(from Forages: An Introduction to Grassland Agriculture, 6th ed. Vol.1; Chapter 20: Grazing Management Systems, pp. 473-491)
A system is an integration of parts, thus grazing systems integrate the components of animal, plant, soil, environment, mangement, and other factors with the intent of accomplishing specific goals or outcomes.
Grazing systems are site specific, so they need to be described in terms of:
- Land: soil type, salinity, erosion potential and history, and fertility status
- Plants: species, varities, weeds, stage of growth relative to periods of use, percentage ground cover, forage mass
- Animals: number, kind, sex, size, production status, and age
- Management: intensity, grazing methods, number and size of paddocks, irrigation, fertilization, pesticide use, harvest events
- Location: latitude, longitude, elevation
- Climate: temperature, precipitation, humidity, season of the year.
Animals' and plants' responses and behaviours are different from that observed when managed alone. This is because each piece of a system behaves as a consequence of its relationships with other parts of the system. When that piece is managed in isolation away from the influence of the other system components, it is no longer under the same influences and may behave differently.
Grazing is usually the least expensive means of feeding livestock because costs of buildings, equipment, and labour associated with stored forages or purchased feeds are reduced or eliminated. It is almost always more profitable when livestock harvest their own feed. However, designing grazing systems that can ensure an adequate daily supply of forage for each animal on a year-round basis is challenging. Forage species differ in their season of growth and use. Livestock differ in their nutritional needs depending on their age, production status, or use for work. Matching the seasonal potential for quality and quantity of forage growth to the livestock's need for nutritional quality and feed quantity is one of the major challenges in grazing-system design. When successfully achieved, needs for harvesting or purchasing feeds are minimized or eliminated and profitability is generally improved.
Grazing systems must address many objectives:
- Provide the appropriate quality and quantity of forage for the livestock present.
- Ensure survival of the forage stands, promoting healthy, vigorous plant growth, and maintaining the desired botanical composition.
- Obtain the desired quality of life for the manager
- Protect the environment while conserving natural and nonrenewable resources.
Increasingly, other objectives also must be considered:
- Develop and protect wildlife habitat
- Sequester carbon from the atmosphere
- Reduce soil loss from wind and water erosion
- Protect water quality and quantity, animal health and welfare, animal product quality and safety.
- Protect aesthetic value and open space
- Offer hunting, eco-tourism, or recreational opportunities
In the future, integrating grazing systems with cropping systems may offer one of our best opportunities to manage and protect our natural resources while providing an economic return and maintaining needed levels of food and fibre production to meet the needs of an increasing global population. (Why, this is already happening, particularly with what is called crop-residue grazing or aftermath grazing.)
Grazing Management
Grazing management involves manipulation of the soil-plant-animal complex to achieve the desired results.
Grazing management can be made more intensive or more extensive. Intensive grazing management uses additional inputs of resources, labour, or capital to increase livestock production per acre or per head or to improve forage production and utilization. Extensive grazing management uses lower optimum inputs of labour, resources and capital to achieve profitable and sustainable plant and animal production.
More or less intensive systems are not "good" or "bad." In fact, managers do not simply choose between extensive and intensive systems, they select from a continuum of possible inputs that might include more managerial time, more fertilizer nutrients, more fencing, or other inputs. Choices are influenced by assessment of input costs in relation to the value of the anticipated productivity increases and economic return. The inputs chosen first are often those judged to be most limiting, i.e., those with the greatest likelihood of increasing productivity or efficiency of production. Many weather, soil, plant, animal, and environmental impact considerations must enter into the decision.
Management strategies and intensity of management must also fit the lifestyle goals and abilities of the manager. Systems that demand intense management will not work well in situations where circumstances compete for time and energy required to manage such systems no matter how well suited the system may be in other respects.
Nomenclature of Grazing Systems
The term animal unit(AU) was developed to facilitate comparison of different kinds of livestock. An animal unit is defined as an 1100 lb (500 kg) nonlactating mature cow (Bos taurus) fed at maintenance or its equivalent in other kinds and classes of livestock. Defining the equivalent presents challenges and has been the subject of much debate. An often used general rule of thumb suggests that five ewes (Ovis aries) are equivalent to on mature cow or one horse (Equus cabalus).
A more exact way to equate livestock is on the basis of metabolic body size, generally accepted as the animal's weight in pounds to the 0.75 power (BW0.75). Thus, 1 AU = (1100 lb)0.75=233. An 882-lb animal developed to equal 197, or 0.85 AU (197/233=o.85). This mathematical approach was developed to equate animals based on their body surface area rather than their true body weight. It is based on the assumptions that heat loss is more nearly related to body surface area than to body weight and that, expressed on this basis, heat loss is a constant for all species. Using this formula, comparisons have been made literally from mice to elephants.
Forage mass is the amount of forage dry matter per unit land area at a single point in time. Forage yeild is the total mass of forage produced per unit of land area over a period of time. Forage allowance is a relationship between forage mass per unit area and the number of animal units at any given point in time. At high allowance levels, each animal as a large amount of forage available from which to choose its diet. Performance per animal generally increases as forage allowance is increased up to some point, after which it will level off.
Stocking rate is an animal-to-land relationship measured over a defined time period. Stocking density refers to the animal-to-land relationship at a single point in time. Grazing pressure is a ratio of animal units to forage mass. When grazing pressure is low (i.e., few animal units per unit of forage mass) forage supply exceeds animal needs. Individual animal performance may be high due to selective grazing and/or optimum bite size, but output per unit of land area is decreased because forage is wasted. In this case, increasing grazing pressure may increase output per unit area. However, as grazing pressure continues to increase, performance per animal and per acre will begin to decline.
