Assessing pasture forage is a key step in planning grazing strategies. Although most producers understand the importance of assessing production, few invest the time necessary to clip and weigh vegetation within and across seasons to build a long-term database for their pastures. Recognizing this inherent need, range managers have developed simplified tools that allow rapid estimation of forage production and availability in pastures without the need to continuously clip and weigh vegetation. One of these tools is the common ‘grazing stick.’
While all grazing sticks are based on the same general principals, their use can be modified to fit local conditions. Here, we introduce the grazing stick developed for the South Dakota Grassland Coalition by the South Dakota U.S. Department of Agriculture Natural Resources Conservation Service (USDA NRCS). This stick is distributed at multiple grazing management events throughout South Dakota. While small modifications have been made over the years, any version of the South Dakota grazing stick will adequately serve to help estimate your pasture conditions.
How Does the Grazing Stick Work?
The grazing stick utilizes simple plant leaf height measurements in inches. For every inch of growth, the grazing stick estimates how many pounds of dry plant material are available. This number is then represented as pounds per-acre, per-inch of growth. So, 10 inches of growth at 100 pounds per-inch equates to 1,000 pounds per-acre of dry plant material. The grazing stick includes simple math to determine herd size, stocking rates and available grazing days. We will address how to use the grazing stick in steps.
Step 1: Timing
When to assess pasture forage is a common question. In South Dakota, the growth and development of our pastures is largely dependent on the dominant plant community, such as: 1) native cool-season grasses (native wheatgrasses, needlegrasses), 2) non-native or invasive cool-season grasses (Kentucky bluegrass, bromegrasses, exotic wheatgrasses), 3) native warm-season midgrasses (blue grama, buffalograss), 4) native warm-season tallgrasses (big bluestem, indiangrass, sideoats grama) or 5) a mixture of grasses and forbs from several of these categories. To assess total production for pastures dominated by cool-season vegetation, late-June to early-July approach peak production. For a warm-season dominated pasture, mid-to-late August works well. However, pasture production can be assessed at any time to determine stocking rates or grazing days within a rotational grazing system and should be measured prior to moving livestock to the next pasture in the rotation.
Step 2: How and Where to Measure
The grazing stick is designed to measure the average leaf height of the vegetation in the pasture by providing a simple yardstick-style ruler on one side.
The first part of the stick to notice is the DO NOT GRAZE indicator that reminds a producer not to remove the vegetation beyond a height of four inches. Generally, one-half of a plant’s above ground biomass is located in the bottom one-third of the plant. Removal of over 50% of a plant’s biomass can severely impact root development, requiring long-term rest for the plant to recover. The four-inch mark is provided as a safety measure for producers and should not be ignored (Figure 1).
For the grazing stick to accurately determine overall forage availability, leaf height must be measured in an upright position.
Trampled vegetation may need to be held upright in one hand in order to determine the average leaf height of the grass, not total plant height. Therefore, stems and seed heads of tall grasses should not be used when measuring average leaf height (Figure 2).
A good rule of thumb is that grazing stick measurements should be taken at no less than 15-to-20 locations within a pasture. Areas where measures are taken should be a fair representation of the overall pasture vegetation. Distribution of various types of vegetation should be considered as well. For instance, in a 100-acre pasture that is dominated by warm-season grasses on the west side and cool-season grasses on the east side, a good strategy may be to take 15 measurements on each side and work through the grazing stick methodology, averaging the final production numbers together.
For a pasture with equal distribution of a variety of vegetation, one must decide which vegetation category of the grazing stick most closely fits the situation. Vegetation categories are found in the ‘Estimated Air-dry Weight’ table on the stick (Figure 3, Table 1). This table includes information on the plant community. The user must choose which plant community and stand density most closely represents the pasture conditions (Figure 3). To determine stand density, one must look ‘into’ the stand to determine relative density. This is where the grazing stick table in Figure 3 and Table 1 assists the producer. Notice the notes on the bottom of Table 1 indicating stand density should be greater than 85% to qualify as excellent.
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| Cool-Season and Legume |
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| Cool-Season Introduced |
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| Cool-Season Native |
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| Native Mixed Cool and Warm |
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| Warm-Season Native |
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* Measure the average height in inches of the vegetative forage in the plant community, not seed head height.
** Stand density refers to the relative closeness of desirable plants.
An excellent stand density will have a cover greater than 85% and be vigorous.
Vegetation cover can be somewhat subjective. The grazing stick table allows for a great deal of flexibility in determining the range of pounds per-inch of production within the stand density table (Figure 3, Table 1). It is up to the producer to decide how many pounds per-inch are likely being produced within the chosen stand density category. Also, within a given plant community in a single pasture, the stand density can be variable depending on the landscape, slope, soils and other conditions.
The producer should evaluate the pounds per-inch at every measurement if there is a high variability in stand density. The best way to accurately determine pounds per-acre is to calibrate your grazing stick estimates via a true forage clipping estimation.
As an example, Figure 4 and Figure 5 are provided to help the user understand the nuances of stand density estimation. Figure 4 depicts a mid-July pasture dominated by smooth bromegrass, which is a ‘cool-season introduced’ plant community in the grazing stick table. This stand would likely be categorized in the ‘Normal’ range, producing an estimated 100 pounds per-inch based on its fairly low density and relatively short (20 inches) stand height.
Figure 5 depicts a mid-July pasture dominated by big bluestem, which is a ‘warm-season native’ plant community in the grazing stick table. This stand would likely be categorized in the ‘Excellent’ range, producing an estimated 300 pounds per-inch based on its high density and relatively tall (34 inches) stand height.
