Ohio Agronomy Guide, 14th Edition

Bulletin 472-05

Chapter 9: Pasture and Grazing Management

David J. Barker and R. Mark Sulc

Livestock have unique effects on pasture that vary from the effects of mowing on forage. Factors such as selective grazing, uneven defoliation, manure, treading, and the variable energy requirements of livestock make grazing management complex. Balancing these sometimes conflicting effects takes a good understanding of soil – plant – animal interactions that can best be gained from knowledge, practice, and experience.

Pastures are often the most economical way to provide forage for ruminant animals. A 50% reduction in feed costs can be achieved during the grazing season with well-managed pastures. Lowering feed costs is especially critical in livestock production systems that have a small margin of return, such as cow-calf enterprises. In such systems, techniques to extend the grazing season (especially into November and December) can keep costs to a minimum. Even on dairy farms, however, where pasture comprises a significant portion of the forage program, feed costs have been reduced by an estimated 50 cents to $1.00 per cow per day during the grazing season. Although grazing systems usually have lower production per animal, the reduced costs usually result in grazing systems being profitable.

Productive pastures that provide good animal performance do not happen by accident. They are a result of careful planning and sound management. To achieve profitable returns from a pasture program, the manager must have knowledge of animals, plants, and soils and be able to respond to their needs. This chapter aims to introduce the basic principles and practices involved in grazing pastures for profitable animal production.

Grazing Systems

The goal of a grazing system is to provide sufficient pasture of appropriate quality for livestock throughout the grazing season. Major feed deficits that occur in winter and during drought in summer can be offset by feeding forage conserved from the surplus in spring or growing drought-tolerant forages such as summer annual grasses. Forage species differ in their periods of growth and utilization (Figure 9-1 and Table 9-1), and these differences can be exploited to optimize the length of the grazing system for a particular enterprise. Cool-season pastures are the foundation of pasture systems in Ohio. Permanent cool-season pastures can be supplemented with semi-permanent cool season pasture (e.g., hayland providing temporary supplemental pasture), perennial warm-season pasture, and annual pastures (e.g., brassicas, small grains, annual warm-season grasses). There is no one best combination of types of pastures. It is important to maintain flexibility when designing pasture systems, because needs and conditions change from season to season and year to year.

Figure 9-1. Seasonal patterns of forage production/utilization. (lb DM/ac/day.)

Pasture areas can also be stockpiled (left ungrazed) during certain seasons to accumulate forage for grazing when pasture production is not sufficient to meet animal needs. For example, birdsfoot trefoil can be stockpiled in the spring to be grazed during the summer slump in pasture production. Most commonly, tall fescue is stockpiled during late summer and fall for late fall and winter grazing. Stockpiling pasture provides available forage during seasons when low productivity of pastures might force the producer to feed hay or sell livestock.

The varying nutritional requirements of livestock add to the complexity of a grazing system. Within a season, livestock will require different amounts and quality of forage depending on their physiological state. For example, dry cows and early pregnancy cows have a low nutritional requirement, with their diet only needing to meet their maintenance requirement. Lactating females have an energy requirement two to three times greater than non-lactating females. The timing of calving/lambing has a large impact on the demands on forage supply; traditional systems will have peak demands coincide with spring forage production, however, there are many exceptions to that pattern. Young livestock have a higher requirement than mature (male and dry female) livestock. Balancing the nutritional requirements of diverse groups of livestock within a season requires considerable skill and planning.

Stocking Rate

The most important variable for grazing management is stocking rate. No grazing system can adjust for a long-term mismatch between total forage supply and forage consumption. Grazing management means controlling the frequency and intensity of grazing by livestock (Table 9-2). These each have unique effects on individual pasture species, livestock intake, and the resultant forage production.

Controlling grazing pressure is important to maintain desirable forage species in pastures. Long periods of low grazing pressure typically cause a loss of legumes from the stand, because they are selectively and frequently grazed, which weakens the plant (new regrowth is grazed off). Long periods of high grazing pressure may result in temporary or long-term decreases in pasture productivity and loss of desirable species from the stand.

Grazing Management

The most controversial debate among graziers is the comparison between continuous and rotational grazing.