Grazing Methods
Grazing methods are grazing management procedures designed to achieve specific objectives.They are used to achieve specific defoliation strategies for plants or to allocate nutrition to different classes of livestock. They may influence nutrient recycling or be used to discourage trailing, a social behaviour in which cattle move in single file, forming paths of bare soil that can lead to soil erosion or streambank degradation. There are many grazing methods: rotational and continuous stocking, creep grazing, first-last grazing, sequence grazing, strip grazing, buffer grazing, frontal grazing, and others. No one grazing method is the best. Each is designed to accomplish specific objectives; thus, choosing the correctt method is critical to success. Indeed, several different grazing methods are usually included within a grazing system.
Continuous and Rotational Stocking
Continuous stocking allows livestock unrestricted and uninterrupted access to a specific area for a specific time. No subdivision fences are used during this period. Continuous stocking does not imply season-long use and may in fact be a fairly short period, but it does require intentionally defined period. In response to changes in forage supply during the period of use, the manager can add or remove livestock, increase the total size of the area being grazed, or provide supplemental feed to maintain the desired forage-to-animal level.
Rotatonal stocking implies recurring periods of grazing among two or more paddocks with periods of rest and regrowth for the forage between defoliation events. Grazing periods can be shortened or lengthened to achieve optimum forage management. When forage productivity is high, rotational stocking allows the harvest of some paddocks for hay or silage before they become overly mature. When growth slows and additional forage is needed for grazing, some or all paddocks are reinserted into the rotation. Normally, a paddock is grazed until 70% to 80% of the available forage has been utilized or when remaining dry matter substantially limits intake (500 lb/acre). Forage utilization is usually somewhat lower with continuous stocking, typically stocking, typically 55% to 65%.
Rotational stocking is particularly useful for forage species that benefit from rest periods. For instance, most alfalfa cultivars persist better and yield more with about 4 weeks between grazing cycles due to their cyclical use and replenishment of root and crown nonstructural carbohydrates. Alfalfa is generally sensitive to defoliation periods that extend into this carbohydrate replenishment phase, which normally begins after shoots reach a height of about 6 inches. Grazed continuously, alfalfa plants can be weakened, become less competitive with grasses, or even die. However, grazing-tolerant alfalfa cultivars perform better under continuous stocking than traditional alfalfa cultivars.
During other times of the year, continuous stocking may be preferable for alfalfa. If autumn temperatures are sufficienctly cold to prevent alfalfa regrowth, forage that accumulated during late summer and early autumn can be stocked continuously without harming the alfalfa. Giving animals access to the entire pasture at this allows selective grazing of alfalfa before freezing damage causes excessive leaf and quality losses.
Buffer Grazing
Pasture supply is not constant throughout the year due to growth habit and environmental effects. One approach for adjusting forage supply with continuous stocking is to use temporary electric fencing to exclude livestock from part of the area, which can be harvested later if it is not needed for grazing.
Closing off a variable area gives the flexibility to accomodate low production in a case of drought, high production, or changing animal demand. As the season progresses, the temporary fence is moved forward or backward to adjust the amount of forage available for grazing.
Strip Grazing
Strip grazing confines animals to an area to be grazed in a relatively short period. Stocking density is high enough to utilize the available forage quickly, usually in 0.5 to 7.0 days. This grazing method is particularly applicable to forage crops where no growth is expected during grazing. Utilization is high with this grazing method, up to 80% to 90%, because grazing takes place quickly on a small portion of the total area, reducing waste due to trampling and fouling.
Strip grazing should not be confused with rotational stocking. Strip grazing is a method of allocating forage and does not imply rest, recovery, and reuse of the area.
Creep Grazing
Nutritional needs of livestock differ among production stages and animal objectives. Beef cows need high nutrition in late gestation, during breeding, and during the first 4 months of lactation. In contrast, the nutritional needs of ewes increase 6 to 8 weeks before lambing but needs for peak lactation occur just after lambing. Nutritional level of ewes should be increased again prior to breeding to improve conception races.
Nutrient intake and milk production by the cow or ewe during early lactation is very important to the offspring, but as milk production declines, nutrient requirements also decline. On the other hand, the nutrient requirements of the offspring are increasing during this time. Research has demonstated that feeding the cow or ewe above nutrient requirements does not improve performance of the offspring. Only about 65% of the potential weight of calves weaned at 8 months of age is attributable to milk production by the cow. Research in Virginia demonstrated that daily gains of calves increased by 80% when they were creep fed in addition to milk compared with calves that had milk only. Feeding cows to gain during this period did not improve calf performance.
Creep grazing partitions feed nutrients between the dam and its offspring by allowing calves to graze areas from which cows are restricted. The calves can selectively graze highly palatable and digestible plant parts to optimize intake and increase gains. Cows graze an area that, while providing adequate quality and quantity to meet their lower nutritional needs, forces them to utilize a higher percentage of forage dry matter. BEcause an ample supply of high-quality creep forage is provided directly to the calf, cows can be forced to utilize their pasture more completely by consuming lower quality plant growth.
A creep gate with openings large enough to allow offspring to pass through can be placed between the base pasture grazed by dams and the adjoining creep paddocks. To encourage their use, creep grates should be placed in areas frequented by the livestock. The forage species used in the creep area is less important than providing a sufficient quantity of vegetative, leafy, high-quality forage to allow selective grazing and maximum intake.
First-Last Grazing
First-last grazing divides the forage in a paddock into higher- and lower-quality portions by sequentially grazing with two or more groups of animals with different nutritional requirements. First-last grazer groups can even be different livestock species.
