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Forage and Pasture
Forage Management Guides
Self-Study Guide 1: Developing an Overall Forage Plan

Profitable grassland management for livestock pasture depends upon matching forage growth with livestock nutritional needs. Every livestock producer must first be a "grass farmer" since ruminant livestock depend directly on the quality and quantity of forage available. Shortages of forage quality or quantity during critical periods of the animal's productive cycle results in loss of livestock production. This lesson will discuss principles that can be used to develop an overall pasture plan that matches forage growth with animal nutritional needs.

To match seasonal animal requirements with seasonal forage growth requires planning. The following questions can be used as a guide in developing a forage plan on any farm:

• When do the animals have the highest nutritional requirement?
  
• How much forage do the animals eat?
  
• How much forage is needed during the year?
  
• What are the seasonal forage production patterns?
  
  

When Do Livestock Have the Highest Nutritional Requirement?

Cattle nutritional requirements change throughout the year as the animals go through different stages of production. Forage quality must be higher for growing animals than for mature animals. Growing animals, such as steers or heifers, need a constant supply of high quality feed through the season to maintain growth. As an animal matures its nutritional needs change. The forage quality and quantity needed by mature animals also changes with production stage (pregnancy, lactation, etc.) through the year.

A mature beef cow goes through four stages of production each year (Figure 1). These stages are calving and rebreeding, mid-lactation, mid-gestation, and pre-calving. Nutritional needs of breeding animals are different during each of these stages.

The calving and rebreeding stage lasts 90 days. Nutritional needs of the cow are the highest during this stage as the cow goes through peak lactation and rebreeding. Lack of nutrition during this period can result in lower milk production, reduced weaning weights, and failure to re-breed on schedule to stay on a twelve-month calving cycle.

The mid-lactation stage usually lasts 115 days. During this stage the cow is pregnant and lactating. As the calf grows the cow’s nutritional needs will drop throughout this stage.

The mid-gestation stage lasts about 100 days. Calves are weaned at the beginning of this stage. Nutritional needs of the dry cow are at the lowest point because she only has to maintain herself and the developing fetus.

The pre-calving stage begins about 60 days before calving and is a very important period nutritionally. Most of fetal development is occurring and the cow should be gaining weight. Inadequate nutrition during this stage can cause weak calves and poor rebreeding success.

Figure 1. Changes in TDN requirements by stage of production (Spring-calving, 1,100-lb. beef cow with average milk production)

First or second calf heifers need higher quality forage than mature cows during all four of these stages since their bodies are still growing plus they are producing a calf. Mature bulls also need good quality feed during the breeding season but can get by on lower quality forages other times of the year.

How Much Forage Do the Animals Eat?

Although cattle need certain forage quality at specific stages of production, they also need adequate quantity. Forage requirements vary not only with the animal's stage of production, but also by body size. Large animals need more feed to maintain themselves than do smaller animals. The following table gives guidelines for estimating forage Dry Matter Intake (DMI) for certain classes of animals. These figures are given as a percent of body weight (BW) to account for the difference in forage requirement due to body size.

Table 1. Approximate daily forage DMI requirements for different classes of cattle

Calculating Forage Dry Matter Intake Requirements

The following examples illustrate how to calculate forage DMI requirements.

Example: Calculate the daily forage dry matter needs of this herd during the spring grazing period:

Spring-Calving Beef Herd

30 cows - lactating (avg. milk prod.) with an avg. weight =1,100 lbs.

1 bull - 2,000 lbs.

10 heifers - avg. weight = 750 lbs.

Solution: Calculate the total weight of animals in each productive class.

Next find the percentage of body weight (BW) that the animals in each class will consume on a daily basis. These cows are lactating and are average milk producers so their dry matter requirement is 2.5 percent of their BW per day. During the breeding season, the bull needs 2.5 percent of BW. The growing heifers need 3 percent of BW per day. The dry matter intake for each class of animal is as follows:

Example: Calculate the daily forage dry matter requirement for the same spring-calving herd for the fall grazing period when the cows are dry in mid-gestation.

Solution: Since the cows are dry, their dry matter requirements are 2.0 percent compared to 2.5 percent when they were lactating. The growing heifers need 3 percent of their BW per day. The breeding season is over so the bull’s requirements can be calculated at 2 percent. The same animal weights are used to simplify the example.

