Phalaris toxicity can cause both a sudden death syndrome and a staggers syndrome. 'Phalaris staggers' is an in- coordination syndrome that is associated with the ingestion of some varieties of phalaris (Phalaris aquatica) at a time when it contains toxic alkaloids. The staggers syndrome can also cause death in severely affected animals through heart failure. Sheep of all ages are affected and cattle may also be affected. Cattle are less susceptible than sheep but it affects the nerves that control the tongue and swallowing, so affected cattle are unable to eat normally and can suffer a high degree of weight loss.
'Phalaris sudden death' is thought to be a completely separate syndrome to 'Phalaris staggers'. The sudden death syndrome also occurs in autumn to early winter, but occurs within 36 hours of introducing stock onto phalaris pastures. The sudden death syndrome is proposed to occur as a result of ingesting a compound in phalaris that decreases nitrogen metabolism, resulting in peracute ammonia poisoning. It takes sheep 24 hours to develop effective nitrogen metabolism on phalaris.
Provision of oral cobalt protects against phalaris staggers. It appears to stimulate the proliferation in the rumen of microorganisms which are capable of destroying the causative agent/toxic alkaloid that causes the staggers syndrome. Cobalt has no preventive effect on the sudden death syndrome.
Cobalt oral supplementation can be provided in the form of cobalt ruminal pellets, cobalt in drinking water, cobalt loose licks and blocks and cobalt drenches. Pasture spraying with cobalt sulphate in the autumn should be considered as another preventative alternative to manage the risk of phalaris staggers on high risk pastures.
Clinical signs and diagnosis
It usually takes a minimum of 10 days grazing on phalaris for staggers signs to occur. Most cases occur after one to two months of grazing. Deaths are reported to continue for 1 week after removal from the pasture. Phalaris is well known to cause delayed onset clinical signs, nervous signs can persist for 2 months and have been known to arise up to five months after stock are moved off phalaris. In some animals signs may persist for life but some mildly affected animals will recover. The chance of recovery is higher the more rapid the onset of signs.
Characteristic signs are head nodding and bunny hopping with a wide based gait. Some cases walk on their knees, or knuckle at the fetlocks. Symptoms of staggers can be induced by normal mustering stress. 'Phalaris staggers' can progress to death via the alkaloid affects on the heart causing a heart attack.
There is currently no cure.
Tongue and swallowing paresis particularly in cattle can lead to "manic" attempts to eat with frenzied tongue stabbing at grass.
Characteristic pigmentation in the brain can be seen on microscopic examination at post mortem, and can often also be seen grossly.
It is not really possible to assess the phalaris staggers risk by taking samples from the plants, animals or soil. However known higher risk pastures (from a past history of problems) could be monitored more carefully for seasonal effects and animals grazing these pastures routinely protected by using a supplement.
The risk of stock developing phalaris staggers is a function of soil cobalt levels, levels of soil ingestion and levels of phalaris dominance and palatability. Cases can occur at all times of the year but peak in late autumn and winter. Phalaris has been found to be most toxic during rapid growth (autumn) and then increase again when the plant is placed under environmental stress (such as frost or water stress). The highest concentrations of alkaloids are in the first re-growth and in the leaf blades. Under field conditions, studies have found that the hazard from phalaris decreases as the plant matures. However, this may be because other species dilute the phalaris and because clovers and other legumes contain more cobalt.
Intraruminal Cobalt pellets, given using a 'bulleting gun' are best for long term prevention of staggers and deficiency. In sheep, pelleting is best done when lambs are weaned. Pellets are not suitable for lambs less than eight weeks old. One pellet appears to be enough in most cases, but often two are recommended especially in higher risk situations. Sheep should be treated once every three years, and cattle once a year.
Cobalt bullets for sheep are around $1.40 per head, Cobalt bullets for cattle are around $4.50 per head.
Cobalt in loose licks and blocks
Cobalt sulphate or Cobalt carbonate can be added to drinking water, incorporated into salt licks or mixed with feed. The main problem with intake from licks and blocks is the variation in uptake/usage by individual animals. The recommended supplementation rate to protect against staggers is 28mg Cobalt per week or 4 milligrams/day. To prevent phalaris staggers the rate of cobalt recommended is much higher than usual so many of the nutritional supplement licks would need to be fortified to make them work. Supplementation at the phalaris staggers prevention rate should not be continued longer than necessary.
Cobalt can also be toxic in excess. Cobalt toxicity: daily doses above 4mg/kg bodyweight for sheep and 1mg/kg body weight for cattle would result in toxicity resulting in loss of appetite and depression and doses in excess of 40mg/kg of body weight may result in sudden death.
Cobalt sulphate drenches are available, however the protective effect only lasts about 1 week, demanding weekly re-dosing.
Cobalt Foliar spraying of Phalaris pasture
Annual foliar spraying of phalaris pastures with cobalt soon after the autumn break has reportedly been effective at preventing phalaris staggers in the South East of SA, a region with a high incidence of phalaris staggers.
Mix 100 grams of cobalt sulphate per ha with water and apply to a quarter of the paddock. This can be done by using strips of spray. Most producers use misters due to convenience, however a boom spray may also be used. The foliar spray is only absorbed by green leaves, so producers may need to wait until a few weeks after the autumn break for phalaris to shoot before they spray. Rain within two to three days of application will wash the cobalt spray off before it can be fully absorbed, so spraying should be carefully timed. Livestock can be introduced into the paddock as soon as spraying is completed.
Vitamin B12 injection
Cases of phalaris staggers do not necessarily indicate cobalt deficiency (Vitamin B12 deficiency). Injection of VitB 12 does not offer any protection against the staggers syndrome or phalaris sudden death.
Summary of Phalaris staggers preventive strategies
Cobalt foliar sprays and cobalt bullets are both effective at preventing phalaris staggers. Cobalt foliar sprays may be easier to apply than cobalt bullets and provide full management flexibility with which stock are selected to graze the at-risk productive phalaris pastures.
For more information on Cobalt foliar spraying please see:
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