Forage quality of most pasture swards is stratified, with the highest-quality forage at the top of the canopy and the lowest-quality forage at the bottom, nearest the soil surface. When introduced into a new paddock, animals also selectively graze the upper portion of the canopy first. Thus, the first grazers, animals with high nutritional requirements, such as lactating dairy cows or finishing lambs or cattle, utilize only the best-quality upper portion of the plant canopy. This maximizes selective grazing and bite size, ensuring these animals both the highest quality and intake-potential forage. This group moves forward to the next paddock before their nutrient intake becomes restricted.
The last grazers are then brought in to graze forage left behind by group one. Last grazers should be animals with lower nutritional requirements, such as dry cows or cows in late lactation. The lower dry matter intake and nutrient requirements allow these animals to perform adequately in spite of the reduced quality and quantity of the remaining forage.
Mixed Grazing
Mixed grazing combines two or more animal species in the same grazing system. The animal species may graze the area together or separately, at different times. Mixed grazing can be useful in altering parasite cycles. Increasing the period when a particular species is off the pasture helps because parasite eggs gradually die over time. Rejection of forage due to fouling with dung and urine is also reduced in mixed grazing systems because animals are less prone to reject forage fouled by another species. Mixed grazing also takes advantage of differing animal preferences for forage species, canopy heights, and chemical composition characteristics. Goats, for example, prefer to browse which helps control woody and other weed species that are rejected by cattle. Instead of representing a weed control cost, mixed grazing controls those weedy plants while using them in livestock production.
Sequence Grazing
In sequence grazing, two or more land units differing in forage species and composition are used in succession. Each unit can be subdivided for rotational stocking or they can be grazed contrinuously. This may help in matching forage quality and quantity with livestock needs. In a grazing system based on monocultures or a single mixture, all paddocks would have the same response to environmental stresses.
Different forage species or mixtures may have peak production at different times or may be more heat or drought tolerant, and thus improve the seasonal distribution of production compared with a single species. Cool-season and warm-season forage species have different temperature optima for growth, and, thus, provide forage at different times of the year.
Frontal Grazing
Frontal grazing takes advantage of animal behaviour. This method uses a sliding fence moved by the livestock as they push to gain access to ungrazed forage. Grazing efficiency can be high due to uniform use and less trampling of ungrazed forage. Manure is more evenly distributed as livestock advance across a field.
For frontal grazing to work well, a relatively flat pasture free of trees and topographical features that would impede forward movement of the fence is needed. When appropriate, frontal grazing may increase grazing days per acre due to efficiency of forage use, but it does not normally increase individual animal performance compared with either continuous or rotational stocking.
Stockpiling
Stockpiling is a forage management technique by which forage produced during a period of higher production is allowed to accumulate to be grazed later, when growth rates are lower. Some forages lend themselves better to this management than others.
Tall fescue is well suited to this management strategy and is commonly hayed or grazed in early August and about 60 lb of N/acre are applied. Livestock are excluded while the tall fescue grows during late summer and autumn. During this period, temperatures are declining but conditions are usually favorable for forage growth. Nitrogen encourages growth and leaf production, whcih promotes photosynthesis. Lower temperatures slow respiration more than photosynthesis, so nonstructural carbohydrates accumulate.
By early November, there is typically about 1 to 2 tons/acre of high-quality fescue forage available for grazing. Leaves of tall fescue, at vegetative stage in fall, can often be 2 to 3 ft long. On average, 1 acre of stockpiled fescue and about twenty 50-lb bales of moderate-quality hay will provide the feed nutrients need to maintain one beef cow through the winter. With freezing and thawing in late winter, quality of the stockpiled tall fescue will decline, and it may be desirable to have some good-quality hay to supplement livestock even when forage is still available for grazing, particularly if cows are calving during late winter.
Warm-season grasses can also be stockpiled for winter grazing and their potential should not be overlooked. Examples include bermudagrass, old world bluestem, switchgrass, or forage sorghums. Qualtiy is usually lower than for cool-season grasses. Warm season grasses become dormant during autumn and do not accumulate nonstructural carbohydrates. Phosphorus and sulfur are particularly likely to be deficient for animal needs when warm-season grasses are stockpiled.
Considerations in Developing Grazing Seasons
The ability of a grazing animal to ingest needing nutrients is influenced by animal factors, chemical and phyical attributes of the plants, sward characteristics, environment, and management. Many factors affect nutritive value of the forage. In general, legumes such as clovers and alfalfa and cool-season annual grasses, including annual ryegrass and the small grains wheat, oats, barley, and rye, are highest in quality. Cool-season perennials such as orchardgrass and smooth bromegrass rank second, while warm-season perennials, including bermudagrass and old world bluestems, are lower in nutritive value. There are many exceptions, however. Growth stage, canopy morphology, environmental conditions, and other factors greatly influence forage quality and animal performance.
Nutrient requirements vary among different kinds and classes of livestock. The highest-quality forages are generally most appropriate for lactating dairy cows, finishing cattle or sheep, preweaned calves, lambs, or foals, and animals at hard work. Breeding stock and growing animals have a more moderate nutrient requirement, while mature, nonworking or producing animals and dry cows or ewes have the lowest nutrient requirements to simply maintain these animals.
A key goal of any grazing system is to match forage quantity and quality with animal requirements. Seasonal dairying, for example, is based on late winter calving to match early lactation of cows with the high quality and quantity of forage normally available during spring in humid temperate regions. By the time forage quality and growth rates decline later in the season, peak lactation has passed and nutrient demand by cows is lower. Cows are dry and have lower forage quality and quantity requirements during winter when grazing is scarce.
Systems should be designed to minimize supplemental feed needs, but almost all systems will require some supplementation during periods of low forage growth. This could be forage harvested previously during times when forage growth rate exceeds livestock demands. Crop residues such as corn or grain sorghum stalks; co-products from other industries, such as stems, leaves, and burrs removed during the ginning process for cotton ("gin trash"); distillers' grains; or other plant and animal industry co-products can provide valuable supplemental feed for livestock as well.