• Continuous grazing involves stocking a (usually fixed) number of livestock in a large area for a prolonged (more than two-month) period. Animals have a high degree of selectivity during the first part of the grazing period. If the grazing period is too long, plants grazed at the beginning of the grazing period are likely to have regrowth that is grazed off again before the grazing period ends, resulting in reduced plant productivity.



• Rotational grazing involves fencing a pasture into several smaller sections called paddocks so that only one paddock is grazed at any given time while the remainder of the pasture is rested. This subdivision of the pasture area puts the manager in control of the grazing pressure. Putting the herd in a small paddock results in rapid utilization of available forage. Once the paddock is grazed to the desired degree, animals are moved to a fresh paddock. This grazing of paddocks in sequence allows forage in each paddock to rest between grazings; thus, the forage plants are able to regrow and renew energy reserves for vigorous regrowth.



• Management intensive grazing (MIG) is a form of rotational grazing that usually involves 20 to 40 paddocks with grazing periods of one to five days. The most intensive rotational grazing systems have two to three moves per day. In these systems, there is more control of what the animal eats and normally better growth and persistence of desirable pasture plants. The stocking rate is very high within one paddock (high grazing pressure), usually resulting in high utilization. The manager must be careful to move animals to the next paddock when the available pasture falls below its optimum range.

In general, begin grazing tall grasses when they are seven to eight inches tall and remove animals when grass has been grazed down to a three-inch height or less. Begin grazing short grasses, such as Kentucky bluegrass, when they are five to six inches tall and remove animals when grass is grazed down to a one- to two-inch height. These general guidelines should be modified based on the predominant pasture species. Highly productive dairy animals may need to be removed from paddocks before the plants reach these heights, or milk production levels are likely to fall. In such situations, an excellent grazing management practice is to let highly productive animals (such as lactating cows) topgraze the paddock first, followed by a lower producing group of animals (such as dry cows) to clean-up by grazing the paddock down to the desired height.

When managing a rotational grazing system, stocking rate and available pasture should be optimized. Growth rate of the pasture varies depending on the season, weather conditions, and soil productivity. Consequently, in most pasture systems, growth rate varies among pasture areas. Rest periods need to be flexible and should be based on the growth rate of the pasture (Table 9-2). It is best to not use a rigid rotational scheme, but to move animals to those paddocks that have reached their optimum available pasture (optimize forage quantity and quality). Spring management usually involves diverting some of the pasture acreage for hay or silage production to use the excess forage growth produced.

There are numerous combinations of grazing frequency (rotation rate) and grazing intensity within grazing systems (Table 9-2). There a few ‘rights’ and ‘wrongs’ with grazing management, and graziers need to find a system that satisfies their overall objectives. Some commonly recommended grazing frequencies and intensities for different seasons are shown here. It should be noted that within a farm with fixed area and stocking rate, increasing the grazing frequency (i.e., a slower rotation) will also result in closer grazing. Pastures can compensate from an intense grazing by having a longer period for recovery. As a generalization, we use fast rotations during periods of high pasture growth rate, and slow rotations during periods of slow growth rate. Repeated and close grazing (i.e., overgrazing) can only occur on isolated paddocks, or on an over-stocked farm. Infrequent and lax grazing (undergrazing) can only occur on isolated paddocks, or on an under-stocked farm.

The species and class of grazing animal may determine the grazing period. Since lactating dairy cows need consistent quality forage, their grazing period may be anywhere from a half day to two days. Beef cows, brood ewes, and most other ruminants do not require as consistent quality forage, and longer grazing periods should suffice.

The advantages of rotational grazing systems include less grazing selectivity, better nutrient dispersal, familiarity with the livestock and regular field inspections (because of more frequent pasture visits), ease of switching an area to hay/silage conservation, better control of forage utilization, ease of quantifying livestock intake (pre- and post-grazing yield measurement), and maximization of intake on taller forage. There are also disadvantages that include the need for more fencing, more water sources, and more time spent with stock movement (typically daily). Also, livestock can be forced to eat forage they might have otherwise rejected.

Contact your county Extension office for resources available to assist you in developing a rotational grazing system.

