Question of the Week
Answer: Cattle are selective grazers. If given a choice they will only eat the highest quality, most palatable plants in the pasture. In order to ensure that plant biodiversity and high nutritional status is maintained in the pasture it is necessary to set up a grazing management system to better control livestock grazing. The elements of controlled grazing are (1) timing and (2) intensity of grazing. This means controlling the number of animals and how long they are in a pasture.
Consider developing a rotational grazing system to take full advantage of the benefits of nutrient cycling as well as the ecological balance that comes from the relationships between pastures and grazing animals. High density stocking for short periods helps to build soil organic matter and develops highly productive, dense, resilient pastures. For more information see ATTRA’s Rotational Grazing and Paddock Design, Fencing, and Water Systems for Controlled Grazing. Also available is Jim Gerrish’s Management-intensive Grazing: The Grassroots of Grass Farming, available from Green Park Press.
A rotational grazing management plan need not be complex. It merely has to direct the grazing animal to eat when and where you want them to in order to keep the plants in their growing (vegetative) stage. The basic principles of rotational grazing management include:
1. proper timing of grazing (corresponding to plant physiological stage)
2. proper intensity of grazing (duration on the pasture)
3. residue or plant height after grazing.
In order to efficiently utilize the dry matter available, a rotational grazing system should be implemented. Rotational grazing allows for more effective forage utilization by increasing herd size on smaller paddocks for a shorter time, thereby decreasing grazing selectivity and giving the farmer more control on what and when the livestock eat.
It is important to allow the pasture plants to get to sufficient height prior to turning the cattle onto the pasture. By waiting until the grass is 5 to 10 inches high, depending on species, the roots have become well developed and the plants can handle defoliation. Grazing intensity, or duration, can be taken care of by designing a suitable rotational grazing system. Rotational grazing, as the name implies, involves moving the cattle periodically from pasture or paddock to paddock. For instance, a good rule of thumb is to split a pasture into 10 or more paddocks (see guidelines for number of paddocks and paddock size below) with electric wire or electric tape, and stock each paddock heavily for a short amount of time. By doing this you are forcing the cattle to eat all that’s there, including weedy plants they might otherwise not eat. However, before the animals eat the plants to the ground, you move them to the next pasture. This takes into account the third principle. It’s important to leave several inches of grass to allow adequate leaf area for subsequent regrowth. Depending on the species, you will need to leave from 2 to 6 inches of plant stubble at moving time. An 11-paddock rotational grazing system that allows animals to graze each pasture for 3 days will give each paddock 30 days of rest (These figures are for planning purposes, and it is recommended to move according to forage height rather than by the number of days on pasture). Most grasses will need 15 to 50 days of rest between grazing events to allow adequate regrowth, depending on season, moisture, and plant type.
Calculating Paddock Size and Number
Two questions that will immediately come up for someone contemplating a rotational grazing system are (1) how many paddocks should I have, and (2) how big should the paddocks be? Essentially, answers to these two questions can be easily acquired by utilizing the following formulas:
To calculate the number of paddocks needed, use the following formula:
Paddock Number = Rest Period (days) /Grazing Period (days) + number of animal groups
Paddock Number = 30 days / 2 days + 1 = 16 Paddocks
Then, to calculate the size of each paddock in acres, use this formula:
Paddock Size = Daily Herd Forage Requirement X Days in Grazing Period / Lbs. Available Forage per Acre
Considering that growing steers will generally consume around 2.5% of their body weight, we will estimate the intake of one hundred 700 pound steers to be 17.5 pounds per animal per day, times ten animals equals 1750 pounds daily herd forage requirement. If the animals will be in each paddock for two days, and the available forage in the paddock is 2000 pounds per acre, then,
Paddock Size = 1750 X 2 / 2000 = 1.75 acres
Therefore, for a herd of one hundred 700 pound steers, and grass availability of 2000 pounds per acre, you would need 16 paddocks of 1.75 acres each, allowing for two days of grazing in each paddock before moving them to the next paddock. It is very important to realize, however, that 2000 pounds per acre is not the total productivity of the paddock, but reflects only the amount of forage the animals will be allowed to consume. A dense pasture in good condition will produce approximately 400 pounds of forage for each inch of plant height. So if you plan to begin grazing when the grass is 10 inches tall, and move the cattle when the grass is 5 inches tall, you should only calculate the 5 inch difference in height in your paddock size calculations. In our example, 400 pounds per inch X 5 inches = 2000 pounds per acre of available forage.
The figures and interpretations in this example are highly variable, and your situation will likely be different from this or any other grazing plan. This example is intended to familiarize producers with the basics of developing a rotational grazing system.