Grazing system design must consider fixed factors such as climate, amount and distribution of precitipation, the soil types, and perhaps the capital available to invest. Other factors, such as forage species, soil fertility, and soil pH, usually can be modified. Cool-season perennial forages for the basis of grazing systems in much of the northeastern US, while warm-season perennials should for the basis of systems in the southeastern US and throughout much of the West. Warm-season forages may complement a cool-season base or cool-season forages may extend grazing for a system based on warm-season perennials.
Grazing systems should be easy to manage and have sufficient flexibility to accomodate varying environmental, market, and production conditions. There are many ways to build flexibility into systems. Buying and selling animals may offer opportunities to match forage demand with forage growth. Stored or stockpiled forages buffer against times of low forage growth.
Successful systems should do the following;
Widely used livestock fences include high tensile wire (electrified or not electrified), barbed wire, electrified tape or wire, various types of woven wire, and specialized types such as board or stone fences. They differ widely in initial cost and maintenance requirements. The best choice depends on the economics, availability of materials, durability requirements, and specific safety concerns, and the ability of the fence type fo accomplish its specific purpose.
Barbed wire is generally avoided for horse pastures because the aggressive, nervous behaviour of horses can result in fence-related injuries and because some horses have high individual animal value. Electric fences are less effective for sheep because their wool provides a natural insulation, but these fences can help to control predators such as coyotes. Fences are less expensive and should be minimized. Less fencing material is needed to surround a square or circle than other shapes with the same unit land area enclosed. The system and the landscape should dictate the needs for fencing, and the system should be designed before the fences are built.
Nutrient Management Considerations
Grazing animals remove in their bodies or in animal products, such as milk, only a small proportion of the N and minerals contained in ingested forage. For example, a 650-lb steer contains only about 5 lb of P. In contrast, a 5-ton per acre yield of alfalfa hay that averages 20% crude protein and 0.3% P will remove 320 lb/acre of N and 30 lb/acre of P. Nutrient export may be desirable to remove excessive nutrients. Conversely, pastures require far less fertilizer inputs to maintain fertility than do areas where hay or silage is produced.
Most of the nutrients consumed by grazing animals are excreted in urine and feces. Woodmansee found that 83% of the N in forage grazed by steers was returned, excreted in urine and feces. Most urinary N is readily available to plants, while feces N is primarily in organic forms that must be mineralized by microorganizms before becoming available for plant uptake. About 30% to 50% of the N voided by grazing animals is volatized and lost to the atmosphere as ammonia. Phosphorus is excreted mostly in the feces. The value of waste nutrients from grazing livestock for forage growth is reduced by their typically uneven distribution over the pasture surface. Factors including landscape features, position of and distance traveled to water, and grazing system design can influence distribution patterns of manure and urine.
Nitrogen and P are currently the nutrients of primary concern in environmental pollution. Application of large amounts of animal wastes from confinement feeding have increased concerns about excessive levels of soil P in recent years. Phosphorus is relatively immobile in soils and accumulates to levels well above the needs of plants or animals. Excessive soil P contributes to pollution of surface waters primarily through direct movement with eroded soil particles.
Nitrogen follows many different pathways through the soil-plant-animal sysytem and is subjected to losses through leaching, volatilization, denitrification, and erosion. Once in the soil, other forms of N can be quickly converted to nitrate, which is highly water soluble. Leaching of nitrate into water presents health hazards and volatilized N forms can contribute to air pollution and odor problems. Nitrous oxide, produced during denitrification, is a greenhouse gas and contributes to ozone depletion. Nitrate con also accumulate in plant tissues when soil levels are high. Nitrate in excess of 0.25% in forage raises concerns for animal health, and levels above 0.5% should be considered potentially toxic. Including legumes with grasses contributes N and decreases or eliminates the need for N fertilizer, but it does not necessarily prevent nitrate leaching primarily due to recycling of N through the grazing animal.
Livestock Water Considerations
Although livestock obtain some water from snow, dew, and moisture in forages, an adequate suppy of good quality water is essential to maintain animal health performance, and feed intake. Animals consuming green, succulent forage have decreased water consumption, while dry feeds and high salt or protein intake increase water consumption. Water consumption increases as temperatures increase. For example, a 900-lb lactating cow consume about 11.4 gallons of water per day when the temperature is about 40 F. Daily water consumption increase about 16.2 gallons/day when temperatures rise to about 90 F. Cattle grazing in steep, rough terrain should not have to travel more than 0.5 mile per day to obtain water, while those on level or rolling land should not have to travel more than 1 mile. Giving livestock direct access to streams, ponds, and other waters sources can kill bank and border areas (riparian) vegetation, push soil into the stream, and contribute to water pollution.
Designing Forage/Livestock Systems
A good place to begin designing forage/livestock systems is to evaluate land resources and the climate. These are features that cannot be altered easily. Next, assess what forages are best suited to these conditions: First, in general terms, whether the system should be based on cool-season or warm-season forages and the extent to which the base can be complemented with less well suited forages that could help fill feed gaps. Then, in terms of specific forage specie that might be used. What are the livestock requirements and when will peak feed needs occur? To what extent can the period of maximum feed requirement be matched with the time of greatest forage supply? How will periods of forage deficits be filled?
In regards to systems for different animal species besides cattle, these same principles can still be applied in designing the right forage/livestock systems for you. A key factor is to understand the nutritional need, behaviour, and production goals for the animals and to understand why and which forages are adapted, when they offer opportunities for use, and how they must be managed. Then--put these together.
A system is an integration of parts, thus grazing systems integrate the components of animal, plant, soil, environment, mangement, and other factors with the intent of accomplishing specific goals or outcomes.