Feed Budgeting

Inventory control is an essential component of any business, including a grazing system. While measurement of the merchandise on-hand might be easy for many businesses, it is more difficult (but not impossible) for a grazing farm. In an ideal system, the rate of forage growth matches the rate of intake by livestock, but life is seldom ideal. With grazing, there are distinct periods of surplus forage (in spring) and of deficit forage (in summer and winter). Grazers expect these surpluses and deficits and have strategies in place to address those events. In addition, other climatic variables such as a cooler spring, wetter summer, or late fall can present opportunities for grazing once they are identified. A well-monitored grazing system should have targets for farm cover (available forage) for every month of the grazing season and a monitoring system to ensure targets are met.

Pasture can be measured using various systems, including eye estimation, pasture height and the conversion of 300 lb per inch (400 lb/inch for perennial ryegrass and Kentucky bluegrass), rising plate meter, and pasture meter (e.g., capacitance). Measurement of each paddock on a farm is suggested on a one- to four-week basis, and most farmers monitoring this data employ a computer to take care of the many calculations. One estimate calculated that one hour per day invested in feed budgeting could increase annual farm profit by $6 to $48 per cow.

Improving Production

When developing a pasture improvement program, the producer should begin by considering his or her goals and the resources present. A pasture’s current condition and its anticipated use should determine whether to reestablish, renovate, or leave the pasture as is. It usually is not necessary to tear-up existing pastures to improve productivity. Many pastures can be improved without renovation simply by implementing good grazing management, controlling weeds, and applying lime and fertilizer where needed.

Improvements in forage production are of little benefit unless there is also an increase in farm stocking rate. Often, identifying the correct stocking rate is the most important attribute of a grazing system. Increases in forage production can result in a small increase in per-head performance of livestock; however, such increases usually have a minor effect on farm profitability compared to the benefits resulting from additional livestock. In grazing systems we need to think more about product per acre, than product per animal.

Fertilization

Fertilization is usually the easiest management practice for increasing pasture production (Table 9-1). Good fertility usually enables earlier spring grazing, extends the pasture season, increases pasture quality, and is more profitable. Good soil fertility is usually necessary to retain the most productive species. A soil test is the best guide for proper fertilization. In pasture, 20 to 50 samples should be taken throughout the area to be tested, avoiding manure piles since these have enriched nutrient status. Pastures frequently have low pH, phosphorus (P), potassium (K), and nitrogen (N). Each nutrient needs to be considered separately.

Soil pH is a measure of soil acidity. Soils with a pH less than 5.5 can be a problem for certain pasture species, and correction with lime is recommended. Responses of pastures to lime are similar for hayed forages and are addressed in Chapter 7.

Phosphate fertility is necessary to encourage legume growth. In general, legumes are less competitive for P than grasses, due to having fewer and coarser roots. One unique aspect of grazing is that P is enriched in dung piles, and some researchers argue a lower efficiency of P fertilization under grazing. Over time, however, P achieves an equilibrium, and recommendations for P in pastures are similar to hayed forages (see Chapter 7).

Potassium fertilizer requirements are frequently less for pastures than for hayed forages. Potassium comprises 2% to 4% of forages, and losses anticipated with hay removal should be corrected by fertilizer application. Potassium losses under grazing are much less, and fertilization according to a soil test will address any requirements.

Nitrogen fertilization requirements in pastures depend a great deal on the legume content. Many pastures vary from hayed meadows by having a significant legume content. If legumes constitute more than 35% of the pasture, then nitrogen is not recommended, because the legume contributes adequate nitrogen through nitrogen fixation. In the absence of legumes, nitrogen is the most limiting factor to growth of pasture grasses, especially the tall-growing species. Pasture grass yields can be increased two- to five-fold by adequate fertilization with nitrogen. Nitrogen can also be strategically used to stimulate extra growth during certain seasons. An example is late summer nitrogen fertilization of tall fescue to stimulate fall growth for stockpiling. For more details on nitrogen fertilization, refer to Chapter 7, Forage Production.

Nutrients should cycle naturally in a well-managed pasture through nitrogen fixation from legumes and livestock excrement. Usually 80% or more of nutrients ingested by livestock are excreted back onto pasture. Additional fertilizer is required to compensate for nutrients that might be exported from a pasture as milk or meat.