How Much Forage is Needed During the Year?

Calculating Actual Forage Availability Required for Different Grazing Management Systems

To determine if forage availability is adequate for the herd, you must also consider the harvest efficiency of the grazing system. No harvest system is 100 percent efficient, especially grazing animals. In a pasture system, estimated animal utilization of the forage is between 30 and 65 percent of what is actually grown. In continuous grazing systems cattle are allowed to continually graze a pasture with no restrictions on rotation. Much of what is produced is wasted. It is estimated that only 30 to 35 percent of the total forage produced is actually eaten by the livestock. The other 65 to 70 percent is trampled, soiled by mud, manure, and urine, or used as bedding areas.

As grazing management restricts the grazing habits of the animals, a higher percentage of the forage is consumed. When well managed rotational grazing or management-intensive grazing (M-IG) is used, forage utilization can be as high as 65 to 70 percent of the forage produced. This level of utilization can only be achieved by frequently rotating animals among several pastures or paddocks.

Example: (use the spring grazing example shown previously) Calculate the actual daily amount of forage DM needed for this herd for continuous and management-intensive grazing systems.

Solution: The daily dry matter intake was calculated to be 1,100 lbs. during the spring grazing period. Forage utilization in the continuous grazing pasture management system is only about 35 percent. This means that the amount of forage dry matter available needs to be almost three times the amount the herd will actually eat per day.

1,100 lbs. DMI per day ÷ 0.35 = 3,142 lbs. forage DM needed per day

In a properly managed rotational grazing system, forage utilization is about 65 percent, so actual forage DM needed is only about 1.5 times as much as what is actually consumed.

1,100 lbs. DMI per day ÷ 0.65 = 1,692 lbs. of forage DM needed per day

Calculating Forage Dry Matter Requirements for a Specific Season

A reasonable goal is to have pasture available about 300 days per year and to only feed hay for about two months. To simplify forage planning, the grazing season can be divided into three 100-day periods representing spring, summer, and fall. These periods roughly match the seasonal production stages of a beef cow already discussed as well as the seasonal growth periods of cool- and warm-season forages.

The following example gives a guideline for calculating the actual amount of forage dry matter production needed in a pasture to carry the same herd during the spring season.

(Lbs. dry matter needed per day) x (number of days in season)

Example: What is the forage DMI requirement for this same spring-calving herd during the spring (100 days)?

Solution: The total daily forage DMI need was calculated to be 3,142 lbs. for continuous grazing and 1,692 lbs. for management-intensive grazing so the amount of forage production needed for the spring season for this herd is:

Continuous Grazing

3,142 lbs. per day x 100 days = 314,200 lbs. forage DMI needed for spring season.

Management-Intensive Grazing

1,692 lbs. per day x 100 days = 169,200 lbs. forage DMI needed for spring season.

Estimating Hay Supplies

Hay supplies cannot be estimated directly from the percentages given for DMI due to several factors. Storage and feeding losses of hay can range from as low as 5 percent to as much as 50 percent depending on conditions and hay type. Dry hay also contains 10 to 15 percent moisture that is not accounted for in the DMI calculation. A hay supply can be estimated by adding a moisture factor and a waste factor to the DMI amount calculated for a particular animal.

For example, if the DMI of a 1,000 lb. cow was calculated to be 25 lbs., the moisture content of the hay was 15 percent, and the waste factor was estimated at 25 percent then the daily amount of hay needed would be 35 lbs. or 40 percent more than the DMI intake requirement (25 x 1.4 = 35). This would amount to slightly more than 1 ton of hay for a 60-day feeding period or 1.5 tons of hay for a 90-day feeding period. The amount of hay needed depends directly on the waste factor for a particular storage and feeding system.

What are the Seasonal Forage Production Patterns?

No single forage provides adequate year-round grazing, but complimentary combinations of several forages can provide good quality season-long grazing and some winter grazing as well. Any forage selected for improving a pasture program should be adapted to the soil, the growing conditions, and the level of management available on a particular farm. A balanced pasture program should include both cool-season and warm-season forages (Figure 2) although the recommended amount of each type will vary with location in Arkansas. In north Arkansas a pasture program should include approximately one-half to two-thirds cool-season forages and one-third to one-half warm-season forages. These ratios are reversed in south Arkansas to be one-half to two-thirds warm-season forages and one third to one-half cool-season forages due to the warmer climate.

