Perennial Ryegrass Staggers
Also known as
Ryegrass staggers and migram
Perennial ryegrass can cause problems for livestock and may cause two very different conditions. One is liver damage with resulting photosensitization (caused by a fungus called Pithomyces chartarum growing on the ryegrass) and the other is incoordination, caused by mycotoxins produces by the endophytic fungus originally called Acrimonium lolii and now called neotyphodium lolii.
This tiny fungus lives in the plant between cells, particularly in the leaf sheath and seed heads. The fungus is not harmful to the plant, and benefits it in a symbiotic relationship by enhancing seedling vigor, tillering, seed production, resistance to drought and some insects.
However, the fungus produces alkaloids which can produce toxic effects in livestock grazing infected pastures, particularly between late spring and early winter.
Different cultivars of perennial ryegrass vary in their degree of contamination with this fungus; some are only about 30% infected and others are 100% infected.
About 90% of established perennial ryegrass plants are infected with the endophyte fungus. Commercially bred varieties of perennial ryegrass have their seed inoculated with this endophyte fungus to make it hardier (similar to the effect of another endophyte fungus on certain fescue grasses).
The fungus produces alkaloids that are harmful to insects, ensuring better pasture persistence, but can have toxic effects in livestock when eaten in sufficient quantity. Ryegrass breeders continually search for ryegrass variety/endophyte combinations which balance palatability, persistence/hardiness, and livestock safety.
The staggers occur most commonly in the fall if weather is dry—when the grass is dry and short and only making a small amount of growth (with toxins more concentrated in the tissues and seed-heads). If it rains and the grass starts growing rapidly, there is usually no more incidence of the disease.
The incidence of staggers may be variable in a group of animals but only rarely causes death. It may cause bulls to have lower levels of testosterone. Toxins from the fungus also affect blood supply to the skin, causing animals to overheat readily, with inability to handle hot weather.
They may walk into streams or ponds in an effort to cool off.
Reduced blood flow to the skin and extremities hinders the ability to regulate body temperature, leading to heat stress. Sheep and cattle may seek shade, reducing grazing time, and may crowd into dams, troughs and streams, sometimes resulting in mass drownings.
Reduced blood flow to the extremities may also create foot problems. Toxins may disrupt digestion, leading to scouring.
The neurotoxic condition can occur in livestock of all ages occurs in late spring, summer, and fall--only in pastures in which perennial ryegrass (Lolium perenne) or hybrid ryegrass are the major components. Sheep, cattle, horses, farmed deer, and llamas are susceptible.
In New Zealand, a high incidence most years causes considerable loss and seriously disrupts management procedures and stock movement. Perennial ryegrass staggers occurs sporadically in parts of North and South America, Europe, and Australia.
Signs develop gradually over a few days. Slight head tremors and nodding movements are the first signs noted in animals that are approached quietly and watched carefully. Noise, sudden exercise, or fright elicits more exaggerated signs of head nodding with jerky movements and incoordination when the animals try to move.
If they try to run, leg movements are stiff and bounding with extreme incoordination—which often results in collapse. After the animal falls down it usually lies flat with backward arching of the head and neck, rapid involuntary movement of the eyes, and flailing of stiffly extended limbs.
In less severe cases, the attack soon subsides, and the animal regains its feet within a few minutes. If the animal again tries to run, however, the episode is repeated. Signs are most severe when the animal is heat stressed.
If the animal is unable to rise, it becomes susceptible to dehydration, starvation and attack by predators. Deaths also result from mishaps due to lack of coordination, such as drowning in creeks and ponds.
Less obvious signs may include doing poorly (especially in young stock), heat stress, scouring, reduced fertility and lowered milk production, which all contribute to production losses and animal welfare concerns even when staggers are not seen.
- Head tremors and nodding,
- Jerky movements
- Stiff gait
- Arched back,
- Falling down
- Flailing legs
There are several neurotoxins responsible for these signs, due to the alkaloids produced in perennial and hybrid ryegrasses infected with the endophytic fungus Neotyphodium lolii.