The distribution of recycled nutrients through grazing animals is dramatically affected by grazing management. An assessment of the uniformity of animal manuring across the pasture should be made before crediting the returned nutrients to the entire pasture acreage. Soil test every three to four years to monitor changes in fertility status across pastures.

Weed Control

A properly maintained pasture promotes a vigorous sod that competes well against most weeds. Good grazing management will control many weeds simply by defoliation; sheep and goats are exceptional bio-control agents! Not all weeds are detrimental, and some weeds can be beneficial to livestock by having a high mineral content. There are commercial grazing varieties of some species, such as chicory and plantain, that once were considered weeds. Some weed problems can develop from overgrazing, treading damage, poor fertility, or pH problems. Correcting these cultural aspects of pasture management will frequently result in effective control. Occasional mowing helps reduce invasion by woody perennials. Clipping weeds in the bud to early bloom stage weakens them by depleting root reserves and preventing seed production.

Herbicides should only be used to control serious weed problems in pastures (refer to Bulletin 789, Weed Control Guide for Ohio Field Crops). Only poisonous, noxious, and thorny weeds warrant specific control. If weeds are widespread, broadcast applications are needed; if weeds occur in patches, spot spraying is more appropriate and less costly. Because most broadleaf herbicides remove desirable legumes from pastures, minimize their use. Once weeds are controlled, avoid spreading manure contaminated with weed seeds, clean equipment after working in weed-infested pastures, and keep fence rows free of problem weeds.

Pasture Renovation

In many situations, introducing desirable legumes and productive, palatable grasses into pastures is worthwhile. Renovation techniques further improve pasture stands without completely destroying the existing sod. Newly renovated pastures should be grazed less frequently and less closely for 12 months, to prevent them from reverting to their former state. More details on forage species adaptation, seeding rates for mixtures, and establishment guidelines are given in Chapter 7.

When renovating pastures, the existing sod must be suppressed sufficiently to allow new seedlings to become established. Three basic techniques of pasture renovation are outlined here. The success of these methods depends on adequate soil fertility and proper pH. Soil test a year prior to renovation and apply nutrients as needed to correct any deficiencies.

• Limited tillage—Disk or other tillage implements disturb the sod enough to destroy 30% to 50% of the stand and expose the soil. When the tillage is performed in the fall, lime and fertilizers can be partially incorporated. Seed is broadcast or drilled on the pastures in late winter or early spring. Graze or mow the pasture to reduce competition from surviving pasture plants or weeds after seeding. Manage the stand so that seedlings can absorb plenty of sunlight. Mow just above the new seedlings. Control grazing and stocking rates during the establishment year to favor regrowth.



• No-tillage with chemical sod control—Herbicides suppress the existing sod during establishment of introduced species. Close grazing the previous fall helps reduce spring vigor of the existing stand. If perennial or biennial broadleaf weeds are a problem, the pasture can be sprayed the previous fall with broadleaf herbicides (refer to Bulletin 789, Weed Control Guide for Ohio Field Crops). Then, in the spring, use paraquat to burn down the sod when two to three inches of new growth are present and seed as soon as possible after applying the herbicide. Use a no-till drill designed to cut through the sod and place the seed shallow and in good contact with the soil.



• Frost seeding—Sod control is essential, using heavy grazing the previous fall to weaken and open up the sod when tillage or chemical control of the sod is not used. Seed can be sown in late winter through early March, while the soil surface is still freezing and thawing. The freezing and thawing promotes good seed-soil contact. Germination occurs with warming soils. This technique is most successful with the clovers; red clover and ladino clover, in particular, are two of the easiest legumes to establish using this method. Frost seeding is less reliable for grasses, and should only be attempted for rapid-establishing species such as ryegrass. Frost seeding is also more successful when pastures are dominated by bunchgrasses, such as orchardgrass, rather than by dense sod-formers, such as tall fescue and Kentucky bluegrass.