A forage program can be primarily perennial forages but can include annual forages depending upon growing conditions and forage demand. Perennial forages can be grouped into three broad categories - cool-season grasses, warm-season grasses, and legumes.

Cool-Season Grasses

Cool season grasses grow best during spring and fall, but are usually dormant or unproductive during hot summer months (Figure 2). Perennial cool season grasses adapted to Arkansas include Kentucky bluegrass, orchardgrass, perennial ryegrass, reed canarygrass, smooth bromegrass, and tall fescue. These grasses are commonly grown in pure stands, in mixtures with other cool season grasses, or in combination with legumes.

About two-thirds of the annual growth of cool season grasses occurs in the spring and about one-third of the annual growth occurs during the fall (Figure 2). Forage quality of cool-season grasses is very high when new growth begins in spring, but declines as the plants become mature and produce seed. Forage quality of fall regrowth of cool season grasses is also very good, but it does not decline during the fall growth phase as in spring because plants remain vegetative during that time of year. Cold weather, snow, or ice can cause forage quality to decline during winter.

Figure 2. Complementary growth patterns of cool- and warm-season grasses

Tall fescue is the major perennial cool season grass in Arkansas. Besides providing forage in spring and fall, tall fescue can be managed for winter pasture. Fall growth of the tall fescue is allowed to accumulate or stockpile beginning in August or September and grazing is deferred until winter. Forage residue remaining from the spring or summer is lower quality and should be removed from the field by grazing or haying before the fall growth begins. Stockpiling the fall growth works well because the accumulated growth tends to remain high in nutritive quality and does not become mature as it does in spring. Tall fescue foliage tolerates freezing weather better than most other cool season grasses so it is preferred for fall stockpiled pasture.

Many tall fescue pastures are infected with the fescue endophyte which causes fescue toxicosis in grazing animals. Animals grazing fescue pastures that are infected with the endophytic fungus can show symptoms of lameness, heat stress, lower weight gains, low milk production, and low conception rates. These symptoms are often more severe when cattle are grazing infected fescue during hot weather. The negative effects of the fescue endophyte can often be offset by reducing nitrogen fertilizer rates, by planting new pastures of endophyte free fescue varieties, by incorporating legumes into existing infected pastures, and by using other forages during the hot summer months.

Warm-Season Grasses

Warm-season grasses grow best during the summer months but grow very little in spring or fall (Figure 2). Warm-season grasses provide good quality, actively growing forage during the hot summer when cool-season grasses and many legumes are dormant or unproductive. A forage program that includes both warm-season and cool-season grass pastures will provide a more constant forage supply over the growing season.

Native warm-season grasses include big bluestem, indiangrass, little bluestem, and switchgrass. These grasses are usually grown in pure stands or in mixtures with other warm-season grasses. They are usually not grown in combination with most introduced legumes or cool-season grasses because the native warm-season grasses are not as aggressive as many legumes or cool season grasses especially in fertilized pastures. The native grasses should not be grazed shorter than eight inches to maintain vigor and regrowth of the plants. Introduced or non-native warm-season grasses include bahiagrass, bermudagrass and Caucasian bluestem. Caucasian bluestem and bermudagrass are normally grown in pure stands because they are more aggressive forage plants, they are lower growing than the native warm-season grasses, and they must be grazed at much shorter heights than the native grasses in order to maintain forage quality. All of these species are perennials.

The native warm-season grasses respond to moderate fertilizer applications and are much more desirable for wildlife cover than introduced warm-season grasses or most cool-season grasses. Introduced warm-season grasses such as bermudagrass and Caucasian bluestem respond well to high rates of nitrogen fertilizer, but have little value as wildlife cover.

Warm-season grasses should be grazed when they are in the vegetative stage of growth. Fiber levels increase rapidly as the plants mature, reducing forage quality and making warm-season grasses undesirable for stockpiling for later grazing. These grasses usually have a very rapid growth rate and very high production potential. Close attention is required to prevent them from becoming too mature for good forage quality.

Legumes

Legumes include alfalfa, annual lespedeza (Kobe or Korean), arrowleaf clover, birdsfoot trefoil, crimson clover, red clover, and white or ladino clover. Red and white clovers grow in spring, early summer, and fall. Alfalfa and birdsfoot trefoil grow from spring through fall. Annual lespedeza is a summer annual legume that germinates in spring, grows in summer, and dies at frost. Arrowleaf and crimson clover are winter annual clovers that germinate in fall produce most of their growth in spring, then die during summer.

