Fescue Foot, Ryegrass Staggers, and Fescue Toxicosis
When Neotyphodium endophytic fungi result in the production of high enough concentrations of toxins in either tall fescue or ryegrass straws, cattle consuming straw from these plants may suffer from serious, sometimes fatal, diseases. Both of these grass-fungus associations (see Chapter 14) produce various alkaloids (see Chapter 13) that have been identified as causal agents of the diseases (see Chapter 1).
In the case of tall fescue, consumption of grass containing ergovaline and related ergot alkaloids, especially in hot weather, can result in fescue toxicosis. If high rates of N fertilizer have been used, regardless of the season, fat necrosis may develop (see Chapter 16). The most serious disorder resulting from the ingestion of endophyte infested straw is fescue foot, a broad term covering symptoms of gangrene and necrosis of body extremities. Ergot alkaloids cause constriction of blood vessels, a condition aggravated by cold weather, which is the time when such straw is fed most often. Signs of fescue foot may appear 2 to 3 wk after ingestion of infested straw or seed screenings. Not all animals are equally susceptible. Persistent cases lead to severe reduction of blood supply to the feet, ears, and tails, with resultant dry gangrene and possible loss of those body parts (Aldrich-Markham et al., 2003; Tor-Agbidye et al., 2001).
At least two major outbreaks of fescue foot occurred in Oregon in 2005. In eastern Oregon, a beef cow-calf operation with more than 1800 animals fed tall fescue straw purchased from the Willamette Valley beginning in late November. By 25 December, when temperatures had ranged from -17 to -1°C, signs of lameness and swollen feet were noted, progressing to dry gangrene of the feet, often with subsequent fracture of the necrotic toes or lower limbs. Three weeks later, the feeding of straw was stopped. By early March, two-thirds of the bulls and almost one-third of the cow herd had died or had to be euthanized. All surviving animals in the herd were under stress and in discomfort. Subsequently, straw samples were found to contain extremely high concentrations of ergot alkaloids. Prior testing would have identified this feed as very high risk and therefore could have prevented this catastrophe.
The other outbreak, in the lower Willamette Valley, affected 330 cows and 10 Angus bulls that had been fed pelleted tall fescue with seed screenings, starting in mid December. By February, when there had been periods with temperatures below -7°C, about 10% of the herd suffered severely from fescue toxicosis, and many had to be euthanized. Samples of pellets taken in January from the bins used for storing the feed showed that the concentrations of ergovaline and ergotamine were at dangerously elevated levels.
Perennial ryegrass contains a somewhat different profile of alkaloids from tall fescue when infected with its endophyte, N. lolii. Infected perennial ryegrass contains lolitrems, peramine, and paxilline in addition to ergovaline (Hovermale and Craig, 2001; Rowan, 1993). The primary disorder associated with N. lolii is ryegrass staggers (Fletcher and Harvey, 1981), of which the causal alkaloid is lolitrem B (Blythe et al., 1993; Fisher et al., 2004; Galey et al., 1991; Gallagher et al., 1984; Hunt et al., 1983). Early-stage ryegrass staggers is characterized by a stiff limb gait and disorientation in affected animals. The disorder progresses to ataxia (involuntary body movements), muscle tremors, and reluctance or inability to rise. Excitement worsens these signs. Animals not withdrawn from feed containing high levels of lolitrem B can exhibit a down convulsive state, but seldom die. Withdrawing the animal from such feed usually results in a return to normal status in several days, although in some cases it may take as long as a few weeks, depending on the severity of the signs.
A practical management procedure to avoid these diseases is to dilute toxic feed with nontoxic feeds to decrease the concentration and thus intake of toxic alkaloids. This management tool currently is in use to decrease toxicosis cases in Japan and the United States.
There have been several reports of fescue toxicosis in Japan with tall fescue straw exports from Oregon. Some beef cattle receiving straw mixed with various other feeds developed anorexia and lameness and had to be euthanized. The Japanese Ministry of Agriculture (MAFF) reported high ergovaline levels in the straw (Saiga, 1998). Perennial ryegrass also is exported to the Pacific Rim countries; it is used primarily as forage for Japanese Black Cattle because it imparts white marbling in Kobe beef. Several instances of perennial ryegrass staggers have been reported as a result of high lolitrem B levels in the perennial ryegrass (Saiga and Maejima, 1998; Miyazaki et al., 2004). Such situations, if repeated, could severely diminish the exports of straw from the Pacific Northwest.
Endophyte toxins from tall fescue also are suspected to afflict New World camelids such as llamas, although the number of animals involved is small (Oregon State University Veterinary Hospital, personal communication, 2007). Typical signs observed in some animals include poor milk production (Brendemuehl, 2002) and sloughing of distal extremities (Davis, 2002). In addition, ingestion of high levels of lolitrem B from perennial ryegrass has been associated with tremors in camelids (Smith, 2002).
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