Tall fescue toxicosis is one of the most costly animal disorders facing livestock producers in the eastern U.S. As reported by Georgia researchers in 1977, it is caused by a fungal endophyte. At present, there is no cure for tall fescue toxicosis. There are, however, proven management strategies that can lessen the effect of toxicosis. One strategy is the replacement of toxic tall fescue with cultivars that are endophyte-free or contain beneficial endophytes. Other strategies involve management of toxic tall fescue pastures by interseeding other forages that can dilute the toxins, rotating livestock to non-toxic pastures, supplementing the diet, limiting the rate of nitrogen fertilizer, controlling the seedheads, ammoniating the hay, and in the case of horses, administering medicinal treatments. Nearly all of these management practices are designed to limit the amount of toxin that is ingested in the animal.

Tall fescue (Festuca arundinacea) is among the most common cool-season pasture grasses in the U.S. (Fig. 1) and is grown in many other countries with temperate climates. In the U.S., nearly all tall fescue pastures planted before 1980 are infected with Neotyphodium coenophialum, a microscopic fungus (Fig. 2). This fungus is usually referred to as an endophyte, because it grows inside (“endo”) the plant (“phyte”). Alkaloids produced by the endophytic fungus cause tall fescue toxicosis, a syndrome that costs U.S. livestock producers more than $600 million each year .

This guide describes tall fescue toxicosis as it occurs in ruminant livestock and horses. It highlights initial efforts to solve toxicosis through plant breeding and offers current management recommendations. Recommendations in this guide are based on data from controlled experiments. Because this is a guide and not an exhaustive review, recommendations are supported by one or two representative citations only.

Tall Fescue Toxicosis and Management

Fig. 1. A stand of tall fescue 18-inches high (A) with close-up view of its seedhead (B). (Photos by Robert Kallenbach and Greg Bishop-Hurley.)

Tall Fescue Toxicosis and Management

Fig. 2. The tall fescue endophyte (Neotyphodium coenophialum) in the tiller (shown here) and seed as seen in a microscope. (Tiller photo by Nicholas Hill.)

 

Tall Fescue Toxicosis and Management

Fig. 2. The tall fescue endophyte (Neotyphodium coenophialum) in the tiller and seed (shown here) as seen in a microscope. (Seed photo by Craig Roberts.)

 

Tall Fescue Toxicosis

Tall fescue toxicosis is a syndrome most easily recognized by grotesque symptoms, such as fescue foot in cattle  (Fig. 3). Toxicosis is also seen in cattle that fail to shed their winter coats in the summer and display a shaggy, unkept appearance (Fig. 4). Some of the most serious symptoms of tall fescue toxicosis, however, are not visible. These include vasoconstriction (narrowed blood vessels that causes restriction of blood flow), high core body temperature, increased respiration, low heart rate, altered fat metabolism (causing fat necrosis) (Fig. 5), low serum prolactin, agalactia (failure to produce milk), suppression of the immune system, reduced forage intake, and low rate of weight gain. Fescue toxicosis also causes serious reproductive problems, such as low pregnancy rate (Fig. 6), thickened placenta (Fig. 7), retained placenta (Fig. 8), and dystocia (birthing difficulty) (Fig. 9). These latter symptoms are particularly severe in pregnant mares.

Tall Fescue Toxicosis and Management

Fig. 3. Fescue foot in cattle. Toxic tall fescue can restrict blood flow to the extremities which may result in hoof loss, particularly during cold weather. (Photo by George Garner.)

Tall Fescue Toxicosis and Management

Fig. 4. Steers near Mount Vernon, MO suffering from tall fescue toxicosis during July. Note the failure to shed the winter hair coat. (Photo by Greg Bishop-Hurley.)

Tall Fescue Toxicosis and Management

Fig. 5. Fat necrosis in the abdominal cavity of a beef cow. Note that fat masses are constricting the intestine. Scale is in centimeters. (Photo by John Stuedemann.)

Tall Fescue Toxicosis and Management

Fig. 6. Effect of toxic tall fescue on reproduction in beef animals in Kentucky and Alabama . As a rule of thumb, each 10% increase in endophyte infection reduces calving percentage by approximately 5%.

Tall Fescue Toxicosis and Management

Fig. 7. Thickened placenta in horses caused by grazing toxic tall fescue. (Photo by Dee Cross.)

Tall Fescue Toxicosis and Management

Fig. 8. A retained placenta in a horse that grazed toxic tall fescue. (Photo by Dee Cross.)