• Use high-quality seed—Plant high-quality seed of adapted cultivars at the recommended rates. Inoculate legumes with the proper N-fixing bacteria. Use one of the seeding methods described earlier to achieve good seed-soil contact and proper seeding depth. Many seedings fail because of poor seed placement and lack of timeliness in planting.



• Pest control—Insecticide treatments may be beneficial, particularly when seeding alfalfa into old pastures. Refer to insect control guidelines for no-till seeding in Chapter 7.

First-Year Management of Renovated Pastures

Manage the pasture carefully after seedling emergence to minimize competition from the established sod. Use light, periodic grazing to prevent the existing sod from overtaking the new seedlings. Grazing periods should be short (less than one week), and animals should be removed when the new seedlings begin to be grazed off. For example, graze closely when the existing sod has three to four inches of new spring growth, then graze again when regrowth is six to eight inches. If tall, stemmy regrowth develops, mowing may be necessary. Throughout the summer, graze the pasture rotationally.

Pasture Species and Cultivar Selection

Many pasture species provide forage for grazing animals. In Ohio, we are fortunate to have diversity in adapted forage species. Species use should be based on suitability for the soil, animal enterprise, and the planned grazing management of the farm. Tables 7-1 and 7-2 in Chapter 7 outline the agronomic adaptation and characteristics of some of the more important forages grown in Ohio.

For many forage species there are now cultivars that are specifically bred for grazing systems. Most especially, alfalfa that is included in a grazing system should be one of the grazing-tolerant varieties. For white clover, new varieties that are more branched and with smaller leaves are more persistent under grazing than the larger, ladino varieties. For orchardgrass, the smaller and more densely tillered varieties are sometimes preferred for grazing. Ask your seed supplier if grazing varieties are available and consult performance data under grazing currently being published by some Midwestern university forage-testing programs.

Cool-Season Grass Species

Cool-season grasses begin growing early and produce considerable forage in the spring. In the summer, higher temperatures and moisture stress reduce production. Production increases slightly in the fall with normal moisture supply, and growth ceases by mid-October to mid-November (Table 9-1). If earlier spring grazing is desired, apply 50 lb nitrogen per acre in March. In most situations, early spring N should be applied to a very limited acreage, because it will make it even more difficult to manage the late spring flush of growth that occurs most years. Cows soon to freshen or with calves should have access to a magnesium-containing mineral supplement to help prevent grass tetany on pasture in the spring. Avoid application of potassium to pastures in the early spring to reduce this risk.

Kentucky bluegrass usually volunteers over time in pastures. To hasten the establishment of bluegrass in pastures, seed may be planted in early spring or late summer and early fall. Kentucky bluegrass can withstand close, continuous grazing and tends to be more abundant under sheep and horse grazing. Although it tolerates poor fertility, its forage quality and production are greatly improved if pastures are limed and fertilized with phosphorus and potassium and rotationally grazed to favor companion legumes (Table 9-1).

Orchardgrass is well-suited for grazing. In the spring, begin grazing when plants are four inches tall. Graze orchardgrass heavily and frequently (every 10 to 12 days) during the flush spring growth. Leave a three- to four-inch stubble so the grass can recover quickly. Harvest surplus pasture for hay or silage. Orchardgrass can tolerate continuous grazing if the plant is not grazed below three to four inches, but production will be lower than if rotationally grazed. Allow at least three weeks between summer grazings for best recovery.

Perennial ryegrass is one of the highest quality grasses and is excellent for use in creep grazing pastures for young animals. Initial spring grazing can begin when growth reaches a height of three to four inches and soils are dry enough to prevent excessive treading damage. Allow six to eight inches of regrowth between grazings for improved yield and persistence. Established perennial ryegrass tolerates continuous grazing if a two-inch stubble is maintained; however, rotational grazing improves production. Perennial ryegrass does not stockpile well in winter, and nitrogen applications in fall can reduce plant survival over winter. Ryegrass pastures should be grazed to a three-inch stubble in late fall to prevent smothering and development of snow molds that can kill plants.

Reed canarygrass should be grazed hard in the spring. Maintain growth below a height of 12 inches during the rapid spring growth. Short duration rotational grazing with heavy grazing pressure results in the best use and greatest animal gains per acre. Do not graze closer than three to four inches above the ground. Reed canarygrass can tolerate continuous grazing, but productivity will be much greater under rotational grazing that allows at least three weeks of recovery between summer grazings.