Grazing systems are site specific, so they need to be described in terms of:
- Land: soil type, salinity, erosion potential and history, and fertility status
- Plants: species, varities, weeds, stage of growth relative to periods of use, percentage ground cover, forage mass
- Animals: number, kind, sex, size, production status, and age
- Management: intensity, grazing methods, number and size of paddocks, irrigation, fertilization, pesticide use, harvest events
- Location: latitude, longitude, elevation
- Climate: temperature, precipitation, humidity, season of the year.
Animals' and plants' responses and behaviours are different from that observed when managed alone. This is because each piece of a system behaves as a consequence of its relationships with other parts of the system. When that piece is managed in isolation away from the influence of the other system components, it is no longer under the same influences and may behave differently.
Grazing is usually the least expensive means of feeding livestock because costs of buildings, equipment, and labour associated with stored forages or purchased feeds are reduced or eliminated. It is almost always more profitable when livestock harvest their own feed. However, designing grazing systems that can ensure an adequate daily supply of forage for each animal on a year-round basis is challenging. Forage species differ in their season of growth and use. Livestock differ in their nutritional needs depending on their age, production status, or use for work. Matching the seasonal potential for quality and quantity of forage growth to the livestock's need for nutritional quality and feed quantity is one of the major challenges in grazing-system design. When successfully achieved, needs for harvesting or purchasing feeds are minimized or eliminated and profitability is generally improved.
Grazing systems must address many objectives:
- Provide the appropriate quality and quantity of forage for the livestock present.
- Ensure survival of the forage stands, promoting healthy, vigorous plant growth, and maintaining the desired botanical composition.
- Obtain the desired quality of life for the manager
- Protect the environment while conserving natural and nonrenewable resources.
Increasingly, other objectives also must be considered:
- Develop and protect wildlife habitat
- Sequester carbon from the atmosphere
- Reduce soil loss from wind and water erosion
- Protect water quality and quantity, animal health and welfare, animal product quality and safety.
- Protect aesthetic value and open space
- Offer hunting, eco-tourism, or recreational opportunities
In the future, integrating grazing systems with cropping systems may offer one of our best opportunities to manage and protect our natural resources while providing an economic return and maintaining needed levels of food and fibre production to meet the needs of an increasing global population. (Why, this is already happening, particularly with what is called crop-residue grazing or aftermath grazing.)
Grazing Management
Grazing management involves manipulation of the soil-plant-animal complex to achieve the desired results.
Grazing management can be made more intensive or more extensive. Intensive grazing management uses additional inputs of resources, labour, or capital to increase livestock production per acre or per head or to improve forage production and utilization. Extensive grazing management uses lower optimum inputs of labour, resources and capital to achieve profitable and sustainable plant and animal production.
More or less intensive systems are not "good" or "bad." In fact, managers do not simply choose between extensive and intensive systems, they select from a continuum of possible inputs that might include more managerial time, more fertilizer nutrients, more fencing, or other inputs. Choices are influenced by assessment of input costs in relation to the value of the anticipated productivity increases and economic return. The inputs chosen first are often those judged to be most limiting, i.e., those with the greatest likelihood of increasing productivity or efficiency of production. Many weather, soil, plant, animal, and environmental impact considerations must enter into the decision.
Management strategies and intensity of management must also fit the lifestyle goals and abilities of the manager. Systems that demand intense management will not work well in situations where circumstances compete for time and energy required to manage such systems no matter how well suited the system may be in other respects.
Nomenclature of Grazing Systems
The term animal unit(AU) was developed to facilitate comparison of different kinds of livestock. An animal unit is defined as an 1100 lb (500 kg) nonlactating mature cow (Bos taurus) fed at maintenance or its equivalent in other kinds and classes of livestock. Defining the equivalent presents challenges and has been the subject of much debate. An often used general rule of thumb suggests that five ewes (Ovis aries) are equivalent to on mature cow or one horse (Equus cabalus).
A more exact way to equate livestock is on the basis of metabolic body size, generally accepted as the animal's weight in pounds to the 0.75 power (BW0.75). Thus, 1 AU = (1100 lb)0.75=233. An 882-lb animal developed to equal 197, or 0.85 AU (197/233=o.85). This mathematical approach was developed to equate animals based on their body surface area rather than their true body weight. It is based on the assumptions that heat loss is more nearly related to body surface area than to body weight and that, expressed on this basis, heat loss is a constant for all species. Using this formula, comparisons have been made literally from mice to elephants.
Forage mass is the amount of forage dry matter per unit land area at a single point in time. Forage yeild is the total mass of forage produced per unit of land area over a period of time. Forage allowance is a relationship between forage mass per unit area and the number of animal units at any given point in time. At high allowance levels, each animal as a large amount of forage available from which to choose its diet. Performance per animal generally increases as forage allowance is increased up to some point, after which it will level off.
Stocking rate is an animal-to-land relationship measured over a defined time period. Stocking density refers to the animal-to-land relationship at a single point in time. Grazing pressure is a ratio of animal units to forage mass. When grazing pressure is low (i.e., few animal units per unit of forage mass) forage supply exceeds animal needs. Individual animal performance may be high due to selective grazing and/or optimum bite size, but output per unit of land area is decreased because forage is wasted. In this case, increasing grazing pressure may increase output per unit area. However, as grazing pressure continues to increase, performance per animal and per acre will begin to decline.
Grazing Methods
Grazing methods are grazing management procedures designed to achieve specific objectives.They are used to achieve specific defoliation strategies for plants or to allocate nutrition to different classes of livestock. They may influence nutrient recycling or be used to discourage trailing, a social behaviour in which cattle move in single file, forming paths of bare soil that can lead to soil erosion or streambank degradation. There are many grazing methods: rotational and continuous stocking, creep grazing, first-last grazing, sequence grazing, strip grazing, buffer grazing, frontal grazing, and others. No one grazing method is the best. Each is designed to accomplish specific objectives; thus, choosing the correctt method is critical to success. Indeed, several different grazing methods are usually included within a grazing system.