Tall Fescue Toxicosis and Management

Fig. 9. Dystocia, or birthing difficulty, caused by toxic tall fescue. Equines are extremely susceptible to reproductive problems when toxic tall fescue is consumed during late gestation. (Photo by Dee Cross.)

Toxins associated with tall fescue toxicosis.

According to most researchers, toxins responsible for tall fescue toxicosis are ergot alkaloids, a class of compounds produced by the endophyte. Ergot alkaloids include compounds such as clavine alkaloids, lysergic acid amides, and ergopeptines . Ergovaline is the most prevalent and most frequently researched of these alkaloids, although the other alkaloids may also prove to be responsible for tall fescue toxicosis. Ergot alkaloids are highly concentrated in the seed, though they can be measured in the leaf and stem tissue as well . Ergot alkaloid concentrations peak in late spring pastures, when seedheads are present, causing low rate of gain in beef cattle . Alkaloid concentrations decrease during the summer, then increase again in the autumn.

The period of highest concentrations of ergot alkaloids in the pasture does not coincide with visible symptoms of toxicosis in the animal. The reason is that there is a residual effect of ingesting toxic tall fescue. Animals consume high concentrations of ergot alkaloids in the spring, then suffer from severe heat stress that is exacerbated by hot summer temperatures.

It is now known that ergot alkaloids can be retained in fat tissue. This suggests that fat deposits may serve as a reservoir for toxic alkaloids. Such a reservoir would allow toxins to be released gradually in the months after grazing animals have been removed from infected tall fescue. Retention and slow release of ergot alkaloids from the fat tissue may explain not only why toxicosis symptoms are observed in hot summer months, long after seedheads containing high toxin concentration have been consumed, but also why symptoms such as rough hair coat continue to be observed in feedlots long after cattle are removed from pastures (Figs. 10 and 11). Also, the retention of alkaloids by fat tissues may provide clues to the cause of fat necrosis.

Tall Fescue Toxicosis and Management

Fig. 10. Feedlot performance (lbs per animal) of beef cattle after grazing three types of tall fescue: E+ (infected with toxic endophyte), E- (not infected with an endophyte), and E++ (reinfected with a beneficial endophyte) . Cattle that previously grazed E- and E++ tall fescue entered the feedlot 117 pounds heavier finished 108 pounds heavier than cattle that grazed E+ tall fescue.

Tall Fescue Toxicosis and Management

Fig. 11. Steers in feedlot after they grazed tall fescue with beneficial endophyte (in foreground) or tall fescue with toxic tall fescue (background). (Photo by Susan Duckett.)

An early solution: Endophyte-free tall fescue cultivars.

Fescue toxicosis was partially solved in the 1980s, when it was reported that cattle grazing tall fescue pastures with low endophyte infection rates gained weight more rapidly than cattle grazing highly infected pastures (16). These grazing trials encouraged plant breeders to remove the endophyte from tall fescue (26). The new endophyte-free cultivars produced no symptoms of toxicosis in livestock. When compared to their infected counterparts in side-by-side feeding trials, the new endophyte-free cultivars dramatically increased rate of gain, reproductive performance, and milk production (Table 1). It could be said that the new cultivars rendered tall fescue a nontoxic and highly nutritional cool-season grass.

Table 1. Decline in animal performance among livestock fed either high- (61 to 100%) or low-endophyte (0 to 8%) tall fescue. As a rule of thumb, steer gain decreases 0.10 lb/day for every 10 percent of infected plants in a pasture .

Location of research Change in animal
performance

(relative to control)
Class of
livestock
Forage or
feed type
                                    Average daily gain (lbs)
Alabama -0.84 Steers Hay
Alabama -1.67 Steers Seed
Alabama -0.84 Steers Pasture
Kentucky -0.55 Steers Pasture
Georgia -0.29 Steers Pasture
Alabama -0.77 Steers Pasture
Texas -1.12 Steers Pasture
Arkansas -0.44 Steers Pasture
Mississippi -0.48 Steers Pasture
Missouri -0.90 Steers Pasture
Virginia -0.53 Steers Pasture
Oklahoma -0.51 Steers Pasture
Tennessee -0.42 Steers Pasture
                                    Milk production (lbs/day)
Alabama -11.00 Beef cows Pasture
Kentucky -16.94 Dairy cows Green chop
Missouri -3.96 Beef cows Pasture
                                    Intake (lbs/day)
Alabama -1.98 Steers Hay
Alabama -8.80 Steers Seed
Kentucky -1.98 Steers Seed
North Carolina -1.10 Lambs Hay
Georgia -4.62 Steers Pasture

Plant persistence problems and the importance of an endophyte.