Smooth bromegrass produces palatable, nutritious pasturage. Begin grazing in the spring before the stem elongates significantly. Loss of stand occurs when bromegrass is grazed off in the jointing stage (stem elongation) during stressful growing conditions and under high nitrogen fertilization. Best production in pastures is achieved with rotational grazing that allows three or more weeks of recovery. Smooth bromegrass tolerates moderate continuous grazing, but production is lower.

Tall fescue should not be grazed closer than three to four inches, and recovery periods between grazings improves persistence and production. Tall fescue produces very palatable forage in the fall. It is the best grass for stockpiled forage for winter feeding. When stockpiling tall fescue, remove animals by early August and apply 50 to 60 lb N per acre in August if increased yield and quality of stockpiled forage is desired (Table 9-1). For more information, refer to Stockpiling Tall Fescue for Winter Grazing, Ohio State University Extension Fact Sheet AGF-023, available at: www.agcrops.osu.edu . There are new soft-leaved varieties that have improved palatability for livestock. Endophyte-free and non-toxic endophyte varieties are recommended in preference to varieties with ergovaline-producing endophytes.

Timothy can be grazed if carefully managed, and it produces palatable, high-quality pasturage. Begin spring grazing when grass is three to four inches tall. Rotational grazing with at least three weeks of recovery results in good production and persistence. In the spring, timothy is relatively tolerant of grazing before stem elongation (jointing stage). It is adversely affected by harvesting or grazing during the jointing stage, as is smooth bromegrass.

Festulolium is a true hybrid between ryegrass and meadow fescue that has characteristics intermediate between the parent species. Festulolium has a dense ryegrass-like pasture growth habit that has better quality than fescue, and is more hardy than ryegrass. The density of the sward is especially attractive for grazing.

Small grains provide late fall and early spring grazing. Refer to Chapter 7 for details.

Other forage resources can be used in a planned full-season grazing program. Examples include corn stalks grazed after grain harvest and hay stockpiled in pastures.

Legumes

Legume species are highly desirable components of productive, economical pasture systems. Alfalfa, clovers, birdsfoot trefoil, and annual lespedeza all provide high-quality forage for grazing and eliminate the need for nitrogen fertilizers. Many legume species are deep-rooted and more tolerant than grasses of summer moisture shortages. Legumes generally improve animal performance and increase carrying capacity of pastures.

Pasture systems containing legumes require more careful management than pure grass pastures. Most legumes will not persist under continuous grazing and must be grazed rotationally. Fertility requirements are higher for most legume species. Pasture management practices should favor legumes because of the difficulty of maintaining them in the system. Grazing must be managed carefully to prevent bloat when grazing pastures where legumes predominate. Exceptions are birdsfoot trefoil and annual lespedeza, which are non-bloating.

Alfalfa should be rotationally grazed with short grazing periods (four to five days). Alfalfa can be grazed beginning in the late prebud stage in the spring if the stand is vigorous. Start grazing no later than the bud stage for improved utilization of the available forage. Allow recovery periods of 24 to 30 days between grazings under favorable growing conditions; therefore, four to five subdivisions (paddocks) are needed to provide adequate rest periods for this species. Less recovery time is required when grazing than for mechanical harvesting. By grazing at earlier stages of growth, the leaves remaining after grazing are still active and will support regrowth. Animals should be removed from alfalfa when soils are wet to prevent excessive crown damage.

Red clover provides excellent animal gains and can be grazed beginning in the late vegetative stage in the spring. Rotational grazing management should be practiced, with short grazing periods (less than seven days) and recovery periods of 28 to 35 days. As red clover stands begin to thin out in the second or third year, pastures can be managed like pure grass stands. The red clover component in pastures can be maintained by reseeding (with a drill or frost seeding) every two to three years. Natural reseeding can be enhanced if stands are allowed to go to seed.

