Matching Livestock and Forage Resources in Controlled Grazing
Many of the important management decisions a livestock producer makes relate to the management of the forage resources of the land unit. Both biological and economic efficiency are influenced by a producer's ability to match animal type and nutrient needs to forage availability and quality on a year-round basis. This article addresses grazing objectives, how forage management decisions can influence animal performance, and how the type of operation and animal management decisions influence efficiency of performance on pasture.
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There are four general objectives of grazing management, from the forage standpoint. The producer uses the grazing animal to achieve each of the objectives.1. Maintain botanical balance: Intensity of grazing impacts the competition between species of plants. An example is maintaining a legume with a cool season grass where keeping the height of grass down favors the legume. This point alone justifies some type of rotational grazing system. The primary reason tall fescue is so predominant is the persistence of the grass under poor management conditions. A grazing system using a simple 3-6-pasture rotation allows other plants to compete with fescue, yielding a diversity of forages that can enhance productivity. Most producers cannot keep an adequate stand of legumes without using some type of rotational grazing system that will allow the legumes to reseed.
2. Encourage rapid growth: The main consideration is having adequate leaf area for photosynthesis and storage of nonstructural carbohydrates.
Grazing a plant too short will limit the rate of regrowth because of limited leaf area. Inadequate rest for the plant after grazing will limit storage of carbohydrates and may decrease persistence. Plant growth also slows as the plant matures. Grazing the top of the forage off will also encourage more rapid growth and delay maturity. From the animal perspective, grazing the forage when it is too short decreases intake because the animal cannot get a "mouthful" of forage with each bite. For cool season grass-legume pastures, if forage is 6-10 inches tall, the animal has high intake. When the forage height is less than 3-4 inches, then intake decreases by half. The specific height at which intake becomes limited is different for bermuda grass because of the density of the growth but the relationship is similar. Therefore, in order to ensure enough leaf area for rapid growth and to maintain high intake by the grazing animal, we should avoid grazing the pasture too short.
3. Compromise between yield and quality: This objective will come up quite often throughout this paper. Naturally, yield is influenced both by "uncontrollable" factors, including rainfall distribution, soil type, and management factors such as fertility and species. The key to yield is to be able to estimate forage availability at any point in time, and manage that forage to have the quality needed by the grazing animal. Quality is primarily determined through grazing management by attempting to keep the forage in a vegetative state. A producer must understand the nutrient requirements of the various groups of animals being grazed and manage accordingly. In this regard, it is important to note that the quality parameters used to evaluate hay are less meaningful when evaluating the forage available to the grazing animal, because the animal is selectively grazing, and because grazing behavior and forage availability have a greater impact on intake than quality.
4. Minimize mowing: A potential expense for beef producers is clipping pastures. In some circumstances animals can be used to minimize that effort. Multi-species grazing (e.g., sheep and cattle) is effective. Also some weeds (e.g., ragweed) are very nutritious and palatable in an early vegetative growth stage. Clipping of pastures is usually most needed under continuous grazing. The utilization of forage is decreased when mature forage is clipped and, therefore, wasted. This can be prevented with a good grazing program.
The most effective way to accomplish the above objectives is to adopt some form of rotational or controlled grazing. In this regard, item three can be broken down into two specific objectives of controlled grazing. The first is increased forage utilization. Research indicates that controlled grazing can increase forage utilization from around 30 percent (under continuous grazing) to 60-75 percent for a 20-40-paddock rotation. This is primarily because animals are used as "mowers" and the frequency of rotation determines the amount of urination, defecation, trampling and bedding down animals do on a pasture, all of which contribute to decreased utilization of available forage. A greater stock density decreases selective grazing and spot grazing. Occurring primarily under continuous grazing, spot grazing allows some areas of pasture to mature while other areas are overgrazed.
The second objective of controlled grazing, and the one with the greatest potential impact, is maintaining better quality forages. Species of forages with higher potential quality yet more demanding management requirements (e.g., orchardgrass-alfalfa, bromegrass or endophyte-free fescue with a legume) have greater persistence in a forage system involving controlled grazing. Also, forage growth can be more carefully managed and kept in a vegetative state under controlled grazing, thereby improving forage quality. A controlled grazing program that prevents seedhead formation and maintains a more vegetative forage should reduce (though not eliminate) the impact of tall fescue toxins, as high-endophyte fescue seed contains substantially higher levels of potential toxins than the fescue leaves. This should also reduce competition with other non-toxic forages.