Continuous and Rotational Stocking
Continuous stocking allows livestock unrestricted and uninterrupted access to a specific area for a specific time. No subdivision fences are used during this period. Continuous stocking does not imply season-long use and may in fact be a fairly short period, but it does require intentionally defined period. In response to changes in forage supply during the period of use, the manager can add or remove livestock, increase the total size of the area being grazed, or provide supplemental feed to maintain the desired forage-to-animal level.
Rotatonal stocking implies recurring periods of grazing among two or more paddocks with periods of rest and regrowth for the forage between defoliation events. Grazing periods can be shortened or lengthened to achieve optimum forage management. When forage productivity is high, rotational stocking allows the harvest of some paddocks for hay or silage before they become overly mature. When growth slows and additional forage is needed for grazing, some or all paddocks are reinserted into the rotation. Normally, a paddock is grazed until 70% to 80% of the available forage has been utilized or when remaining dry matter substantially limits intake (500 lb/acre). Forage utilization is usually somewhat lower with continuous stocking, typically stocking, typically 55% to 65%.
Rotational stocking is particularly useful for forage species that benefit from rest periods. For instance, most alfalfa cultivars persist better and yield more with about 4 weeks between grazing cycles due to their cyclical use and replenishment of root and crown nonstructural carbohydrates. Alfalfa is generally sensitive to defoliation periods that extend into this carbohydrate replenishment phase, which normally begins after shoots reach a height of about 6 inches. Grazed continuously, alfalfa plants can be weakened, become less competitive with grasses, or even die. However, grazing-tolerant alfalfa cultivars perform better under continuous stocking than traditional alfalfa cultivars.
During other times of the year, continuous stocking may be preferable for alfalfa. If autumn temperatures are sufficienctly cold to prevent alfalfa regrowth, forage that accumulated during late summer and early autumn can be stocked continuously without harming the alfalfa. Giving animals access to the entire pasture at this allows selective grazing of alfalfa before freezing damage causes excessive leaf and quality losses.
Buffer Grazing
Pasture supply is not constant throughout the year due to growth habit and environmental effects. One approach for adjusting forage supply with continuous stocking is to use temporary electric fencing to exclude livestock from part of the area, which can be harvested later if it is not needed for grazing.
Closing off a variable area gives the flexibility to accomodate low production in a case of drought, high production, or changing animal demand. As the season progresses, the temporary fence is moved forward or backward to adjust the amount of forage available for grazing.
Strip Grazing
Strip grazing confines animals to an area to be grazed in a relatively short period. Stocking density is high enough to utilize the available forage quickly, usually in 0.5 to 7.0 days. This grazing method is particularly applicable to forage crops where no growth is expected during grazing. Utilization is high with this grazing method, up to 80% to 90%, because grazing takes place quickly on a small portion of the total area, reducing waste due to trampling and fouling.
Strip grazing should not be confused with rotational stocking. Strip grazing is a method of allocating forage and does not imply rest, recovery, and reuse of the area.
Creep Grazing
Nutritional needs of livestock differ among production stages and animal objectives. Beef cows need high nutrition in late gestation, during breeding, and during the first 4 months of lactation. In contrast, the nutritional needs of ewes increase 6 to 8 weeks before lambing but needs for peak lactation occur just after lambing. Nutritional level of ewes should be increased again prior to breeding to improve conception races.
Nutrient intake and milk production by the cow or ewe during early lactation is very important to the offspring, but as milk production declines, nutrient requirements also decline. On the other hand, the nutrient requirements of the offspring are increasing during this time. Research has demonstated that feeding the cow or ewe above nutrient requirements does not improve performance of the offspring. Only about 65% of the potential weight of calves weaned at 8 months of age is attributable to milk production by the cow. Research in Virginia demonstrated that daily gains of calves increased by 80% when they were creep fed in addition to milk compared with calves that had milk only. Feeding cows to gain during this period did not improve calf performance.
Creep grazing partitions feed nutrients between the dam and its offspring by allowing calves to graze areas from which cows are restricted. The calves can selectively graze highly palatable and digestible plant parts to optimize intake and increase gains. Cows graze an area that, while providing adequate quality and quantity to meet their lower nutritional needs, forces them to utilize a higher percentage of forage dry matter. BEcause an ample supply of high-quality creep forage is provided directly to the calf, cows can be forced to utilize their pasture more completely by consuming lower quality plant growth.
A creep gate with openings large enough to allow offspring to pass through can be placed between the base pasture grazed by dams and the adjoining creep paddocks. To encourage their use, creep grates should be placed in areas frequented by the livestock. The forage species used in the creep area is less important than providing a sufficient quantity of vegetative, leafy, high-quality forage to allow selective grazing and maximum intake.
First-Last Grazing
First-last grazing divides the forage in a paddock into higher- and lower-quality portions by sequentially grazing with two or more groups of animals with different nutritional requirements. First-last grazer groups can even be different livestock species.
Forage quality of most pasture swards is stratified, with the highest-quality forage at the top of the canopy and the lowest-quality forage at the bottom, nearest the soil surface. When introduced into a new paddock, animals also selectively graze the upper portion of the canopy first. Thus, the first grazers, animals with high nutritional requirements, such as lactating dairy cows or finishing lambs or cattle, utilize only the best-quality upper portion of the plant canopy. This maximizes selective grazing and bite size, ensuring these animals both the highest quality and intake-potential forage. This group moves forward to the next paddock before their nutrient intake becomes restricted.