Birdsfoot trefoil can be grazed in the spring when it reaches the bud stage of growth. Best production and persistence is achieved with rotational grazing that allows 28 to 35 days of recovery after grazing. Close, continuous grazing damages the stand because regrowth of trefoil is dependent on sufficient leaf area being present to capture sunlight and produce energy. Because carbohydrate reserves are low in birdsfoot trefoil roots during the growing season, it should not be grazed shorter than three inches. In emergencies, it can tolerate several weeks of continuous grazing if a three- to four-inch stubble height is maintained. Grazing should be managed to allow birdsfoot trefoil plants to go to seed every two to three years to maintain its persistence in pastures. Individual plant persistence is poor because of susceptibility to Fusarium-type crown and root rotting organisms. Reseeding can be accomplished by stockpiling spring growth until July.

White (ladino) clover can be grazed continuously or rotationally once established. Although it can be grazed to a one- to two-inch height, closely grazed plants need time to recover. If grown with tall-growing grasses and grazed rotationally, the pastures should be grazed at relatively short intervals (every 21 days) to prevent excessive shading by the grass.

Alsike clover must be allowed to reseed itself to maintain its presence in pastures, otherwise it lasts only two years. If grown with tall grasses in pastures, the pastures should be grazed at short intervals to prevent excessive shading by grasses.

Annual lespedeza can be used effectively in pasture renovation to improve animal performance and late summer forage production, especially in endophyte-infected tall fescue pastures on acidic and low phosphorus soils. Do not graze after early September to allow sufficient seed production for stand regeneration.

Other Species

Switchgrass, big bluestem, Indiangrass, eastern gamagrass, and Caucasian bluestem are warm-season species that complement cool-season species by providing forage during the summer months when the cool-season grasses are less productive. Rotational grazing is necessary for good persistence of these species. They should not be grazed below six to eight inches in height during the growing season and should be grazed less frequently than other forages to ensure recovery from grazing. Overgrazing of basal tillers jeopardizes the regrowth potential of these grasses. Caucasian bluestem tolerates closer grazing than the other species. In general, these warm-season species have low protein concentrations and should be planted with clover to ensure livestock have sufficient protein intake.

Sudangrass, sorghum-sudangrass hybrids, and pearl millet are annual warm-season species that are ready for grazing about six weeks after seeding. They are well suited as supplemental forages during hot, dry periods when perennial cool-season forages are less productive. They must be grazed rotationally with short grazing periods (less than two weeks) to avoid prussic acid poisoning. Refer to Chapter 7 for grazing guidelines.

Forage chicory is a relatively new forage crop in the United States, but it has been used in other countries for centuries. This perennial plant is suited to soils that are well or moderately well drained with medium to high fertility and a pH of 5.5 or greater. Chicory produces leafy growth that is high in nutritive value and mineral content if managed properly. One farmer reported his milk yield increased four lb per cow per day when grazing a new pasture that was dominant with chicory. It has a larger taproot and provides excellent summer forage for grazing animals. Chicory requires nitrogen fertilization for good production.

Chicory production is optimized under rotational grazing management. A stubble height of 1.5 to two inches should remain after grazing. After the seeding year, chicory grows vigorously and attempts to produce stems in late spring and early summer. Stubble heights greater than 1.5 inches and rest periods greater than 25 days allow stems to elongate rapidly (bolting). Sometimes grazing can keep stems below a six-inch height in late May, but if this is not possible, a single mowing during July can keep the plant in a leafy state. There are three to four grazing varieties marketed throughout the United States.

Forage brassicas are fast-growing, productive, and highly digestible annual crops. These crops offer great potential and flexibility for improving livestock carrying capacity from August through December. Spring-seeded brassicas boost forage supply in late summer. Summer-seeded brassicas extend the grazing season in late fall and early winter. Refer to Chapter 7 for details.

Mixtures

One unique aspect of livestock is their preference for pasture mixtures. Although livestock prefer some species over others (e.g., clover over grasses), when given the option, livestock will select a diet from a mixture of species. We call this the buffet principle, and when applied to humans, dietary intake is greatest when there is maximum choice (e.g., at a buffet). There is some evidence this principle also applies to livestock grazing mixtures.