Legumes are commonly grown in combination with grasses to improve nutritional quality of the pasture. Legumes are highly palatable and nutritious to livestock and generally have higher nutritive quality at any given growth stage than grasses. Grass/legume pastures containing at least 25 percent legumes show little response to nitrogen fertilization because the nitrogen supplied by the legume through nitrogen fixation is high enough to support the growth of both the grass and legume. Legumes need higher soil pH levels than grasses for optimum persistence and growth.

Legumes can be used for pasture in spring, summer or fall, but require careful management to maintain adequate stands. Legumes also help offset the effects of fescue toxicosis when mixed in fields of endophyte infected tall fescue.

How Forage Plants Grow

Leaf growth of perennial forage grasses begins in growing points or buds in the crown of the plant. The buds produce tillers and leaves grow from the tillers. Leaf growth is fueled by photosynthesis after the leaves are large enough to capture adequate sunlight. Cool-season grasses such as tall fescue keep the growing points low near the soil surface so they are protected from close grazing. Regrowth after grazing usually comes from the elongation of existing leaves rather than initiation of new tillers from crown buds. Other grasses like bermudagrass also maintain growing points close to the soil surface and can tolerate close grazing.

Tall native warm-season grasses also begin growth from basal crown buds, but as the plants grow the growing point becomes elevated above the soil surface where it is susceptible to grazing. Native warm-season grasses cannot be grazed as short as most cool-season grasses because of the elevated growing point. When the growing point is removed by close grazing or in closely mowed hay operations, all regrowth must come from secondary crown buds. Production of a new tiller from crown buds requires a great amount of energy and is much slower than regrowth from leave elongation. The plants can become weakened and the stand is open for invasion of weeds. Native warm-season grasses must be rotationally grazed and should not be grazed shorter than six inches to protect the growing points.

Top growth of perennial legumes begins with shoots arising from crown buds. After the shoots are large enough to capture adequate sunlight for photosynthesis, the growth of the shoots comes from growing points located in the terminal bud at the top of the plant and from growing points located at the tips of branches. Most of the growth of a legume comes from the terminal bud. When the terminal bud or growing point is removed by grazing, all other regrowth must come from the growing points on the branches. As long as adequate leaf area is present the regrowth will be fueled by photosynthesis. Under heavy grazing pressure where all of the topgrowth is removed, any regrowth must be initiated from buds located in the crown of the plant. Regrowth from crown buds is fueled by stored carbohydrates in the roots. If the plants are defoliated too frequently by grazing or haying, the stored carbohydrates for regrowth become depleted and the plants die. Well managed rotational grazing can greatly improve legume persistence in pastures because the plants have time to store root reserves for regrowth. Perennial legumes such as red clover and alfalfa can store large amounts of root carbohydrates and are desirable for hay as well as pasture.

Annual legumes do not have the regrowth potential as in perennials. Annual legumes such as Korean or Marion lespedeza do not build up stored root carbohydrates. When the terminal bud in annual lespedeza is grazed all regrowth must come from side branches since the plant does not have crown buds. If lespedeza is grazed too closely the side branches tend to grow parallel to the soil surface instead of upright. This prostrate regrowth by short lespedeza plants is often too low for cattle to graze even though the growth of the side branches can be significant.

Keep in mind that overgrazing will weaken all forage plants. All of the energy of a plant comes from the sun through photosynthesis. Plants that are defoliated too frequently do not have enough leaf area for adequate photosynthesis and become weak and unproductive or die and disappear from the pasture.

Forage Growth Stages

The growth stage of the forage is very important in pasture management. Forages should be grazed before they reach maturity since nutritive quality is highest when the forage is vegetative and growing. This stage also corresponds with low plant fiber and high digestibility. As the forage matures the nutritional value and palatability to grazing animals decline rapidly. Fiber levels increase as the plants mature decreasing digestibility of the forage.