Step 3: Estimating Average Pounds Per-Acre Production
Once several height measurements have been taken and a general stand density estimate has been determined by averaging samples across the pasture, simply multiplying the average height from the measurements by the average pounds per-inch will yield the average pounds per-acre value for the pasture. An average of 20 inches of growth with an estimated 100 pounds per-inch in our smooth bromegrass stand in Figure 4 would yield about 2,000 pounds per-acre. At 34 inches of growth with an estimated 300 pounds per-inch, our big bluestem stand in Figure 5 would yield over 10,000 pounds per-acre. It is important to understand that at this point that we’ve only estimated our potential yield. This number does not equate our forage supply (available forage).
Step 4: Determining Forage Supply (Grazing Efficiency) and Forage Demand
Forage supply is an estimate of how much available forage is in the pasture. It is determined by multiplying the forage production by the percent of the forage the manager is willing to remove through grazing. The basic rule-of-thumb is the standard ‘take one-half, leave one-half’ approach. The basics of this approach call for 50% of the forage to remain in the pasture as ungrazed, while 25% is consumed by livestock and 25% assigned to disturbance through trampling, defecation and consumption by other grazers, such as insects and small mammals. In this scenario, our smooth bromegrass pasture would have a forage supply of 500 pounds available to be grazed (25% of 2,000 pounds) while our big bluestem pasture would offer over 2,500 pounds of available forage. As one increases the number of pastures in a grazing rotation, the allowances for grazing efficiency also increase. Figure 6 and Table 2 highlight the grazing rotation chart offered on the grazing stick to help producers determine the forage supply (grazing efficiency) of their pastures.
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Forage demand is determined by the type and size of livestock and the conditions under which they are grazed. The simple chart provided on the grazing stick can help the producer determine an estimate of daily or monthly forage intake of the herd.
For general purposes, a standard measure for a lactating beef cow is about 3% of body weight, or 30 pounds of dry matter per-day for a 1,000-pound cow. Heavier cows will consume more total pounds at the same 3% intake rate. The grazing stick again offers a simple chart to assist producers in these estimates (Figure 7, Table 3).
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| Sheep |
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| Sheep |
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| Yearling |
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| Yearling |
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| Cow |
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| Cow |
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| Cow |
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| Cow |
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Step 5: Calculating Grazing Days, Herd Size or Acreage Needed.
Once the forage supply and the daily forage demand have been calculated, one can use the numbers to determine: 1) the size of pasture needed to graze a certain number of animals, 2) the number of animals a given pasture can carry during a pre-determined timeframe or 3) the number of available grazing days a herd may have in a particular pasture. These simple calculations are provided on the grazing stick as illustrated in Figure 8 and Figure 9.
Calculations Used
Forage Supply
Pounds/acre (air-dry) × % Grazing Efficiency = Pounds/acre forage available
(% Grazing Efficiency = 25% - 1 pasture; 35% - 4–8 pastures; 40% - 12+ pasture MIG)
Forage Demand
Animal Weight × 3.0% of Body Weight = Pounds forage required/day
(Or use Average Forage Intake in Table 3)
Pasture Size (Ac.)
[(Forage Demand: lbs./day × # of Animals) ÷
Forage supply: lbs./acre] × Grazing Period in Days
Animal Number
(Forage Supply: lbs./acre × Pasture Size in Acres) ÷
(Forage Demand: lbs./day × Grazing Period in days)
Grazing Period (Days)
(Forage Supply: lbs./acre × Pasture Size in Acres) ÷
(Forage Demand: lbs./day × # of Animals)
Example Scenarios
Scenario One - Calculating Pasture Size (Figure 8): In some cases, there may be a need to graze a fixed number of animals for a fixed period of time, and the producer must determine how many acres are necessary. Step one is to determine forage demand. If we have 1,500-pound cows, we can determine the daily forage demand per-cow (1,500 pounds × 3% = 45 pounds of dry matter per-cow, per-day). A single cow will need 6,750 pounds of dry matter forage for a 150-day grazing period (45 pounds per-day × 150 days). A herd of 100 such cows will need 675,000 pounds of forage for the season. If these cows are to graze on only one pasture for the season, we would then assign a grazing efficiency of 25%. To determine the total forage production necessary to sustain the herd, we can now divide 675,000 pounds by .25, which equates to 2,700,000 pounds of forage production necessary. To figure out our acres needed, we then divide the 2,700,000 total pounds needed by 2,000 pounds per-acre production in our brome pasture, yielding an answer of 1,350 acres necessary to sustain this herd for the 150-day season.
Scenario Two - Calculating Herd Size: If we know we have a certain amount of forage available and we want to ensure grazing for a certain number of days, we can also calculate our animal number using the grazing stick. If we use our single 100-acre brome pasture at 2,000 pounds per-acre production and 25% harvest efficiency, we will have 50,000 pounds of available forage. If we want to utilize that pasture for 150 days and we have our same 1,500-pound cows, we know from Scenario One that each cow will need 6,750 pounds of forage to sustain her through the season. To determine the number of cows we can graze, we simply divide the available forage (50,000 pounds) by the pounds per-head for the season (6,750 pounds). Therefore, we can graze about 7.4 cows on this pasture for the season.
Scenario Three - Calculating Grazing Days: If we have a similar herd of 20 1,500-pound beef cows, we know they need 900 pounds of forage per-day (20 cows × 45 pounds per-day, per-cow). We know from Scenario Two that our forage supply is 50,000 pounds. At 50,000 pounds available forage supply, our pasture can handle our herd of 20 cows for about 55 days (50,000 pounds ÷ 900 pounds per-day).
Of course, it is always necessary to account for forage quality and timing of grazing, but if used properly, the grazing stick can help a producer become more familiar with his or her pastures, gaining valuable insight over time in order to assess grazing potential and the nuances that might impact the pastures and the ranch as a whole.