Other benefits of mixtures are based on biodiversity theory. That is, when we use a mixture of species, we can increase the resilience and resistance of the resulting grassland when faced with variation in fertility, climate, and other stresses. For example, a mixture could include a combination of drought-hardy species that would be able to maintain some production during summer as well as species that provide early spring production when moisture is abundant.

The converse argument is that every species has a specialization that is best expressed in a simple pasture composition. A pasture manager might include a series of specialist pastures for particular purposes on the farm—for example, a field of tall fescue because it has superb characteristics for stockpiling in winter. Whether we employ mixtures of species within a single pasture, or mixtures of different pastures within the variable topography of a farm, we should use the benefits of species diversity wherever possible.

Toxicity

It is unfortunate that almost every forage species has some potential for toxicity. In the majority of cases toxicities occur in isolated instances, and can be treated and managed as they occur. Some of the most significant toxicities include:

• Bloat—Perhaps the most significant feed disorder for grazing. Bloat is caused by foam that is produced by saponins in most legume species. Unable to escape, the foam distorts the rumen and, if not treated, can result in death. Although there are many theories about causes of bloat, there are no fool-proof recommendations or approaches. Equally, there are many exceptions where animals graze legume-rich diets without event.

  The best guidelines are to be extra observant when grazing pastures with more than 20% legume, restrict animal access to legume pastures on an empty stomach (especially during the main morning grazing when dew might still be present), feed fibrous forage (rough pasture or hay) prior to grazing legumes, and restrict grazing intervals on legumes to less than two hours. Anti-foaming detergents in water systems, applied to pasture, or administered orally, can reduce the occurrence of bloat. Tannin-containing legumes, such as birdsfoot trefoil, do not cause bloat.

  Susceptibility to bloat is an inherited trait, and livestock that bloat should be culled and not used for breeding (including bulls).

• Endophyte—This is a fungus that is found in tall fescue, perennial ryegrass, and some other less common grass species. The fungus confers some benefits to the grass, such as drought tolerance and insect resistance, but also produces alkaloids (especially ergovaline) that are detrimental to livestock. The U.S. forage industry has adopted a standard of providing endophyte-free tall fescue and ryegrass varieties; however, these sometimes have poor persistence or can become re-infested with endophyte-infected tall fescue.

  Re-infestation of endophyte in pastures after seeding endophyte-free varieties can occur through natural reseeding of surviving infected plants in the pasture, through infected seed carried in by animals previously grazing infected pastures, and through feeding infected hay in the pasture. A revolution in the forage industry has been the discovery of new fungal races that do not produce ergovaline. These non-toxic endophytes seem to confer the benefits of regular endophytes, but without any toxic effects.

• Nitrate toxicity—This is largely a problem of warm-season annual species (sorghum-sudangrass) but has been reported for many other vigorous species. The problem is most likely to occur when grazing the early flush regrowth following relief from drought and when grazing frosted forage. Grazing by livestock during these risk periods should be restricted to one to two hours per day, after which time livestock should be moved to safe feeds. The risk period usually passes after two weeks.

• Alkaloids in reed canarygrass—Varieties of reed canarygrass older than 20 years have the potential to accumulate alkaloids that are toxic to livestock. Modern varieties have had the active agents removed and are safe to graze. Old stands of reed canarygrass should only be grazed for short periods, and livestock intake diluted with safe forages.

• Hypomagnesemia (tetany or staggers)—This is a disorder resulting from an imbalance (deficiency) of Mg, compared to Ca or K. This is most common in newly lactating dairy cows with a high loss of Mg in milk. The condition occurs rapidly (as short as several hours after calving) and is most effectively treated by intravenous injections of Mg. Forage conditions increasing the likelihood of staggers include low magnesium in forage ( less than 0.2%), high Ca and K levels, and in rapidly growing forage (after N application, or during spring). Some new grazing varieties have been selected for higher Mg levels to reduce hypomagnesemia. Ask your pasture seed supplier if these varieties are available and suitable for your area.

• Slobbers—This is an uncommon disorder resulting from livestock ingestion of Rhizoctonia bacteria that can grow on legumes during warm moist conditions. The condition is not life-threatening, but is unsightly in show animals. Slobbers can be treated by removal from infected forage and allowing free access to water.