Ryegrass staggers can be a serious problem in livestock grazing perennial ryegrass pasture during the summer and autumn months. It is most commonly seen in sheep and cattle, but horses, deer and alpaca are also susceptible. While ryegrass staggers has not been recorded in goats, they may also be susceptible but may not develop symptoms due to their different grazing/browsing habits.
Affected animals develop muscle tremours and incoordination which worsens with stress and external stimuli. They may have a stiff gait, which can progress eventually to paralysis. This is not the same disease as grass tetany (which is sometimes referred to as grass staggers). Ryegrass staggers is caused by a group of toxins that accumulates in the leaf sheaths of perennial ryegrass, whereas grass tetany is caused by low blood magnesium.
What Causes Ryegrass Staggers?
Perennial ryegrass (Lolium perenne) is one of the most commonly sown pasture grasses in Australia. Most established perennial ryegrass plants are infected with a native endophyte fungus known as Neotyphodium lolii. This fungus grows within the leaves, stems and seeds of perennial ryegrass and produces alkaloids which can have toxic effects on grazing livestock. These toxins accumulate in the plant - peaking in summer/autumn and may remain high in the pasture for five to six months. Silage made during this time may also retain similar concentrations of toxin as the source grass for more than 200 days. In hay the toxins appear to decline significantly over a similar period.
Neither the fungus nor the toxins adversely affect the plant. In fact, the presence of the fungus increases seedling vigour and the productivity of mature plants. Also, the toxins deter a wide range of insect pests from attacking infected plants and interfere with the lifecycle of the ryegrass stem weevil.
The fungus can only spread to ryegrass plants from infected seeds as it lives entirely within the plant and does not produce spores. It cannot spread from plant to plant in the field. The fungus has only a short life (18-24 months) in the seed under normal grain storage conditions.
Seed with a high fungus content that is sown in the first autumn after harvest (ie infected seed that is approximately three months old), will produce pastures with a high proportion of infected plants. The same seed sown one year later will give a lower and more variable level of infection, while two-year-old seed will produce pasture that is virtually free of fungus.
How are Stock Affected?
The symptoms of ryegrass staggers usually develop 7-14 days after stock start grazing the toxic parts of the plant. As the fungus and the toxin occur mainly in the leaf sheaths very close to the ground, hard grazing of infected pasture is likely to induce ryegrass staggers. Younger animals tend to be worst affected.
Mildly affected animals develop tremours but these symptoms become more severe when they are exposed to physical stress such as mustering and external stimuli such as humans, dogs, vehicles and noise. So the acute problems created by this disease often occur when trying to move affected animals. They lose coordination and develop a stiff gait or may be unable to walk. As the condition worsens animals may collapse, have convulsions and be unable to rise, leaving them susceptible to predation, dehydration and starvation. The toxins can induce high body temperatures so animals will try to cool themselves in mud wallows, dams and troughs, sometimes drowning or otherwise injuring themselves in the process. Even when toxin concentrations are too low to cause staggering, there is growing evidence that the toxins may cause chronic production losses including ill-thrift and reduced liveweight gains in young stock, lowered fertility and reduced milk yields. Prolonged exposure to toxic pasture can lead to permanent neurological damage.
The typical symptoms of ryegrass staggers are listed below:
- Behavioural changes - more flighty
- Slight tremor of the head and twitching of muscles in the neck, shoulder and flank.
- Nodding of head and jerky limb movements.
- Swaying and staggering.
- Stiff stilted gait, short prancing steps to stiff legged bounding gait.
- Collapse, extension of head, arching of back, rigid tetanic extension of legs.
- Behavioural change - more flighty
- Leg and trunk stiffness causing hesitancy in movement.
- Tendency to fall, stand with legs splayed out.
- May kneel on forelegs or 'dogsit' on hind legs.
- Collapse, flexion rather than extension of legs.
- Turn with difficulty, stand with legs splayed out, tendency to fall.
- Reeling drunken gait, move slowly.
- Paralysis of hind quarters.
- Trembling, muscle spasms, hypersensitivity to sudden stimuli.
There is no specific therapy for perennial ryegrass staggers. In mild cases, stock should be very quietly moved, without a dog, to a safer paddock with a water trough rather than open water to reduce the risk of drowning. Excitement during this time must be minimised to reduce the number of animals that collapse and then require intensive nursing or euthanasia. Collapsed animals should be moved to sheltered yards or sheds and provided with shade, food, water and nursing care. It is of utmost importance that affected animals are managed appropriately - those that can no longer fend for themselves must be nursed or humanely destroyed. Animals that are not severely affected recover two to three days (sometimes up to 14 days) after they are transferred to 'non-toxic' pasture. The rate of recovery will, amongst other things, depend on how free of toxin is the 'non-toxic' pasture.
Preventative measures include the fencing of dams and waterways and ensuring an alternative feed supply is available. Monitoring the animals is vital so that the early signs of staggers can be detected and the animals moved to safe pastures.
Controlling the Disease
Avoid stock management practices that encourage animals to graze close to the ground. Maintain a close watch on stock whenever feed is in short supply because most problems occur at these times. Consider feedlotting weaners during the peak toxin period.
If feed regularly becomes very short throughout a property, sow pastures of other species (eg. cocksfoot, phalaris) or forage crops for grazing in the summer-autumn period. Perennial ryegrass with low endophyte or non-toxic endophyte is becoming increasingly available.
Set-stocking often leads to uneven grazing, with small areas of the pastures grazed closely and the rest untouched. However, a rotational grazing system that leaves very short stubbles (such as block grazing with a two to three day grazing period) may also lead to staggers. Moving stock daily, so that longer stubble remains, can avoid this problem.
The choice of pastures and their management can also reduce the incidence of staggers. Appropriate practices include:
- Block grazing and balanced fertiliser use, to promote pastures with a high clover content.
- Using mixed pasture swards containing cocksfoot, tall fescue, prairie grass and phalaris, to reduce the ryegrass content of the pasture.
- Sowing pasture with perennial ryegrass seed that is at least 15 months (and preferably two years), old, as the fungus dies in the seed under normal storage conditions. However, these pastures may be less productive and persistent than those with a high level of fungus infection.
There is no evidence to support claims that the use of different fertiliser regimes, or the application of salt or other additives to the sward or drinking water, will prevent or cure staggers while stock continue to graze infected pastures.
Annual Ryegrass Toxicity
This is a distinctly different disease to perennial ryegrass staggers although the similarity of the names often causes confusion.
Annual ryegrass staggers occurs when stock graze Wimmera ryegrass Lolium rigidum at or after heading and the seed heads are infected with a particular type of nematode and species of bacterium. The bacteria produce a toxin that is fatal to stock.
The disease is confined to areas of Western Australia, South Australia and Victoria. It has not been detected in Tasmania to date, neither have pastures or grass seed infected with the nematode and bacteria.
The Seeds Regulation prohibits seed containing the nematode from being imported to, or sold in, Tasmania.
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