The last grazers are then brought in to graze forage left behind by group one. Last grazers should be animals with lower nutritional requirements, such as dry cows or cows in late lactation. The lower dry matter intake and nutrient requirements allow these animals to perform adequately in spite of the reduced quality and quantity of the remaining forage.
Mixed Grazing
Mixed grazing combines two or more animal species in the same grazing system. The animal species may graze the area together or separately, at different times. Mixed grazing can be useful in altering parasite cycles. Increasing the period when a particular species is off the pasture helps because parasite eggs gradually die over time. Rejection of forage due to fouling with dung and urine is also reduced in mixed grazing systems because animals are less prone to reject forage fouled by another species. Mixed grazing also takes advantage of differing animal preferences for forage species, canopy heights, and chemical composition characteristics. Goats, for example, prefer to browse which helps control woody and other weed species that are rejected by cattle. Instead of representing a weed control cost, mixed grazing controls those weedy plants while using them in livestock production.
Sequence Grazing
In sequence grazing, two or more land units differing in forage species and composition are used in succession. Each unit can be subdivided for rotational stocking or they can be grazed contrinuously. This may help in matching forage quality and quantity with livestock needs. In a grazing system based on monocultures or a single mixture, all paddocks would have the same response to environmental stresses.
Different forage species or mixtures may have peak production at different times or may be more heat or drought tolerant, and thus improve the seasonal distribution of production compared with a single species. Cool-season and warm-season forage species have different temperature optima for growth, and, thus, provide forage at different times of the year.
Frontal Grazing
Frontal grazing takes advantage of animal behaviour. This method uses a sliding fence moved by the livestock as they push to gain access to ungrazed forage. Grazing efficiency can be high due to uniform use and less trampling of ungrazed forage. Manure is more evenly distributed as livestock advance across a field.
For frontal grazing to work well, a relatively flat pasture free of trees and topographical features that would impede forward movement of the fence is needed. When appropriate, frontal grazing may increase grazing days per acre due to efficiency of forage use, but it does not normally increase individual animal performance compared with either continuous or rotational stocking.
Stockpiling
Stockpiling is a forage management technique by which forage produced during a period of higher production is allowed to accumulate to be grazed later, when growth rates are lower. Some forages lend themselves better to this management than others.
Tall fescue is well suited to this management strategy and is commonly hayed or grazed in early August and about 60 lb of N/acre are applied. Livestock are excluded while the tall fescue grows during late summer and autumn. During this period, temperatures are declining but conditions are usually favorable for forage growth. Nitrogen encourages growth and leaf production, whcih promotes photosynthesis. Lower temperatures slow respiration more than photosynthesis, so nonstructural carbohydrates accumulate.
By early November, there is typically about 1 to 2 tons/acre of high-quality fescue forage available for grazing. Leaves of tall fescue, at vegetative stage in fall, can often be 2 to 3 ft long. On average, 1 acre of stockpiled fescue and about twenty 50-lb bales of moderate-quality hay will provide the feed nutrients need to maintain one beef cow through the winter. With freezing and thawing in late winter, quality of the stockpiled tall fescue will decline, and it may be desirable to have some good-quality hay to supplement livestock even when forage is still available for grazing, particularly if cows are calving during late winter.
Warm-season grasses can also be stockpiled for winter grazing and their potential should not be overlooked. Examples include bermudagrass, old world bluestem, switchgrass, or forage sorghums. Qualtiy is usually lower than for cool-season grasses. Warm season grasses become dormant during autumn and do not accumulate nonstructural carbohydrates. Phosphorus and sulfur are particularly likely to be deficient for animal needs when warm-season grasses are stockpiled.
Considerations in Developing Grazing Seasons
The ability of a grazing animal to ingest needing nutrients is influenced by animal factors, chemical and phyical attributes of the plants, sward characteristics, environment, and management. Many factors affect nutritive value of the forage. In general, legumes such as clovers and alfalfa and cool-season annual grasses, including annual ryegrass and the small grains wheat, oats, barley, and rye, are highest in quality. Cool-season perennials such as orchardgrass and smooth bromegrass rank second, while warm-season perennials, including bermudagrass and old world bluestems, are lower in nutritive value. There are many exceptions, however. Growth stage, canopy morphology, environmental conditions, and other factors greatly influence forage quality and animal performance.
Nutrient requirements vary among different kinds and classes of livestock. The highest-quality forages are generally most appropriate for lactating dairy cows, finishing cattle or sheep, preweaned calves, lambs, or foals, and animals at hard work. Breeding stock and growing animals have a more moderate nutrient requirement, while mature, nonworking or producing animals and dry cows or ewes have the lowest nutrient requirements to simply maintain these animals.
A key goal of any grazing system is to match forage quantity and quality with animal requirements. Seasonal dairying, for example, is based on late winter calving to match early lactation of cows with the high quality and quantity of forage normally available during spring in humid temperate regions. By the time forage quality and growth rates decline later in the season, peak lactation has passed and nutrient demand by cows is lower. Cows are dry and have lower forage quality and quantity requirements during winter when grazing is scarce.
Systems should be designed to minimize supplemental feed needs, but almost all systems will require some supplementation during periods of low forage growth. This could be forage harvested previously during times when forage growth rate exceeds livestock demands. Crop residues such as corn or grain sorghum stalks; co-products from other industries, such as stems, leaves, and burrs removed during the ginning process for cotton ("gin trash"); distillers' grains; or other plant and animal industry co-products can provide valuable supplemental feed for livestock as well.
Grazing system design must consider fixed factors such as climate, amount and distribution of precitipation, the soil types, and perhaps the capital available to invest. Other factors, such as forage species, soil fertility, and soil pH, usually can be modified. Cool-season perennial forages for the basis of grazing systems in much of the northeastern US, while warm-season perennials should for the basis of systems in the southeastern US and throughout much of the West. Warm-season forages may complement a cool-season base or cool-season forages may extend grazing for a system based on warm-season perennials.
