Perennial Ryegrass Staggers
Dr Colin J Scrivener BVSc.
Senior consultant, Mackinnon Project
University of Melbourne
250 Princes Hwy, Werribee Vic 3030
In: Plant toxins and their effects on animal welfare. Paper presented at the Animal Welfare Centre Scientists' Meeting, 17th May 2002, Victorian Institute of Animal Science, Mickleham Road Attwood, Victoria.
Ryegrass staggers has effected very large numbers of sheep throughout Victoria during the autumn. The stagger syndrome is caused by tremorgenic mycotoxins produced by the endophyte fungus Neotyphodium (Acremonium ) lolii that infects the early growth and germinal parts of perennial ryegrass, Lolium perenne.
There have been many reports of unusually large numbers of deaths among sheep. In one case 1200 sheep are reported to have died. In cases reported to the Mackinnon Project, sheep deaths have exceed 10%-15% in some flocks with up to 50% of mobs exhibiting some degree of staggers. Staggers and deaths are occurring in all classes of sheep and with sheep ranging from condition score CS2 - CS4.
Deaths have occurred where sheep have gone down, in all areas of the paddock, and have not been limited to 'the result of misadventure' or as 'usually accidental'. Significant numbers of deaths have occurred as sheep have gone into water courses/dams and are often found stuck in water troughs and this has possibly lead to the belief in death by misadventure.
Dead sheep are found where they have gone down, sometimes in sternal recumbency but usually in lateral recumbency. Death at this stage may be related to the total and ratios of toxins, especially lolitremB and ergovaline, but may be indirectly caused by starvation, reduction of rumen function, lack of water intake , toxin induced dehydration and possibly due to hyperthermia. The relationship to death rate related to changes in ambient temperature and sunlight has not been reported. Unless management takes a role, most deaths are lingering and can involve flystrike and predator attack. On one property foxes have been responsible for the final death of over 60 sheep that had gone down.
Outbreaks of staggers in cattle have not been reported to the Mackinnon Project but we have seen a number of incidences where cows have been more irritable in yards. Cows have shown signs such as excessive walking in the yards, increased kicking out and are more jumpy while being rectalled for pregnancy testing.
Sheep, cattle and other livestock can be effected. A plant fungus in the germinal or early growth of the plant produces toxic alkaloids. The main ones are lolitremB, ergovaline and peramine. The level of each toxin supposedly increases with moisture stress and high temperatures, high humidity and with increased fertiliser. However the proportion of each toxin can vary under, unspecified, conditions. Hay aftermath may be particularly toxic and regrowth protected under an overgrown canopy may be high in toxin. The use of Roundup(TM) to 'freeze' pasture may reduce or dilute the level of toxin ingested in the grazed pasture, but has no direct effect on increasing the toxicity of the plant material.
The clinical signs of perennial ryegrass staggers include:
The total toxin load and probably differences in the ratio of the various toxins produced by the Neotyphodium produce variations in the combination of signs and sequelae to perennial ryegrass poisoning.
The obvious signs of staggering are attributed to the lolitremB:
- Head shaking, nystagmus (eye flicking)
- Gait changes; stiffness, variable degrees of stagger often with the animal on their knees increasing to complete loss of control in the ability to walk in a given direction
- Recumbency; going down, usually ending on its side in a tetanic spasm
- Dags and increased flystrike and reduced growth rates ie "weaner ill-thrift"
- Reduced lamb survival
- Long term effects on maiden ewes of decreased lactation at subsequent lambings
In most outbreaks, deaths are reportedly due to inadvertent accidents such as falling in dams or getting caught in fences. However, in severe outbreaks such as experienced this year (2002) and during 1993, large numbers of sheep have died in the paddock. Sheep are found in sternal or lateral recumbency, will stagger severely and generally fall over again when stood up: then they die there.
Dehydration, hyperthermia, absolute starvation, hypoglycaemia ("pregnancy toxaemia") and predator attack may contribute to the subsequent death of the animal.
Ergovaline is the second toxin produced by the fungus. It causes an increase in body temperature with an increase in respiration rate, a decrease in prolactin hormone levels (and less milk production) and decreased rumenoreticular and gut activity with less water retention. These changes on top of the staggers caused by the lolitremB could well be sufficient to cause the direct death of the animal: at this stage we don't know the full causation effects.