The amounts of fungal growth and toxins in infected plants increase to high levels as the temperature rises in late spring. They decrease to safe levels in the cooler seasons.
The branching, threadlike growing portions of the fungus are present in all above-ground parts of infected plants but especially concentrated in leaf sheaths, flower stalks, and the seeds.
Viability of the fungus gradually declines when infected seed is stored at average temperatures and moderate to high humidity, so that few seeds contain viable endophyte after 2 years of storage.
It is thought that the incoordination observed when animals are exposed to the toxin is caused by interference with neuron transmissions in the cerebellum; no specific lesions are seen at necropsy. N. lolii also produces the alkaloid ergovaline, which is responsible for fescue toxicosis.
Ergovaline raises the temperature of animals in warmer months of the year, inducing heat stress. It also depresses prolactin levels; reduced milk yield in cows has been recorded in affected cattle in New Zealand and Australia.
Within various herds, individual susceptibility varies greatly, and this trait is heritable. In outbreaks, morbidity (number of animals affected in the group) may reach 80%–90%, but mortality (number that die) is low (0–5%). Deaths are usually accidental, by drowning when drinking from ponds or streams, or due to inability to forage for food and water.
The strict seasonal occurrence of characteristic tremors, incoordination, and collapse in several or many animals grazing perennial ryegrass pastures strongly implicates this disease. Annual ryegrass staggers and paspalum staggers have similar clinical signs and seasonality, but microscopic examination of the leaf sheaths of the ryegrass sward will reveal the extent of endophyte infection.
Because the endophyte and the lolitrems and ergovaline are not uniformly distributed within ryegrass plants, control by grazing management can help reduce or prevent the disease. Lolitrems and ergovaline are concentrated in the leaf sheath.
If pastures are not overgrazed down into the leaf sheath zone or grazed when the plants are flowering, the animals should be relatively safe even when a high proportion of the ryegrass plants are infected with endophytes.
Encouragement of growth of other grass species and legumes in established pastures also reduces the intake of toxic grass.
Safe new pastures can be established using ryegrass seed with little or no endophyte infection. Existing pastures can be over-seeded with legumes and/or non-toxic grass species to dilute the toxin. The best solution may be to renovate pastures after first eliminating old perennial ryegrass plants and seeds that contain the endophyte fungus.
Alternatively, seed that has been stored at ambient temperatures for 2 years probably contains few viable endophytes and would produce nontoxic pastures. Cultivars of ryegrass artificially infected with a strain of endophyte that does not produce lolitrem B or ergovaline are available in New Zealand.
Signs of ryegrass staggers have not been seen in animals grazing these grasses. A strain of Neotyphodium that produces different compounds has been developed, and offers insect resistance with the trade-off of sporadic occurrence of low-level staggers.
There is no specific treatment. If the cattle can be removed from the pasture, no treatment is required, since recovery is rapid after they are no longer grazing the endophyte-infected grasses. Recovery occurs within 1 to 4 weeks.
In mild cases of staggers, the animals should be left undisturbed or quietly moved to a safer pasture with a water trough, rather than open water, to avoid the risk of drowning. In more severe cases removal from toxic pasture is vital, but may take several days, to reduce the number of animals that collapse and require intensive nursing or destruction.
If removal from toxic pasture is not an option, stock can be confined in temporary containment areas with a safe water supply, shade and supplementary feed. Feeding hay or concentrates on toxic pasture is often unsuccessful, as the mere act of driving a vehicle to the animals may cause them to run, stagger and collapse.
Collapsed animals should be moved to sheltered yards or sheds if possible and provided with shade, food and water. Animals should be positioned upright, rather than on their sides, to avoid regurgitation of stomach contents and aspiration into the lungs. Some producers have successfully used fence panels and to position affected stock.
Most will improve within a day or two and can then be moved to yards or sheds for less intensive nursing.
A variety of drugs, vitamins and minerals have been tried, in efforts to alleviate toxicosis, but there is little scientific evidence to support their use. Consult your veterinarian regarding appropriate treatment. If animals are collapsed and you are unable to provide sufficient feed, water and shelter, they should be humanely destroyed.