Strategies for Extending the Grazing Season
Agronomy Facts 41
These strategies can be categorized into two major groups: 1) stockpiling (conserving cool-season forages in late summer for use in the fall and winter), or 2) utilizing forage crops that continue to grow in the fall and early winter.
Not all cool-season species are adapted to stockpiling. Most species reduce their growth in the fall because of shorter day lengths and/or they lose their leaves (quality) after being frosted. Tall fescue and birdsfoot trefoil are two forage species which are suited to stockpile management because they continue to grow in the fall and do not lose leaves as readily as other cool-season species do after frost.
Tall fescue is a deep-rooted, long-lived, sod-forming grass that spreads by short underground stems called rhizomes. It is drought resistant and will maintain itself under rather limited fertility conditions. Animals readily graze tall fescue during the fall, but show some reluctance to graze it during the summer months of July and August. Some of this reduced summer palatability, which results in poor animal performance, is associated with the presence of a fungus in the plant (endophytic). Endophyte-free varieties are now available and are recommended for new seedings. Tall fescue is the best adapted cool-season grass for stockpiling (Table 1).
|----- tons/acrea -----|
|a All grasses received 225 lb N/acre/year.|
Numerous tall fescue varieties are being marketed in Pennsylvania, however, only endophyte-free varieties should be selected when seedings are to be grazed. ‘Johnstone,’ ‘Festorina,’ and ‘Barcel’ tall fescue varieties have performed well in Penn State studies. They are endophyte-free and of high quality.
Tall fescue can be part of a forage program but should not be all of it. Legumes with tall fescue improve animal performance and increase forage production during the summer. Tall fescue will withstand closer grazing and more abuse than most cool-season grasses. But it can be over- grazed to the point that vigor and production are reduced. Don’t graze closer than three or four inches, and allow at least 30 days in mid-summer for the tall fescue to recover.
To stockpile tall fescue, don’t graze it from mid- or late August through mid-October. Cattle and sheep perform less than optimally on it during this period. Fertilize with 50 lb nitrogen/acre and allow the growth to accumulate for use in the fall or winter.
Stockpiling and nitrogen fertilizer allow accumulation of forage, however, this results in low tiller density, increased winter injury, and slow recovery in the spring (Table 2).
|N level||Harvests per yeara||Species|
|Kentucky Bluegrass||Tall Fescue||Orchardgrass||Smooth Broomegrass||Timothy|
|lb/yr||----- % ground cover -----|
|a Three harvests per year simulates a stockpile management system.|
The most important thing to remember is that while stockpiling can provide large quantities of herbage for late fall and early winter grazing, it will also delay recovery in the spring. At modest rates of nitrogen fertilization, stands of tall fescue will not deteriorate as fast as other cool-season grasses under stockpiling.
For more information about tall fescue, refer to Tall Fescue, Penn State Agronomy Facts 28.
Birdsfoot trefoil is a perennial legume adapted to production on poorly drained, low pH soils. It can reseed itself, is resistant to Phytophthora root rot and numerous alfalfa insects, responds well to fertilization, and does not cause bloat in animals. These characteristics have expanded its use in the northern United States and southern Canada where the production of other forage legumes is limited. Birdsfoot trefoil is well suited for stockpiling since it holds its leaves at maturity and after frost, thus maintaining a relatively high level of quality.
About 25 varieties of birdsfoot trefoil are available in the United States and Canada. Birdsfoot trefoil varieties are generally characterized by growth habit into two types, Empire and European. Both types are referred to as “broadleaf” trefoils.
Empire-type birdsfoot trefoils are better adapted for grazing situations than the European types because they have fine stems, prostrate growth, and indeterminate growth habit. The Empire types grow slower during establishment and regrow more slowly following harvest than the European types. ‘Dawn’ and ‘Empire’ are high-yielding, Empire-type varieties that have performed well in Pennsylvania tests.
European-type birdsfoot trefoils are better adapted to hay production because they are more erect, establish faster, and regrow faster after harvest than the Empire type.
To stockpile birdsfoot trefoil, avoid grazing between September 1 and the first killing frost. This period is needed to accumulate root reserves that improve winter survival and growth the following spring. The forage that accumulates during the stockpiling period can be grazed anytime after a killing frost.
Refer to Birdsfoot Trefoil, Penn State Agronomy Facts 20, for more information about production and management of this forage species.
Fall Growing Forage Crops
The growth of some forage species is not as adversely affected by cooler fall weather and shorter day lengths as are many cool-season forages. The species which seem to grow best in the fall are tall fescue, prairie grass, perennial ryegrass, and certain brassica crops. These species can provide a valuable feed supply for extending the grazing season.