As producers began planting the new endophyte-free cultivars, they began reporting problems with stand loss. These reports were soon followed by scientific studies that revealed problems with drought tolerance. Endophyte-free tall fescue lacks critical physiological functions that allow plants to recover from drought stress; these drought-related functions, still being explored in research laboratories, are operational in endophyte-infected cultivars. In addition to the drought studies, other research reported that in comparison to infected tall fescue, endophyte-free tall fescue was more susceptible to plant pathogens, insects, overgrazing, and mineral deficient soils.

Recently, researchers have suggested that this lack of persistence is caused by several individual factors that work together in a phenomenon called accumulated stress. An example of accumulated stress in endophyte-free tall fescue can be seen from the dual effects of drought and nematodes; as roots are degraded by nematodes, plants fail to take up moisture and suffer from drought stress, a stress that is already occurring because endophyte-free plants lack drought tolerance mechanisms. The compounding effects of nematodes and drought place the entire pasture at maximum risk.

Recent solutions: Tall fescue infected with beneficial endophytes.

Until recently, producers who preferred to use tall fescue faced a dilemma. They could either plant a traditional endophyte-infected cultivar, such as Kentucky 31, which gives excellent plant persistence but poor animal performance, or they could plant an endophyte-free cultivar, which gives poor plant persistence but excellent animal performance. Now producers have a third choice. They can plant tall fescue infected with a so-called beneficial endophyte, sometimes called a novel or introduced endophyte.

Cultivars with beneficial endophytes are developed by first removing the common endophyte and then replacing it with a new endophyte strain (Figs. 12 and 13). These new endophytes are the same fungal species as the common endophyte found in infected tall fescue, yet they produce little or no ergot alkaloids. Since these fungal strains do not produce ergot alkaloids, tall fescue cultivars infected with beneficial endophytes are considered nontoxic. Beneficial endophytes have been inserted to increase plant persistence, attempting to overcome the major disadvantage of endophyte-free cultivars. Some cultivars infected with beneficial endophytes have been tested extensively in grazing trials with various classes of livestock. Lamb ( Fig. 14) and stocker steer gains ( Table 2) were similar to gains seen on endophyte-free tall fescue. In comparison to cultivars infected with the toxic endophyte, cultivars with beneficial endophytes are grazed for more hours per day and are consumed in larger amounts per day. Tall fescue cultivars with beneficial endophytes are also grazed closer to the ground than is toxic tall fescue, indicating higher forage intake rates for the animal and more intense grazing pressure on the plant (Fig. 15).

Tall Fescue Toxicosis and Management

Fig. 12. Process of creating tall fescue cultivars that are endophyte-free or contain a beneficial endophyte.

Tall Fescue Toxicosis and Management

Fig. 13. Insertion of beneficial endophyte into endophyte-free tall fescue. (Photo by Chuck West.)

Tall Fescue Toxicosis and Management

Fig. 14. Daily gain and prolactin production of sheep grazing tall fescue infected with a toxic endophyte (E+), tall fescue not infected with an endophyte (E-), and tall fescue reinfected with a beneficial endophyte (E++)

Tall Fescue Toxicosis and Management

Fig. 15. Grazing pressure on tall fescue with MaxQ, a tall fescue cultivar infected with a beneficial endophyte (left), compared to tall fescue infected with a toxic endophyte (right). (Photo by John Andrae.)

Table 2. Stocker cattle gains on three types of tall fescue pasture: toxic tall fescue, endophyte-free tall fescue, and tall fescue infected with a beneficial endophyte.

Cultivar Location Pasture Endophyte Status
Toxic
endophyte
Endophyte-
free
Beneficial
endophyte
Average Daily Gain (lbs)
ArkPlus Fayetteville, AR 0.90 1.50 1.40
Mt. Vernon, MO 0.55 1.25 1.25
MaxQ Calhoun, GA 1.03 1.84 1.81
Eatonton, GA 1.14 2.24 1.91

Management of Tall Fescue Toxicosis

Armed with these new cultivars and the knowledge of endophyte toxins, producers can develop management strategies to alleviate tall fescue toxicosis. The most logical way to alleviate toxicosis involves alkaloid management. This refers to the adoption of practices that reduce the amount of ergot alkaloids ingested by the animal. Alkaloid management can involve replacement of toxic tall fescue with another forage, or it can involve a series of practices for farms that retain toxic Kentucky 31. The key to alkaloid management is to begin limiting the ingestion of alkaloids in the pasture long before severe symptoms appear in grazing animals

The first step in management: Get an endophyte test.

