Figure 1. Stocking Rate Calculation
Need to know 2 things: Annual production or total available forage Animal demand
Animal demand: Potential forage dry matter intake based solely on animal related factors such as body size, age and production stage.
Animal demand = 1,000-pound cow (1 AU) x 3 percent of body weight intake per day x 365 days = 10,950 pounds of forage per animal per year
Setting the initial stocking rate Example: 3,000 pounds per acre total available forage 3,000 pounds x 25 percent harvest effi ciency = 750 pounds per acre of allowable forage for grazing 10,950 pounds forage needed per AU/750 pounds allowable for grazing) = 14.6 acres per AU initial stocking rate
Don’t forget to compensate! Compensate for percentage of grazeable acres: 30 percent of range is “ungrazeable” due to dense brush, topography, roads, headquarters, etc. 14.6 acres per AU/(70 percent grazeable acres = 20.8 acres per animal unit corrected stocking rate
forage is produced by July 1 to July 15,” Goodwin ex- plains. “Expected forage production during a normal year is presented in the ecological site description. If a site is capable of producing 3,000 pounds of forage per acre by July 15 and I only measure 2000, something is wrong. Either the stocking rate is too high or there is a lack of rainfall. “These are the kind of contingency triggers we
consider when making stocking and drought manage- ment decisions.” Goodwin continues, “The second time I like to
measure production is after the fi rst killing frost in the fall. This measurement tells me how much forage was consumed during the growing season and how much is available for winter feed. “Only perennial forage is clipped and weighed for
determining stocking rates,” Goodwin says. “Most an- nual plants appear when there is adequate soil moisture and not during dry periods. Because of their moisture requirements, annuals cannot be relied upon for a continual supply of forage. Plants unpalatable to the ranch livestock are also discarded and not weighed. Ecological site descriptions list the preferred plants for various grazing animals.”
84 The Cattleman February 2014
Table 1. Forage mass at different average pasture heights as measured with a ruler.1
RULER HEIGHT (inches)
3.0 4.0 5.0 6.0 7.0 8.0 9.0
10.0 11.0 12.0 13.0 14.0 15.0 16.0 17.0 18.0
THIN 822
1064 1291 1502 1697 1876 2039 2178 2319 2435 2536 2620 2689 2742 2780 2801
FORAGE MASS AVERAGE
THICK
(dry matter pounds per acre) 1037 1338 1617 1874 2109 2321 2511 2679 2824 2948 3049 3128 3185 3219 3231 3221
1530 1987 2417 2821 3198 3549 3873 4170 4441 4686 4904 5096 5260 5399 5511 5596
1Adapted from “Estimating Pasture Forage Mass from Pasture
Height”; Ed Rayburn and John Lozier; West Virginia University Extension Service; October 2003.
Calculate stocking rates Goodwin states, “To determine stocking rates we
need to know 2 things — animal demand and forage supply. We also need to know how much of the total available forage we are going to allow livestock to graze. “Many of us have heard of the ‘take half-leave half’
rule. The problem with that rule of thumb is we as- sume we can graze half or 50 percent of the forage. That is not necessarily the case. We do need to leave 50 percent of the forage weight for the plant to remain vigorous and healthy; however, half of the remaining 50 percent is lost to insects, trampling, defecation and other means. “Only 25 percent of the standing forage is available
for grazing. Removing more than 50 percent over the course of the year can limit root development and, de- pending on timing, it can adversely affect next year’s growth potential,” Goodwin explains. Most stocking rates are based on an animal unit
(AU) which is a 1,000-pound mature cow and her calf up to 6 months of age, or 2 500-pound stocker animals. How many of us have 1,000-pound cows? If the herd is composed of 1,200-pound mother cows, each animal is 1.2 animal units. It’s easy to
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