Plants go through specific developmental stages as they mature. For grasses these stages are vegetative, boot, heading, bloom, and mature seed. Most cool season grasses produce seed only in the spring. Regrowth of cool-season grasses in summer and fall, after the seed stems have been removed by grazing or hay harvest, is vegetative and leafy with no seedheads. Most warm season grasses can produce seed more than once per year. Legumes go through similar stages of development as the grasses. These stages for legumes are vegetative, bud, bloom, mature seed. Legumes, except for annual lespedeza, can flower and produce seed several times during the growing season.

Effects of Grazing Pressure

Grazing pressure or the intensity and frequency of grazing can strongly influence the regrowth vigor of a pasture. Pastures that are grazed too frequently lose plant vigor. Any stress on the plants also limits livestock production because the grazing animals are dependent on the forage. An assessment of the grazing pressure on a pasture can tell about the relative vigor of a pasture. The most common conditions that occur in pastures include over-grazing, spot-grazing, even-grazing, and under-grazing. All of these conditions can occur within the same pasture if animal stocking rate is not properly matched with pasture size and forage growing conditions.

Over-grazed: Over-grazing occurs when the pasture is grazed too frequently without allowing the plants to produce adequate regrowth. Overgrazing and closely grazing are not necessarily synonymous. Pastures plants that are closely grazed can recover and grow normally as long as adequate time is allowed before that pasture is grazed again. Overgrazing does not allow enough time for plants to store nutrient reserves for regrowth before they are grazed again. This results in a depletion of the plant’s nutrient reserves causing slower regrowth and lower plant vigor. Overgrazing also leads to the weakening of the plant’s root systems causing over-grazed plants to respond more slowly to good management practices than properly grazed forages. Overgrazing can shift the composition of a pasture from taller growing forages that do not tolerate frequent grazing to lower growing species that tolerate heavier grazing.

Characteristics of over-grazed fields may include thin stands, very short forage plants, low forage vigor, and invading weeds or brush. Forage plants in over-grazed fields appear uniformly short and weak.

Spot-grazed: Spot-grazing is actually a form of over-grazing in which spots or patches of a pasture are grazed too frequently. Spot-grazing occurs during periods of active forage growth when livestock graze spots in a pasture while allowing other areas of the field to become mature and unpalatable. The regrowth of the grazed forage in the spots is often more palatable than the ungrazed forage so the grazing animals frequently re-graze new growth of theses spots. Spot-grazed fields have uneven forage heights and the forage in the grazed spots may become weak and thin if cattle remain in the field too long. Spot-grazing often occurs when livestock density or number in a pasture is too low for the current forage conditions. Weed invasion often becomes a problem on heavily spot-grazed fields. More frequent pasture rotation will improve the condition of spot grazed pastures.

Evenly grazed: Evenly grazed pastures, as the description implies, have a generally uniform grazing height, thick stands, good forage vigor, and respond well to good management. These pastures often have a good mix of grasses and/or legumes present. Some spot-grazed areas may be present, but make up less than 10 percent of the field.

Under-grazed: Under-grazed pastures often have large quantities of accumulated growth that has become coarse or mature. These pastures have low nutritive value for livestock, but can be good areas for wildlife, depending upon the forages species present. Heavy shade from taller growing forage species can reduce the density of lower growing plants and legumes in a pasture.

Estimating Available Forage

The amount of forage available will determine the stocking rate and pasture size. The following table is a guide for calculating forage availability.

Table 2. Estimated dry matter availability for several pasture types and stand conditions

Source: 1997 Missouri Grazing Manual

Example: Estimate the pasture size necessary for a herd of fifty lactating 1000-lb. cows for a 3-day rotation on fescue pasture in good condition with nitrogen fertilizer. Assume management-intensive grazing is being used (65 percent forage utilization).

Solution: Table 2 shows that the average dry matter availability for fescue + N in good condition is 400 lbs. per inch per acre. If the forage is 8 inches tall at 400 lbs. per inch then 3200 lbs. of forage DM is available. At 65 percent forage utilization only 2,080 lbs. will be grazed. The herd needs 1,250 lbs. of dry matter per day since the cows are lactating making their daily DMI need 2.5 percent of BW (50 x 1,000 x 0.025 = 1,250). With these assumptions, one acre of pasture will provide enough forage for 1.6 days (2,080 ÷ 1250 = 1.6). Two acres will be required for a 3-day rotation. Close estimates of pasture condition and animal intake are important for realistic values. Conservative estimates of pasture condition will help prevent designing paddocks that are too small.

For more information about forage management, please contact your county Extension office.

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