Prairie grass is a tall growing perennial grass that is suited to well drained soils with medium to high fertility levels and a pH of 6.0 or greater. It is a type of bromegrass, but is different from smooth bromegrass in that it does not have rhizomes and it produces seed heads in each growth period, especially during the summer. Herbage and immature seedheads of prairie grass are highly palatable. It is an excellent grass for providing forage during droughts and for extending the grazing season well into the fall in Pennsylvania.
Fall harvesting (grazing) improves the winter persistence of prairie grass. It will persist for four to six years in Pennsylvania if properly managed. Forage quality of prairie grass compares well with other cool-season grasses but is more palatable.
‘Matua’ is the only cultivar of prairie grass that is currently sold in the United States. This variety was developed under New Zealand grazing conditions and has been very productive in Pennsylvania. Other prairie grass varieties are being evaluated for persistence and productivity by the USDA-Pasture Laboratory and Penn State; however, none of these varieties is marketed commercially in Pennsylvania at this time.
Prairie grass is an ideal grass for grazing systems because of its potential for earlier spring grazing and its fall growth can effectively extend the grazing season by as much as two months over traditional cool-season grass species. Fall yields of nearly 3.5 tons/acre are possible. In addition, because seed heads are palatable, it is not necessary to mow them to maintain animal intake as may be needed with other grasses. Yields of nearly 7 tons/acre have been achieved when harvesting prairie grass for silage.
Prairie grass should not be cut or grazed below a 3-inch stubble height because regrowth energy reserves and buds for plant regrowth are contained in this portion of the plant.
In established prairie grass stands, delaying the first spring grazing will reduce recovery rate and lower the yield potential of the next cutting. Under normal weather conditions, about 25 to 30 days of regrowth is sufficient between harvests. This period is a good balance between yield and quality of prairie grass. Generally, during this time, new shoots have developed at the base of the plant and harvesting or grazing will allow more light to reach the shoots and to stimulate their growth. An approximate 50-day growth period in mid-summer will allow the prairie grass seed heads to mature and drop seed during August which, in turn, will thicken the stand the following year.
Prairie grass persists best when managed so that monthly harvests are made during the fall; spring yield and shoot density increase when multiple harvests are made in the fall. Harvesting only once in the fall (November) has caused 98 percent of the basal shoots (source for growth the following spring) to winter kill. However, when prairie grass was harvested or grazed three times during the fall only 35 percent of the basal shoots were winter killed. Compromise is needed with regard to fall harvesting because late fall grazing reduces slightly prairie grass vigor the following spring and restricts early spring grazing.
Adequate nitrogen fertilization is essential for maximizing prairie grass growth in the fall. Nitrogen applications of 50 lb/acre are recommended after each harvest and in early fall.
For more information about the production and management of prairie grass, refer to Prairie Grass, Penn State Agronomy Facts 39.
Brassicas are annual crops which continue to grow during the fall and into the winter. They are highly productive and digestible and contain relatively high levels of crude protein. They can be grazed 80 to 150 days after seeding, depending on the species and weather (Table 3). In addition, some varieties lend themselves to stockpiling.
|Crop||Plant part consumed||Seeding to harvest
|Regrows after harvest||Seeding rate
|aAn exception is the stemless variety ‘Premier’ which is ready for harvest 80 to 90 days after seeding and will regrow after harvest if not grazed below three to four inches.|
|Kale||herbage||150 to 180a||noa||3.5 to 4|
|Rape||herbage||80 to 90||yes||3.5 to 4|
|Swede||herbage and root||150 to 180||no||1.5 to 2|
|Turnip||herbage and root||80 to 90||yes||1.5 to 2|
Species and Varieties
Several brassica species can provide forage for grazing during the fall. These include:
Kale—The stemless variety ‘Premier’ has consistently survived winters in central Pennsylvania, whereas other varieties of kale usually have winter-killed in December.
Rape—Growth of rape slows or ceases at maturity until leaves senesce and die. Varieties differ in the time this occurs. For instance, ‘Rangi’ rape retains its leaves longer than most varieties, which makes it more suitable for stockpiling and winter grazing than other rape varieties.
Swede—The variety ‘Calder’ has been cold hardy in central Pennsylvania and thus ideal for stockpiling for late- fall or early-winter grazing. However, in general, all swede varieties are recommended for late-fall grazing.
Turnip or Turnip Hybrids—Pennsylvania studies have shown that ‘Forage Star’ turnip is more cold tolerant and retains its leaves longer in the fall than other turnip varieties. Turnip can accumulate dry matter in October as fast as field corn does in August. Growing “out of season” (October and November) makes turnip a valuable crop for late fall grazing.
