A critical part of a ranch situation analysis is current grazing capacity because it is the basic resource which determines ranch quality and profit potential. Animal nutritionists estimate quantity and quality of standing forage available through the year and then calculate needed supplement and minerals. The more standing forage that is available, the less money needed to buy feed.
Experienced range managers and forage specialists can walk across a pasture and accurately estimate the amount of forage just as cattlemen determine body condition by looking at an animal. Those of us who don’t have experience in determining grazing need to take physical measurements of forage quantity and quality.
“Clipping of quadrats is the most accurate way of measuring forage production, stated Mark Moseley, USDA Natural Resource Conservation Service (NRCS) Range Conservationist at Boerne, Texas. “A quadrat or frame can be made from steel rod or ¼-inch pipe. I use an 11.5 inch by 22 inch frame which equals a 1.92 square foot area. Select locations that represent the average forage production for the pasture and randomly throw the quadrat a distance of approximately 10 to 15 feet for each clipping. Work the frame through vegetation to the ground in the spot where it lands. Take a photograph of the vegetation in the frame from an angle and sun position that offers the best perspective when viewed. Clip, at ground level, the vegetation rooted within the boundaries of the frame. Only harvest current year’s growth and place each sample in a pre-weighed paper bag. Weigh each sample using a gram scale. Sample quadrats until there is confidence that a representative sampling has been obtained, usually 10 clippings. Because forage moisture content varies, it is recommended that samples be dried and the dry weights used to calculate carrying capacity.”
Photographs taken of the quadrats are compared with the weights to help train you to estimate forage production. They are also helpful in determining production trends from year to year.
Rocky Lemus, Extension Forage Specialist at Mississippi State University, recommended that forage dry matter be determined using a microwave oven. He provided the following procedure:
- 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 reweigh it.
- If forage does not feel completely dry, reheat it for 30 seconds. Reweigh 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.
- Calculate the average dry weight of all collected samples and convert to pounds per acre by multiplying the number of grams by 50.
“Native rangeland forage production varies with each range site,” said Hoyt Seidensticker, rancher and consultant at Sisterdale, Texas. “Range sites are classified based on soils (depth, texture, plant growth limiting factors), topography, current vegetation and precipitation zone. When grazing capacity is being determined, each range site is evaluated separately.”
“Once you know the amount of forage on a grazing site, a suitable stocking rate is calculated,” stated Seidensticker. “An animal unit (Table 1) consumes approximately 30 pounds of dry-weight forage per day or three percent of their body weight. Total amount of forage required per animal unit is approximately 30 pounds dry-weight times the number of days the pasture will be grazed. A good rule of thumb is still, ‘graze half – leave half.’ So you are going to allow your cattle to eat only 50 percent of the available forage. Another 25 percent is ruined from trampling, defecation and bedding grounds. This leaves 25 percent of the available forage for grazing which means that the total available forage needs to be divided by 4. This figure needs to be divided by the amount of forage needed per animal unit to determine the grazing capacity.”
Table 1. Animal Unit Equivalents
|Kind of Animal||Class of Animal||Number of Animal Unit Equivalents|
|Cow & Calf||1000 lb & < 4 mos.||1.00|
|Long Yearling Cattle||12 -17 mos.||0.80|
|Short Yearling Cattle||7 – 12 mos.||0.60|
|Adult Female Goats with Kids||———————–||0.17|
|Weaned Kids to Yearlings||———————–||0.10|
|Mature Ewes with Lambs||———————–||0.20|
|Weaned Lambs to Yearlings||———————–||0.12|
Although these procedures seem tedious and time consuming, they should be followed until forage production can be accurately estimated by simply walking through the pasture. Grazing capacity should be determined for each season of the year and anytime there are significant changes in weather patterns.
Do you consider animal units in your grazing plans? If so, what method or information do you use?