The first step in proper management is endophyte testing. At present, there are two methods of testing: a microscopic procedure and a chemical procedure. The chemical procedure was developed by Agrinostics, Ltd. Co. (Watkinsville, GA). It is gaining popularity because it is fast, accurate, and costs about the same as the microscopic test. In addition, the chemical method is performed on a special test paper (Fig. 16); this paper can be stored as a permanent record of endophyte infection level.

Tall Fescue Toxicosis and Management

Fig. 16. A chemical procedure uses special paper to show endophyte infection in tall fescue tillers (left) and seed (right). (Photo by Nicholas Hill.

Both the microscopic and chemical tests report presence or absence of endophyte as a percentage of plants in the field. They do not measure concentrations of the toxins in the plant. However, the tests do reflect animal performance, even without measuring toxin concentrations. As a rule, for every 10% plants infected with the toxic endophyte, steer gains can decrease 0.10 lb/day. Endophyte tests can also determine the proportion of infected seed in a seed lot. Sampling methods for seeds and pastures are specific and should be obtained from the laboratory performing the test.

Option I: Replacement of toxic tall fescue.

If the endophyte test reveals that 20 to 35% of the plants are infected, producers should consider eradicating the toxic tall fescue and replanting the pasture with another grass. It should be pointed out that researchers generally consider infection levels of 20 to 35% as moderate, and they consider levels above 50 or 60% as high.

Replacing toxic tall fescue with a nontoxic forage is the best way to ensure the toxic alkaloids are no longer present. It is also the best way to avoid annual input costs and time commitments that are necessary when a toxic cultivar is retained as the pasture.

When toxic tall fescue is eradicated, it is often replaced with a different forage; however, it can be replaced with a tall fescue cultivar that is either endophyte-free or contains a beneficial endophyte. Before replacing toxic tall fescue with a nontoxic cultivar, the following criteria should be considered:

1. Level of toxic endophyte. If endophyte infection level is low, replacing it with a new cultivar is not usually economically feasible.

2. Land ownership. The replacement process may not be economical for short term rental arrangements.

3. Landscape. Replanting into terrain with steep slopes may not be practical.

4. Livestock class. Pastures that support high value horse breeding programs and grass dairies are strong candidates for replacement with nontoxic tall fescue. Beneficial endophytes improve performance in beef stocker and heifer replacement operations as well, but replacement is more critical with higher-performance animals.

5. Grazing management. If the pasture is to be grazed close to the ground, continuously, and with the same low level of management as used for infected varieties, it may be better to keep the old tall fescue. All replacement grasses will require at least some minimal level of grazing management.

6. Seed production. Some new cultivars that contain beneficial endophytes cannot legally be harvested for seed, so additional income from seed production may not be expected.

Tall Fescue Toxicosis and Management

Fig. 17. Major and minor areas of tall fescue use in the U.S.

When toxic tall fescue is replaced with another tall fescue, cultivars with beneficial endophytes are usually the best choice. Endophyte-free cultivars also can be used successfully in environments that experience limited stress from drought, diseases, and insects, such as the northern regions of tall fescue adaptation (Fig. 17). With proper grazing management, endophyte-free cultivars have sometimes persisted for greater than five years in southern regions of the fescue belt. However, these endophyte-free tall fescue pastures were planted on soils with good water availability, were rotationally stocked, and not grazed during summer months.

Reseeding an old tall fescue field.

Replacement of toxic tall fescue with another cool-season grass commonly employs a process called spray-smother-spray. According to this process, the old tall fescue is sprayed with a systemic, non-selective herbicide (such as glyphosate). The field is then quickly no-till drilled into an annual smother crop that is grazed or cut for hay, and then the field is sprayed again prior to planting the new cool-season grass (Fig. 18).

Tall Fescue Toxicosis and Management


Fig. 18. The spray-smother-spray method of replacing toxic tall fescue in a pasture with another cool-season grass.