Proper grazing management is important to optimize the true potential of these crops. Strip grazing small areas of brassicas provides the most efficient utilization.
Rape is more easily managed for multiple (generally more than two) grazings than are the other brassica species. Approximately six to ten inches of stubble should remain after the first grazing of rape; this practice promotes rapid regrowth. Regrowth of rape may be grazed at four-week intervals. On the final grazing, the plants should be grazed close to ground level.
When turnips are grazed twice, the first grazing should remove only their tops. Turnip regrowth is initiated at the top of the root, so this part of the plant should not be removed until the second and final grazing. Like rape, regrowth of turnips can be sufficient to graze within four weeks of the first grazing.
Diseases of brassicas are generally not a problem until the plants near maturity. Stockpiling should not be attempted in fields where brassicas have high levels of foliar disease at maturity. Research has shown yield reductions of 40 percent when disease infected brassica crops were stockpiled for 45 days. Generally, ‘Forage Star’ turnip and ‘Rangi’ rape are better suited for stockpiling than other varieties because of lower disease infestation. To reduce club root rot occurrence, brassicas should not be grown on the same field for more than two consecutive years.
Yield and Nutritional Value
Dry matter digestibility at maturity generally exceeds 90 percent for all plant parts except kale stems. Unlike perennial forage crops, the dry matter digestibility of brassicas does not decrease markedly with increasing plant maturity. This characteristic makes them ideal for stockpiling. However, ruminant diets should not contain more than 75 percent brassica forage because the fiber content is too low for maintenance of proper rumen activity. With their high digestibility and low fiber content, brassicas actually should be considered as “concentrates” rather than “forage” in nutritional planning for livestock.
For more information about brassicas, refer to Use of Brassica Crops to Extend the Grazing Season, Penn State Agronomy Facts 33.
The use of winter cereal crops such as wheat, barley, rye, or triticale can provide fall or early winter grazing opportunities. However, certain management practices need to be modified from what is normally done for grain production. When small grains are to be used for grazing, plant them three to four weeks earlier than for grain production. Increase the seeding rate to 3 bu/acre and apply nitrogen at the rate of 40 lb/acre at planting time.
If the small grains are being planted only for pasture (with no subsequent grain harvest), there may be some benefit to mixing small grains species. This has been beneficial in the southeast United States, where small grains pastures are quite common. Mixing species of rye, wheat, barley, or triticale can help extend the grazing period and reduce the tendency for a strong peak growth period in the spring.
With adequate fall moisture, grazing should be available from October through December and then again in early spring. One acre of properly fertilized and managed small grains should support one animal unit (1,000 lb animal) on a limited grazing basis.
Stocking rate and time of grazing will be somewhat determined by the intended use of the crop. If you are planning to take a silage or grain harvest, grazing should only be moderate. Heavy grazing can reduce grain yields. Moderate grazing in the fall will not result in significant silage or grain losses provided that moisture and soil fertility are adequate. In fact, fall pasturing can be beneficial where the small grain was seeded early and has made excessive growth.
Spring grazing may be started when growth resumes. If a grain or silage crop is to be harvested, grazing should be discontinued when the plants start to grow erect, just before jointing (growth stage 6). Small grains plants will be injured by grazing at any time after their growing points are above the ground.
Temporary electric fencing should provide a practical way to manage these pastures. Although small grains can be continuously grazed, a rotational or strip grazing practice may allow a higher carrying capacity (less wastage from trampling).
Small grains pasture is lush, high in protein, and low in fiber during most of the fall grazing period. Crude protein levels normally range from 15 percent to 34 percent of dry matter, making this forage an excellent protein supplement for many classes of livestock.
Animal Health Precautions
Grass tetany can occur when small grains forage is grazed by cows about to calve or those which have recently calved. This usually occurs in the spring. It is recommended that animal diets be supplemented with a mineral mix containing magnesium. Lactating dairy cows that are grazing small grain pasture should receive an additional 1 ounce of magnesium oxide/cow/day.
There is a risk of nitrate poisoning if animals graze rapidly growing and recently fertilized small grains pasture. Avoid this situation by applying nitrogen fertilizer at planting time or well before the intended grazing period.
Although rare, bloat may also be a health risk when animals graze small grains. This most likely will occur when animals are first turned onto pasture in early spring and gorge themselves with the lush forage. Bloat can be prevented by feeding some stored forage just before turning the animals onto the pasture.
Prepared by Marvin H. Hall and Jerry Jung, assistant professor and adjunct professor of agronomy, respectively.