Grazing systems should be easy to manage and have sufficient flexibility to accomodate varying environmental, market, and production conditions. There are many ways to build flexibility into systems. Buying and selling animals may offer opportunities to match forage demand with forage growth. Stored or stockpiled forages buffer against times of low forage growth.
Successful systems should do the following;
- Maximize grazing days.
- Minimize requirements for stored feeds and supplements.
- Closely match nutritional needs of livestock with potential for growth and quality of forage.
- Use grazing management to minimize needs for pest control.
- Conserve excess forage for hay, silage, or stockpiled grazing.
- Allocate nutrition to meet the varying nutritional needs of livestock.
- Provide for flexibility.
- Use plants (primarily perennials) and animals that are adapted to local conditions.
- Recycle nutrients effectively and safely.
- Be practical and profitable to manage.
Widely used livestock fences include high tensile wire (electrified or not electrified), barbed wire, electrified tape or wire, various types of woven wire, and specialized types such as board or stone fences. They differ widely in initial cost and maintenance requirements. The best choice depends on the economics, availability of materials, durability requirements, and specific safety concerns, and the ability of the fence type fo accomplish its specific purpose.
Barbed wire is generally avoided for horse pastures because the aggressive, nervous behaviour of horses can result in fence-related injuries and because some horses have high individual animal value. Electric fences are less effective for sheep because their wool provides a natural insulation, but these fences can help to control predators such as coyotes. Fences are less expensive and should be minimized. Less fencing material is needed to surround a square or circle than other shapes with the same unit land area enclosed. The system and the landscape should dictate the needs for fencing, and the system should be designed before the fences are built.
Nutrient Management Considerations
Grazing animals remove in their bodies or in animal products, such as milk, only a small proportion of the N and minerals contained in ingested forage. For example, a 650-lb steer contains only about 5 lb of P. In contrast, a 5-ton per acre yield of alfalfa hay that averages 20% crude protein and 0.3% P will remove 320 lb/acre of N and 30 lb/acre of P. Nutrient export may be desirable to remove excessive nutrients. Conversely, pastures require far less fertilizer inputs to maintain fertility than do areas where hay or silage is produced.
Most of the nutrients consumed by grazing animals are excreted in urine and feces. Woodmansee found that 83% of the N in forage grazed by steers was returned, excreted in urine and feces. Most urinary N is readily available to plants, while feces N is primarily in organic forms that must be mineralized by microorganizms before becoming available for plant uptake. About 30% to 50% of the N voided by grazing animals is volatized and lost to the atmosphere as ammonia. Phosphorus is excreted mostly in the feces. The value of waste nutrients from grazing livestock for forage growth is reduced by their typically uneven distribution over the pasture surface. Factors including landscape features, position of and distance traveled to water, and grazing system design can influence distribution patterns of manure and urine.
Nitrogen and P are currently the nutrients of primary concern in environmental pollution. Application of large amounts of animal wastes from confinement feeding have increased concerns about excessive levels of soil P in recent years. Phosphorus is relatively immobile in soils and accumulates to levels well above the needs of plants or animals. Excessive soil P contributes to pollution of surface waters primarily through direct movement with eroded soil particles.
Nitrogen follows many different pathways through the soil-plant-animal sysytem and is subjected to losses through leaching, volatilization, denitrification, and erosion. Once in the soil, other forms of N can be quickly converted to nitrate, which is highly water soluble. Leaching of nitrate into water presents health hazards and volatilized N forms can contribute to air pollution and odor problems. Nitrous oxide, produced during denitrification, is a greenhouse gas and contributes to ozone depletion. Nitrate con also accumulate in plant tissues when soil levels are high. Nitrate in excess of 0.25% in forage raises concerns for animal health, and levels above 0.5% should be considered potentially toxic. Including legumes with grasses contributes N and decreases or eliminates the need for N fertilizer, but it does not necessarily prevent nitrate leaching primarily due to recycling of N through the grazing animal.
Livestock Water Considerations
Although livestock obtain some water from snow, dew, and moisture in forages, an adequate suppy of good quality water is essential to maintain animal health performance, and feed intake. Animals consuming green, succulent forage have decreased water consumption, while dry feeds and high salt or protein intake increase water consumption. Water consumption increases as temperatures increase. For example, a 900-lb lactating cow consume about 11.4 gallons of water per day when the temperature is about 40 F. Daily water consumption increase about 16.2 gallons/day when temperatures rise to about 90 F. Cattle grazing in steep, rough terrain should not have to travel more than 0.5 mile per day to obtain water, while those on level or rolling land should not have to travel more than 1 mile. Giving livestock direct access to streams, ponds, and other waters sources can kill bank and border areas (riparian) vegetation, push soil into the stream, and contribute to water pollution.
Designing Forage/Livestock Systems
A good place to begin designing forage/livestock systems is to evaluate land resources and the climate. These are features that cannot be altered easily. Next, assess what forages are best suited to these conditions: First, in general terms, whether the system should be based on cool-season or warm-season forages and the extent to which the base can be complemented with less well suited forages that could help fill feed gaps. Then, in terms of specific forage specie that might be used. What are the livestock requirements and when will peak feed needs occur? To what extent can the period of maximum feed requirement be matched with the time of greatest forage supply? How will periods of forage deficits be filled?
In regards to systems for different animal species besides cattle, these same principles can still be applied in designing the right forage/livestock systems for you. A key factor is to understand the nutritional need, behaviour, and production goals for the animals and to understand why and which forages are adapted, when they offer opportunities for use, and how they must be managed. Then--put these together.