The reason for such an involved process is that old stands of well-established tall fescue are not easily eradicated. While a single spray coupled with cultivation may kill most of the existing plants, it does not kill them all. Within a year, escape tillers and viable seed from the seed bank can reestablish the toxic field. The smother crop is used to form a shade canopy over the ground; this prevents aggressive reestablishment of the old crop while providing a source of forage until the new crop is ready to plant. After the smother crop is removed, any escape tillers and volunteer seedlings of toxic tall fescue can be killed by the second spray. The new crop can then be no-till drilled into the stubble. If the new crop is a cool-season grass, and if it forms a healthy canopy, the field will not be re-infected unless the stand thins. This is because only seed or residual surviving plants can spread the endophyte.

This spray-smother-spray technique can be employed with spring or fall plantings. With fall plantings, the toxic pasture should be sprayed in the spring and a smother crop such as pearl millet (Pennisetum americanum) or sorghum-sudangrass (Sorghum bicolor) no-till drilled in late spring. Producers should manage the smother crop as they would normally, carefully monitoring nitrate or prussic acid build-up in the annual grasses. After the smother crop is grazed or harvested, the escape tillers and volunteer seedlings of the old fescue and smother crop are sprayed, and the new cultivar is no-till drilled according to the fall planting recommendations for a particular region. If the spray-smother-spray process is used for spring plantings, the smother crop should be a winter annual, such as wheat (Triticum aestivum), rye (Secale cereale), or another cereal crop. Though the spray-smother-spray process can effectively prepare ground for spring planting into an old fescue sod, the spring plantings are not usually advised because of weed pressure and inability to establish an adequate root system before the summer.

Successful establishment of a new cool-season grass can be expedited with other management methods. Clipping seedheads of the old tall fescue before the seed matures and before spraying prevents a build-up of seed in the seed bank that could reinfect the new stand. Use caution when seeding a companion legume with the new stand. Legumes such as red clover (Trifolium pratense) are aggressive and can form a canopy over the newly-seeded replacement grass. Aggressive legumes should not be seeded until the grass is well established. In addition, seeding legumes at the time of establishment limits the use of broadleaf herbicides. Many legumes are easy to interseed into existing tall fescue sods. Legumes with poor seedling vigor, such as birdsfoot trefoil (Lotus corniculatus), could be seeded at time of grass establishment.

Option II: Management of toxic tall fescue. If replanting is not feasible, there is an entire set of management practices that can reduce alkaloid ingestion in a toxic field. These practices include livestock rotation at key times during the year, dilution of tall fescue in the pasture by interseeding legumes and other grasses, feeding of supplements, fertilizing pastures with low rates of nitrogen, ammoniation of toxic tall fescue hay, and controlling seedheads in the field. While these management practices are effective, they represent recurring cost inputs and time commitments. In addition, several of these inputs must be employed collectively before animal performance can match that observed on nontoxic tall fescue pastures (Fig. 19).

Tall Fescue Toxicosis and Management

Fig. 19. Additive effect of management inputs. With enough inputs, gains from animals grazing tall fescue with toxic endophytes (E+) can approach gains from animals consuming pure stands of endophyte-free (E-) tall fescue or re-infected with beneficial endophytes (E++).

Livestock rotation to other pastures.

Livestock should be moved to pastures other than toxic tall fescue in mid-spring and should graze these nontoxic pastures through the summer months. Rotation to summer pastures is among the most effective and important management practices to employ. The movement off of toxic tall fescue in spring greatly reduces alkaloid consumption because alkaloid levels are highest when seedheads are present (Fig. 20). Grazing the livestock on a nontoxic pasture in the summer prevents the severe depression in performance that becomes worse at high temperatures. It also provides a source of forage when tall fescue is semi-dormant. Rotation to summer pastures has been shown to improve steer gains significantly (1) (Fig. 21).

Tall Fescue Toxicosis and Management

Fig. 20. The toxin ergovaline is highly concentrated in the seedheads. Ergovaline was measured in the late spring.

Tall Fescue Toxicosis and Management

Fig. 21. Rotation to a summer forage other than tall fescue can improve animal gains in both toxic and endophyte-free tall fescue.

Grasses and legumes that can alleviate toxicosis by providing summer pasture include both annual and perennial species. Annuals that can alleviate toxicosis include crabgrass (Digitaria spp.), sorghum × sudangrass, pearl millet, and annual lespedeza (Kummerowia spp). Perennials include the native warm-season grasses, alfalfa (Medicago sativa), caucasian bluestem (Bothriochloa caucasia), and bermudagrass (Cynodon dactylon). Some forages, such as switchgrass (Panicum virgatum), caucasian bluestem, and alfalfa, are most productive when managed as independent pastures. Forages such as bermudagrass can be managed as independent summer pastures, but they can also be overseeded with a winter small grain crop, thereby providing excellent winter pasture on the same field.