Clinically we have found increased body temperature, >41°C, variable scouring, increased respiratory rate and severe muscle twitching over the trunk and legs as well as head tremour and nystagmus. Blood parameter changes have been variable and have been compounded with flystrike etc. Calcium levels have been within the normal range, sodium is slightly elevated and magnesium has been slightly reduced.
Several treatments are being trialed, however at this time there are no reliable treatments to reverse the clinical condition. We have tried sedatives such as Promazine, relaxantants such as Diazepam, metoclopramide (Maxolon(TM)) a dopamine antagonist and domperidone (Motilium(TM)) another dopamine antagonist. All treatments were either 1 or 2 day treatments and we have had no reports back of substantial improvement. One treatment with metoclopramide did appear to improve the condition and one sheep treated with domperidone did appear to improve the sheep. At the time of writing, we are still awaiting reports from sites where treatments have been carried out. We have not attempted treatments over longer periods though the slow response when sheep are removed from the source of toxin suggests that longer term treatment may be more beneficial.
Treatment with Calcium-borogluconate, alone or in combination with glucose, magnesium and phosphorus or with magnesium sulphate solution gave no beneficial response other than an initial stimulus to sheep that had just gone down.
Control of PRS
Control of the condition, and its effects, depends upon management changes.
- Move the sheep to ryegrass free pastures
- In mild outbreaks, avoid mustering and droving - don't use dogs. If necessary to change paddocks, open the gates and let sheep drift through. If necessary to move sheep do it slowly and transport any sheep that go down
- Feeding hay and grain may increase feed 'substitution' and dilute toxin intake
- Pick up and support sheep (tie to the fence) any sheep that have gone down. Anecdotal evidence says sheep will respond better the faster they are picked up
- Calcium borogluconate or 3-in-1 will initially help the sheep to get up
- Gluing a patch over one eye has been reported to improve their balance
The question is how to predict when a mild outbreak will become a severe outbreak such as we are experiencing at present.
Expensive stock such as rams should be moved to ryegrass free areas - the front lawn - or hand fed in a small pen. Stomach tubing electrolytes to rehydrate them could be required and giving an energy supplement such as Vytrate(TM) could be beneficial.
Flock sheep will be difficult to treat but at their present value a complete feedlot situation could be the best economic solution.
Original article written 17th April 2002.
Adult wethers can be maintained in a feedlot on oats at 2.7 - 3 kg/hd/week.
Autumn lambing ewes would need to have significantly more feed than this, say 5 - 6 kg/hd/week. There may be problems in moving staggering sheep into the feedlot.
Some areas have received sufficient rain for pastures to commence growing which will decrease the amount of toxin eaten by each animal leaf and companion plants start to grow.
In those areas where rain has not been sufficient to cause the autumn break there is a 50% probability of sufficient rain by ANZAC Day and sufficient feed available by mid-May. In dry areas if a break occurs by the end of April the likelihood of having to feed ranges from 2 to 6 weeks. This will require 6 -15 kg/hd for wethers and 12 to 30 kg/hd for ewes.
At current prices for oats ($170 + freight) and lupins ($325 + freight) this should cost between $1.20 - $3 for wethers and $2-40 - $6 for ewes. With a 10% expected death rate this is the equivalent to a cost of $24 to $60 per ewe saved; at a 20% death rate it is the equivalent of $12 to $30 per ewe saved.
A series of Agriculture Notes are available from the Department of Natural Resources and Environment web site: http://www.nre.vic.gov.au/notes/
AG0700, Perennial ryegrass staggers / ill thrift;
AG0713, Perennial ryegrass;
AG0863, Toxins in endophyte infected perennial grasses;
AG0202, Endophyte in perennial grasses- effect on host plants and livestock;
AG0129, Annual ryegrass toxicity;
AG0482, Pasture grasses approved for Victoria, 1997
A summary on Perennial Ryegrass staggers is also available from the Grassland Society of Victoria inc. Newsletter; January 2002. (author: Kevin Reed).
The Animal Welfare Science Centre was established by the University of Melbourne, Monash University and the Department of Primary Industries, Victoria. The Centre focuses and coordinates the research and academic resources of the three collaborating organisations, providing the animal industries, animal users, the farming community, Government, the general community and the academic community with an internationally competitive research, teaching and training resource in animal welfare.