill 666 33 633 Shallow Divide 276 14 262 Total 1,014 49 965 A forage survey was conducted for each range site in July 1989. Details for the shallow divide site are shown in Figure 2. Results of the survey indicated the following amounts of forage by range site in the pasture (Table 3). Table 3. Amounts of forage by range site Range Site Grazable Area (acres) Average Forage Supply (lb/ac) Total Forage Supply (lb) Clay Loam 70 1,372 96,040 Low Stony Hill 633 601 380,433 Shallow Divide 262 1,137* 297,894 Total 774,367 * See Figure 2 for method of calculation. [Next Page] Authors: Larry D. White, Calvin Richardson