Annual lespedeza is rarely managed in independent pastures; instead, it is sown into existing toxic tall fescue stands. Because the production curves of tall fescue and annual lespedeza have little overlap, fescue-lespedeza fields can be managed as a double-crop pasture. The tall fescue canopy is typically clipped in late spring. Clipping not only removes toxic seedheads, it also removes the grass canopy, thereby permitting the annual lespedeza component to emerge (Fig. 22). Thus, the sward changes from one virtually pure stand to another and the properly managed fescue-lespedeza field offers the same benefit as rotating livestock across pasture types.

Tall Fescue Toxicosis and Management

Tall Fescue Toxicosis and Management

Tall Fescue Toxicosis and Management

Fig. 22. Tall fescue-annual lespedeza pastures grow and are grazed more like double-crop than true mixtures. In early spring (shown here), pastures are pure tall fescue. In late spring and early summer, hot weather encourages annual lespedeza. By mid-summer, pastures are nearly pure annual lespedeza, which supplies summer pasture. (Photos by Craig Roberts.)

In the southern states of the tall fescue belt, bermudagrass and crabgrass are used as annual lespedeza is used in the northern parts of the fescue belt. Like annual lespedeza, these warm-season grasses provide a source of nontoxic forage production during summer months. Their production patterns also allow them to emerge as double crops within the pasture when the tall fescue canopy is removed.

Producers should also consider feeding nontoxic hay to animals during winter months instead of toxic tall fescue hay.

Dilution with other forages.

Toxic tall fescue pastures can also be diluted by interseeding nontoxic forages. Forages commonly used to dilute infected tall fescue are the perennial legumes, such as red and white clover (Fig. 23). The clovers are easily established into existing sods, compatible with tall fescue, and able to increase animal gains (Fig. 24). Research in several states has shown that addition of clover to infected tall fescue stands can increase steers gains substantially. One report summarized data from five multi-year studies in Georgia (Calhoun), and Tennessee (Greenville, Knoxville, and Grand Junction). Their summary indicated that adding clover to a toxic tall fescue pasture would allow steers to gain an extra 0.15 lbs more per day over the spring and summer grazing period.

Tall Fescue Toxicosis and Management

Fig. 23. Clovers are the most common forages used to dilute toxic tall fescue and are maintained as true mixtures much of the growing season. (Photo by John Andrae.)

Tall Fescue Toxicosis and Management

Fig. 24. Steer gains improve when clover is added to tall fescue with high and low levels of endophyte. These data were compiled from multi-year experiments conducted on four research farms in Tennessee and Georgia

Tall Fescue Toxicosis and Management

Fig. 25. Dilution of toxic tall fescue can be successful with grasses also. This pasture in Missouri is tall fescue mixed with orchardgrass, smooth bromegrass, Kentucky bluegrass, red clover, white clover, and birdsfoot trefoil. The diverse mixture is maintained by management-intensive grazing. (Photo by Craig Roberts.)

 

While dilution of toxic tall fescue with clover is a good practice, it is not as advantageous as replacing toxic tall fescue with nontoxic cultivars. Livestock gain less on toxic tall fescue-clover mixtures than they do on endophyte-free tall fescue, even when endophyte-free pastures contain no clover. And while diluting toxic tall fescue pastures with clover improves steer gains, adding clover to nontoxic tall fescue has the same positive effect. Dilution, therefore, is only a partial remedy, masking the toxic effects from alkaloids present in tall fescue rather than eliminating the toxins.

Toxic tall fescue can also be diluted with grasses (Fig. 25). It is common in the northern states of the tall fescue belt to establish a blend of cool-season grasses that includes tall fescue, orchardgrass (Dactylus glomerata), and smooth bromegrass (Bromus inermis). These cool-season grass blends are less common than tall fescue-clover mixtures, because orchardgrass and bromegrass are not commonly overseeded into existing tall fescue sods. Rather, these blends are planted in new seedings. Also, unless rotational grazing is employed, infected tall fescue becomes the dominant species by crowding out other grasses under continuous grazing.