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Feed profiling is a concept used by New Zealand producers in matching their resources to the type of livestock enterprise best suited to the pattern of expected pasture production. A feed profile can be used to determine the appropriate stocking rate and when best to calve (lamb, kid, etc.) or when to sell surplus stock or purchase new stock. The ability of the farm to meet the nutritional requirements of the animals through pasture is evaluated by estimating potential production and anticipated feed demands of the livestock.
Adjustments in management can be made on a short-term (budget) or long-term (profile) basis. When a feed shortage or surplus appears to be developing, a feed budget can be used to determine the deviation from the profile, and short-term decisions made as to how most profitably to use the surplus (cutting hay, adding animals) or overcome the deficit in a least cost manner (feed supplement, fertilize with nitrogen, wean animals, sell animals, etc.). A feed budget is accomplished by estimating the pasture availability, pasture production during the period, and the animal demand. A practical approach to a deficit may be to accept lower performance of animals because of decreased intake.
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There are several types of livestock producers to consider when discussing grazing management. Beef cattle production, from the grazing standpoint, involves the cow-calf producer and the backgrounder. The producer most concerned with maintaining high quality pasture is the dairy producer who has decided to cut costs by allowing total production to decrease utilizing pasture more. Another set of producers are raising sheep and meat or dairy goats, while some landowners who include wildlife or agroforestry in their land-use plan utilize grazing animals to achieve an ecological balance. Regardless of type of production, to survive economically each producer must evaluate his or her goals, determine how efficiency of production is impacted by forage resources, and make changes in management that decrease inputs.
Production systems for cow-calf producers are the most challenging in terms of matching forage resources to animal requirements. The first problem is the need for year-round production, and second is the effect of genetic variation on production potential among the wide array of breeds of cattle. Then, when the calving season component is added, choice of forages and grazing management becomes a complex issue.
In analyzing goals, the producer should first consider the desired weaning weight and milk production potential of the cows, and then attempt to time the calving date so that the highest quality forage is available at peak lactation and before breeding season. Work in New Zealand indicates that a producer can improve the efficiency of the cattle operation with a two-week change in calving season. Weight gain of the calf is influenced by the persistence of lactation and by forage consumption by the calf. Persistence of lactation is dependent upon forage availability and quality and is influenced by the genetic potential of the cow. Cows with high milk production potential will respond more to intensively grazed pastures managed for high quality. Cows with lower milk production potential might best be used in a system that utilizes a higher percentage of forage since their nutrient requirements are lower, reducing the demand for higher quality forage. Additionally, cows with high milk production potential probably should be calved in the spring or late winter, whereas cows of average milk potential might best be calved in the fall. Then the fall-born calves could be backgrounded through the summer, since the weaning weight of these calves would probably be less (at the same age) for a fall-calving herd than for a spring-calving one.
All herds have cattle with different nutrient requirements. Monitoring the condition scores of cows is important in determining the nutritional requirements of animals. It is probably good economical management to allow cows to lose weight at certain times of the year if the weight can be replaced with good pasture at another time without interfering with the reproduction of the cow. A forward grazing system can be used to graze animals with the highest nutrient requirements first, followed by cattle with lower requirements to "clean up" the pastures. This is particularly useful with two calving seasons when dry cows can follow lactating cows. Other examples include first-calf heifers followed by mature cows or the most productive cows followed by lower potential cows. Another strategy is creep grazing which gives calves access to higher quality forage than the cow.
Backgrounder (stocker production)
Greater per-acre economic potential of intensive rotational grazing can be achieved by backgrounding steers. This is primarily because 2-3 steers can be grazed where one cow-calf pair would graze. Also, steers will respond better to higher quality forage since milk of the cow tends to buffer calf gains, unless the cow needs to gain weight prior to breeding season.
