Question of the Week
Answer: I am pleased to provide you with information on pasture stocking for beef cattle, dairy cattle, and goats in Iowa.
A general rule of thumb for stocking cattle on temperate pastures is one cow to the acre during the growing season, and rotating them periodically between pastures. For intensively managed systems, some Midwest dairy graziers are stocking about 25 cows per acre and rotating them every day to fresh forage. Your stocking rate will depend very much on how intensive your management system is. For this recommendation, I will assume that you will be implementing a controlled rotational grazing system, where animal density is high for a short period of time, and rest periods between grazing are long enough to allow for complete plant regrowth.
It is generally believed that six mature goats equal one cow on improved pastures and that ten goats equal one cow on browse or brushy areas. When grazing brush, it may be necessary to adjust stocking rates in order to accomplish your objectives. For example, when starting out with a very brushy area it might be desirable to stock two to four goats, or more, per acre. Later, as the brush disappears, some goats may need to be sold while a few (one-half to one goat per acre) are kept to control regrowth. These figures depend on the carrying capacity of the land. Observation and adjustment are necessary. Some producers, including Mr. Jim Willingham of 8 Mile Ranch near Uvalde, Texas, choose to allow the goats to harvest the brush as forage and maintain it as a renewable resource, rather than attempting to kill it (Coffey, 2006).
To successfully estimate stocking rate for pastures in Iowa, you will need to obtain information on (1) pasture productivity in tons or pounds per acre and (2) livestock nutrient and intake requirements. This letter contains information to assist you in determining these data and making appropriate stocking rate calculations.
Pasture Productivity for Iowa
Warm season pastures have the ability to yield 2 to 4 tons per acre of forage per year in areas of Iowa where they are adapted. Warm season grass species adapted to Iowa are eastern gamagrass, switchgrass, big bluestem, little bluestem, and Indiangrass.
Cool season pastures for Iowa include tall fescue, orchardgrass, timothy, smooth bromegrass, alfalfa, red clover, and birdsfoot trefoil. Cool season pastures consisting of grasses and legumes are highly productive and will yield as much as 7 tons of forage per acre per year.
Determining Forage Yield and Stocking Rate
Forage yield can easily be estimated with a pasture ruler. A pasture ruler is just that; a ruler calibrated in inches placed on end at ground level, with forage height measured in inches. “One estimate that has frequently been used to relate pasture height to its mass is the rough estimate of 200 lbs. of dry matter per acre per inch of height. This estimate will likely vary 50 lbs. per acre-inch or more based on grass type and season of the year. The height measurement is taken as the “natural, undisturbed height” of the pasture plants adjacent to the measure stick; not stretched or extended” (Barnhart, 1998).
Example: Consider an orchardgrass/legume pasture in good condition, with forage height of 10 inches on average. Orchardgrass should be grazed no closer than 2 inches, so that gives us 8 inches of grazable, high-quality forage. 8 inches of forage height times 250 pounds per acre (in average, good condition) yields 2000 pounds per acre of usable forage.
An 1100 pound cow will consume 2 ½ percent of its body weight per day, so that gives us a forage demand per cow of 27.5 pounds. 2000 pounds of forage supply divided by 27.5 pounds of individual cow forage demand equals 72 cows. This means that each acre of our example pasture has enough forage available to feed 72 cows for one day, or 36 cows for two days, etc.
To realize the efficiencies suggested by these stocking numbers, it is imperative that the farmer implement an intensively managed livestock grazing system. An intensive grazing system controls grazing such that, through high animal impact, the pasture is grazed to a prescribed height and the animals are moved to another pasture to allow complete recovery of grazed plants. The ATTRA publications Rotational Grazing and Paddock Design, Fencing, and Water Systems for Controlled Grazing contain more detailed information to assist farmers in setting up a controlled grazing system.
Another Method for Determining Stocking Rate
A simplified method for determining the initial stocking rate for a pasture of known acreage is to (1) estimate average yield per acre, (2) determine average animal weight, and (3) estimate the length of the grazing season in days. These figures can be used to determine the number of animals that can be grazed in the pasture for the season by using the following formula:
Number of animals = total acreage X yield per acre /
0.04 X (avg. animal weight) X (total days)
Example: Determine number of 1000 pound cows a 50 acre pasture will support for 100 days given pasture yield of 3000 pounds of dry matter per acre…
Number of animals =
50 acres X 3000 lb/ac /
0.04 X 1000 lb X 100 days = 37.5 cows
There are several key issues to consider when thinking about how many animals a pasture will support. Consideration must be given to forage production potential, utilization patterns by livestock, the nutrient content of the forage and forage growth patterns, the plant species that comprise the pasture, species diversity of the pasture plant community, and seasonal variations in temperature and moisture.
Forage Intake by Ruminants
Maintaining high forage intake is the most important thing a farmer can do to ensure high milk and meat productivity in grazing ruminants. Intake is the ingestion of feedstuffs by the animal, and is regulated palatability, foraging behavior, chemical characteristics of the feedstuff, forage quantity, density, and availability, dietary energy and fiber content, physiological stage of the animal, and temperature. For more detailed information on forage intake, see the ATTRA publication Ruminant Nutrition for Graziers, to be published in the fall of 2007. To obtain a draft copy of this publication, email email@example.com or call 800-275-6228 and ask for Lee.
Options for Increasing Intake on High Quality Pasture
High intake is one of the simplest methods of ensuring adequate nutrition for high producing ruminants. Ensure high forage intake by:
• keeping forage in the vegetative stage through grazing management,
• diversifying pasture composition to include several grass species, with around 30 percent of the pasture in legumes, and
• maintaining a dense pasture so animals will take larger bites.
Intake is maximized when pastures are:
• correctly stocked
• plentiful (8-10" tall for cattle, 6-8" for sheep)
• familiar to the animal
• fresh (not trampled or manured on)
Monitoring is the most neglected part of pasture management, and the most important. A good monitoring system will allow you to check how your management decisions are working on the ground. It will allow you to determine, for instance, if a particular grazing plan is having the desired effect over time. A monitoring plan will often involve quantifying a few important evaluation measures, such as plant species composition, percent cover, frequency of species, and forage yield. By comparing these measurements over time, you can start to see trends, and by comparing them to your grazing system, you can alter and adjust where you need to in order to arrive at your goals.
Record keeping is a very important part of pasture monitoring. In addition to recording physical measurements, keep track of when livestock enter and leave a pasture, what if any materials or chemicals are used, re-vegetation or weed control treatments, and observations on cattle health while in the pasture. This information will be extremely useful in refining your grazing plans.
References and Resources:
Barnhart, Stephen K. 1998. Estimating Available Pasture Forage. Iowa State University Extension.
Coffey, Linda. 2006. Meat Goats: Sustainable Production. Butte, MT: NCAT-ATTRA.
Gerrish, J. 2004. Management-intensive Grazing: The Grassroots of Grass Farming. Ridgeland, MS: Green Park Press.
Lyons, Robert K. and Richard V. Machen. 2001. Stocking Rate: The Key Grazing Management Decision. Texas A&M University.
Moore, K. J., T. A. White, R. L. Hintz, P. K. Patrick, and E. C. Brummer. 2004. Forages and Pasture Management: Sequential Grazing of Cool- and Warm-Season Pastures. Agron. J. 96:1103–1111.
Rinehart, L. 2006a. Pasture, Rangeland, and Grazing Management. Butte, MT: NCAT-ATTRA.
Rinehart, L. 2006b. Ruminant Nutrition for Graziers (unpublished manuscript, currently in editing and formatting). Butte, MT: NCAT-ATTRA.
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