Dilution is not equally beneficial to all classes of livestock. Pregnant mares are extremely sensitive to alkaloids in tall fescue. The consumption of even small amounts (10% or less) of toxic tall fescue can have detrimental effects on gestation, parturition, and lactation. This sensitivity is so severe that the aforementioned problems are not offset by diluting toxic tall fescue with other forages or with supplements.

Supplemental feeding.

The feeding of supplements has also been proven to alleviate tall fescue toxicosis. Supplemental feeds often decrease forage intake and therefore dilute tall fescue toxins in the diet in the same manner as legumes or nontoxic grasses do in the pasture. The combination of decreased toxin intake and increased dietary protein or energy from supplements can improve animal performance (Fig. 26). Supplements commonly fed to cattle on toxic tall fescue include grains, oil seeds, and grain milling byproducts. Silage and nontoxic hay may also be used as supplemental feeds.

Tall Fescue Toxicosis and Management

Fig. 26. Average daily gain of growing steers (initial body weight 541 lbs) grazing toxic tall fescue improves when the diet is supplemented with corn and corn gluten feeds

Nitrogen fertilization.

If producers are trying to reduce toxin loads in the field, they should not fertilize E+ tall fescue pastures with high rates of nitrogen fertilizer. Alkaloids contain nitrogen, and ergot alkaloid concentrations are rapidly increased following N fertilizer application (Fig. 27). Severity of both fat necrosis and fescue foot appears to be positively related to high application rates of either nitrogen or poultry litter.

Tall Fescue Toxicosis and Management

Fig. 27. Nitrogen fertilizer increases ergovaline concentration

Hay ammoniation.

The process of treating low quality hay with anhydrous ammonia is called ammoniation. When low quality grass hay is treated, the ammonia breaks down cell wall linkages to render the forage more digestible. The process involves covering sun-cured hay bales with a plastic tarp, adding anhydrous ammonia at a rate of 3% of the weight of the hay, and then allowing the reaction to work over a 3- to 6-week period (Figs. 28 and 29).

Tall Fescue Toxicosis and Management

Fig. 28. Ammoniation: the process of adding anhydrous ammonia to low-quality grass hay.

Tall Fescue Toxicosis and Management

Tall Fescue Toxicosis and Management

Fig. 29B. Before hay is ammoniated, bales (round or square) are stacked and covered with plastic. (Photo by Craig Roberts.)

When applied to toxic tall fescue hay, ammonia also appears to detoxify the hay to some extent. In one study, lambs consuming ammoniated toxic tall fescue hay had higher rates of gain (Fig. 30) and increased concentrations of the hormone prolactin (Fig. 31) compared to lambs fed untreated toxic tall fescue hay. The improved lamb performance was probably due to lower toxicosis rather than increased digestibility; lamb performance did not increase when endophyte-free hay was ammoniated.

Tall Fescue Toxicosis and Management

Fig. 30. Ammoniation of toxic tall fescue hay can improve lamb gains

Tall Fescue Toxicosis and Management

Fig. 31. Ammoniation of toxic tall fescue hay can increase levels of the hormone prolactin.

Recent work reported that ammoniated tall fescue hay had lower ergot alkaloid concentration than tall fescue pasture or silage (Fig. 32). Additional work has shown that ammoniating tall fescue seed aftermath (hay comprised of stems from harvested seed fields) can improve steer performance over the winter.

Tall Fescue Toxicosis and Management

Fig. 32. Ammoniated tall fescue hay has low concentrations of toxic alkaloids

Winter grazing management.

Research in the 1990s reported that ergovaline concentrations were high in fall-grown tall fescue, though no seedheads were present. Recent research has confirmed this and has reported that ergovaline concentration decreases in tall fescue stockpiled in Missouri over the winter (Fig. 33).

Tall Fescue Toxicosis and Management

Fig. 33. Ergovaline concentration decreases over the winter in stockpiled tall fescue grown in northern regions of the tall fescue belt.

This fluctuation of ergovaline over the winter could affect feeding strategy. Normally, stockpiled pasture is grazed early in the winter; hay is fed only when the stockpile has been depleted by grazing livestock. The normal strategy forces cattle to graze the stockpile when it contains the highest concentration of ergot alkaloids and then provides cattle with hay when the pasture is least toxic. Feeding hay early in the winter and grazing stockpile later could reduce the amount of ergovaline ingested over the winter feeding season.

Seedhead control.