It is important to remember that overgrazing is not really a function of how many animals are on a pasture, but how long they remain there. In grazing management, time is the most important factor to consider in establishing a grazing system for sustained forage production. Continuous grazing allows livestock to selectively graze the most palatable plants over and over. The problem with this isn’t necessarily in the selective grazing activity, but in the fact that the grazed plant does not get the time to regrow before it is grazed again. New growth is more palatable and contains more nutrients than older growth, so animals will come back for a second and third bite as long as they are in the pasture, resulting in the most palatable forages being killed out.
A grazing system should allow the animal to be in the pasture long enough to take only that first bite. Frequent movement from pasture to pasture is a way to ensure that all plants have ample time to re-grow after grazing. In addition, for pastures with adequate water during the growing season, a very high stock density encourages animals to graze the pasture more uniformly than if the pasture was lightly stocked. In this situation the "weedy" species are being grazed at the same intensity as the "good" species.
Determining Forage Yield
Forage yield can be determined with a (1) pasture ruler or (2) a rising plate meter. A pasture ruler is just that; a ruler calibrated in inches placed on end at ground level, with forage height measured in inches. A rising plate meter measures density as well as height. A 20 X 20 inch plate weighing 2.6 pounds is dropped on a rule at waist height. For this measure in Iowa and Missouri, each inch of forage height equals 263 lb/ac DM, and has been verified by numerous clip and weigh field studies. This measure should be calibrated for local conditions by clip and weigh method to obtain accuracy.
A good rough estimate is 300 pounds of dry matter per acre per inch on a ruler. This measure is likely to have a 50 to 80 percent accuracy depending on if you have calibrated your measurement procedure. Jim Gerrish’s values range from 150 pounds per acre per inch in a fair stand to 600 pounds per acre per inch in an excellent stand as determined by clipping and weighing numerous quadrants and comparing them to sward heights (Gerrish, 2004). The vast differences in the above estimates reflect differences in pasture types. For example, bermudagrass will most likely be different from bromegrass when measuring stand density with a ruler or rising plate meter.
References and Resources
Forage Information System
A comprehensive website for forage-related topics, including publications, educational opportunities, and professional resources. Maintained by Oregon State University.
Grazing Systems Planning Guide
Kevin Blanchet, University of Minnesota Extension Service
Howard Moechnig, Natural Resources Conservation Service
Minnesota Board of Water & Soil Resources,
Jodi DeJong-Hughes, University of Minnesota Extension Service
University of Minnesota Extension Service Distribution Center,
405 Coffey Hall, 1420 Eckles Avenue, St. Paul, MN 55108-6068 firstname.lastname@example.org
Delineates the components of a grazing system by taking the farmer through the grazing management planning process. You can also view/download it at www.extension.umn.edu/distribution/livestocksystems/DI7606.html.
Management-intensive Grazing: The Grassroots of Grassfarming
Jim Gerrish, Green Park Publishing
This book can be obtained through The Stockman Grassfarmer’s Bookshelf at 800-748-9808.
The industry-standard for growing and managing pastures for sustained livestock production.
Donald M Ball; C S Hoveland; Garry Lacefield
Altanta, Ga.: Potash & Phosphate Institute: Foundation for Agronomic Research, ©1991. Third Edition 2002.
Pastures for profit: A guide to rotational grazing
Cooperative Extension Publications, 45 N. Charter St., Madison, WI 53715
Grazing ecology, and setting up a rotational grazing system.
The Economics of Organic and Grazing Dairy Farms
Regional Multi-State Interpretation of Small Farm Financial Data from the Fourth Year Report on 2003 Great Lakes Grazing Network Grazing Dairy Data. Madison, WI: UW Center for Dairy Profitability. Kriegl, T. 2005.
Fact Sheet #1: Project Overview
Fact Sheet #2: Comparing the Top Half with the Bottom Half of Graziers
Fact Sheet #3: Comparing Herds by Size. Less than 100 Cows vs. 100 Cows or More
Fact Sheet #4: Comparing Seasonal Calving with Non-seasonal Herds
Fact Sheet #5: Grazing vs. Confinement Farms.
Fact Sheet #6: Preview of Financial Performance of Graziers by Breed
Contact: Tom Kriegl at 608-263-2685 or
277 Animal Sci Bldg
1675 Observatory Dr.
Madison, WI 53706
Comprehensive research project comparing conventional and pasture-based dairy farms in the Midwest. An excellent resource for dairy farmers considering a transition to organic and/or pasture-based production.
Organic Dairy Farming: A Resource for Farmers (2006)
Jody Padgham, editor.
Midwest Organic and Sustainable Education Service
PO Box 339, Spring Valley, WI 54767
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