Several factors are involved in matching the stocker animal to the grazing system. First are the anticipated market weight and/or date. Many producers are becoming interested in grazing cattle on fescue pastures until late June (dependent on forage availability) and then shipping to the feedlot. Pastures can be rested through the hot, dry summer months and another group of cattle backgrounded during the late summer and early fall months, allowing producers to turn two groups of calves each year. On the other hand, cattle that have been grazing high-endophyte fescue probably should go to the feedlot in the fall months rather than mid-summer. It might be more economical to allow cattle to "coast" through the summer, not worrying about gain, to allow them to go to the feedlot in cooler weather. Thought might also be given to putting cattle in feedlot earlier in summer, such as mid-May. An economic consideration in this case is that producers generally need to put 200 pounds of gain on cattle to make profit, and cattle moved out in May might not achieve a profitable amount of gain.
Another component is whether a producer is retaining ownership of his own calves or purchasing cattle. Controlled grazing can, because of the increased utilization of the forages, allow a producer to carry over calves without decreasing the number of cows. This point can be emphasized with the example of a producer with a fall-calving herd keeping calves through the summer to be sold as yearlings. Forage production during the summer is not utilized well with dry cows except to put gain on the cows before calving. With purchased cattle the critical issue may be when to buy and sell cattle to utilize the forage. Controlled grazing allows cattle to be on pastures earlier in the season. Also, forages such as summer annuals can be more economical when a higher degree of utilization is achieved. The desired market weight and date may be an important consideration in helping a producer decide whether to optimize return by grazing more for quality (higher gain per animal) or quantity (higher gain per acre).
Considerable interest is being expressed in dairy production on pasture, particularly in Wisconsin, New York, and Pennsylvania. Dairy production in New Zealand is accomplished without grain supplementation. Cows are rotated on pasture at least once a day and quite often twice a day. It has been suggested that a dairy cow can produce about 50 pounds of milk a day with only pasture if intake of high quality pasture is maintained at a high level. Accompanying the interest in production on pasture is seasonal dairying, where cows are lactating when forage availability is greatest and all cows dried off at the end of the grazing season. Consistent production of high-quality pasture throughout the grazing season is necessary as is a sound reproductive management program to ensure the cows are calving as a group within the time period that allows use of the pasture. A very intensive management program is required to optimize use of pasture. Also necessary is good pasture diversity, with choices of species that allow a consistent production of quality forage throughout the grazing season.
Sheep producers too are evaluating changes in management toward using more pasture and less harvested forages and grain. Changing the lambing season to April has the potential to allow considerable flexibility in production options. For example, nursing of lambs by grazing ewes, decreasing wintering cost of the pregnant ewe, or grazing weaned lambs to a market weight instead of pushing them on a high grain diet to reach market weight. A worthwhile consideration is to add sheep to other livestock enterprises for more efficient use of pasture. The grazing habits of sheep, goats, and cattle differ sufficiently that sheep and goats can be added to a cattle program without having to increase the landmass or decrease cattle numbers.
An increase in the production of goats for meat is anticipated to coincide with the apparent shift in diversity of populations. Goats can be used to control brush and weeds, and they more efficiently utilize pasture because they prefer browsing to grazing, but contrary to popular opinion, goats need higher quality forage than cattle because they cannot digest cellulose as well. Goats, because of their small mouths and prehensile lips, can select higher quality feed than cattle with their larger mouths. They eat in successive layers from the top of the plant to the bottom, so their intake in highly sensitive to pasture height and mass. Intake by goats drops when forage availability falls below 1000-1200 pounds of dry matter per acre.
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Animal type (size and milk production potential) as defined primarily through species and breed differences has a great influence on the nutritional requirements of animals. Therefore, the type of animal can impact the level of performance of the animal and the economic impact of a grazing system on different forages.
The grazing system influences the nutritional status of animals by affecting intake and quality of forage. Intake is decreased when pastures are grazed too short because the animal cannot get a "mouthful" with each bite. Regrowth of the forage is slower because the leaf area for photosynthesis is decreased. Additionally, the quality of the forage is lower.
Producer decisions, such as timing parturition to match the lactation curve to the forage production curve or choosing to graze steers rather than cow-calf pairs, should be considered in the choice of management decisions related to forage and grazing system. Choice of forages is also determined by nutritional needs of the animals being grazed. The nutritional needs of the animals being grazed should be considered for 365 days when determining the percentage of various forages used in the grazing system. Grazing different species together increases efficiency of forage utilization because of differences in behavior and forage/browse preferences.