Seedheads contain 5 times more ergovaline than leaves or stems. Therefore, ingesting seedheads causes severe cases of tall fescue toxicosis. Seedheads can be controlled effectively by clipping. Clipping seedheads in cool-season pastures is a routine practice in New Zealand grass dairies and it is justified solely to maintain a high forage quality. Clipping seedheads should be considered effective in tall fescue pastures as well. Clipping not only maintains forage quality, it also reduces alkaloid concentration in the pasture.

Seedheads may be controlled in the future by application of plant growth regulators to pastures. Ongoing research has reported that certain herbicides can do this also. When some herbicides are applied at low rates, they nearly eliminate seedheads and reduce ergot alkaloid concentration five-fold. There are potential problems associated with this practice, however. When applied at the incorrect rate or at the wrong time, these same herbicides can kill 90% of the pasture. It will be several years before chemical treatment of pastures becomes a feasible option for reducing ergot alkaloid concentration in the field.

Domperidone.

A unique management option for horses involves administration of domperidone, commercially marketed as Equi-Tox. The alkaloids present in toxic tall fescue mimic the neurotransmitter dopamine. This mimicking action overwhelms receptors for dopamine and reduces blood prolactin. This ultimately results in the negative reproductive effects of tall fescue toxicosis. However, ingestion of domperidone blocks receptors of dopamine and increases blood prolactin and progesterone of mares grazing tall fescue . Domperidone-treated mares grazing tall fescue pastures have shorter gestation lengths, live foals are born closer to their expected delivery dates, mares have higher prolactin and progesterone levels, and mares have better mammary development. In addition, treated mares are not agalactic.

Oral dosing of domperidone paste should be started 20 days prior to the expected foaling date if mares remain on toxic fescue up to parturition. If mares are removed from tall fescue prior to parturition, it is recommended that domperidone treatment be started 10 to 14 days prior to the expected foaling date depending on the condition of the mare’s udder. If udder development is normal, mares will probably not require treatment. Domperidone must be obtained from a licensed veterinarian.

Other management practices.

There are other practices that may reduce symptoms of toxicosis, mainly by reducing heat stress of the grazing animal. Data supporting these practices are limited and inconsistent; as such, these practices are considered marginally effective. They are mentioned in this guide because producers often ask about them.

One practice that may reduce heat stress is treatment with ivermectin. Ivermectin is a dewormer commercially marketed as Ivomec. Beef steers grazing toxic endophyte-infected tall fescue have shown greater performance response to ivermectin than similarly treated steers which grazed endophyte-free tall fescue. Dewormed animals also appeared to show fewer clinical symptoms of tall fescue toxicosis than untreated animals. Ivermectin has also been shown to reduce high core body temperature when administered to rats.

Another practice is the feeding of a seaweed-based feed supplement sold under the trade name of Tasco. Tasco has been shown to produce a short-lived reduction of rectal temperatures in beef cattle grazing toxic tall fescue. However, the effect of Tasco on heat stress was typically short-lived and was inconsistent across trial locations. In addition, Tasco has not improved animal gain.

A third practice, popularized in research updates but not yet available to the public, involves treating animals with nitric oxide. Nitric oxide is a vasodilator. Patches containing nitrous oxide have been applied to beef cows to offset vasoconstriction, thereby permitting increased blood flow to extremities and the dissipation of heat. Whether or not this treatment is proven effective and becomes available to the public depends on progress in research and commercialization.

There are other practices that are proposed to alleviate tall fescue toxicosis, although there is little data to support them. Many mineral mixes are sold as cures for fescue toxicosis. The mineral mixes seem to help those animals suffering from mineral deficiencies; however, they have no proven effect on alleviating tall fescue toxicosis. In addition to mineral supplements, there are vaccines against specific fescue toxins that are currently being tested. To date, no vaccines have prevented long-term symptoms of tall fescue toxicosis.

Summary

Tall fescue toxicosis is a serious problem for all classes of domestic livestock but producers can manage it. They should first test their fields to determine endophyte levels and then develop the best management strategies for their farms. Producers can eliminate ergot alkaloid problems by converting the old tall fescue pastures to new cultivars that are endophyte-free or infected with beneficial endophytes. Alternatively, they can employ both new and old management practices that limit the ingestion of toxic alkaloids and improve the health of their livestock and the profitability of their operations.

Source: Craig Roberts, Department of Agronomy, University of Missouri,  John Andrae, Department of Crop and Soil Sciences, University of Georgia