CASE NOTES


THE ROLE OF COBALT IN THE RISK ASSESSMENT AND PREVENTION OF PHALARIS STAGGERS

David Rendell, Livestock Intel, 60 Portland Rd Hamilton 3300

Email: d.rendell@livestockintel.com.au

Posted Flock & Herd September 2012

INTRODUCTION

Phalaris staggers is an incoordination syndrome that is associated with the ingestion of phalaris (Phalaris aquatica) which contains dimethyltryptamine alkaloids (Finnie et al 2011).

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. Cattle are less susceptible than sheep but when they are affected it causes a larger problem. Phalaris staggers affect the nerves that control prehension of food and swallowing, so affected cattle are unable to eat normally and suffer a high degree of weight loss. Symptoms of staggers can be induced by normal mustering stress up to two months after leaving a phalaris paddock. There is currently no cure.

Oral cobalt is commonly used as a preventative agent against phalaris staggers (Radostits 2007). Preventative levels of dietary cobalt in sheep are double those required to maintain adequate levels of Vitamin B12 in blood. Therefore, cases of phalaris staggers do not necessarily indicate Vitamin B12 deficiency.

'Phalaris staggers' is a completely separate syndrome to 'phalaris acute sudden death'. The sudden death syndrome is proposed to occur as a result of ingesting of a compound in phalaris that decreases nitrogen metabolism, resulting in peracute ammonia poisoning (Bourke 2005). The sudden death syndrome occurs in autumn to early winter within 36 hours of introducing stock onto phalaris pastures. It takes sheep 24 hours to develop effective nitrogen metabolism on phalaris. If affected sheep are found alive still able to stand unassisted, and are treated with 200 ml of vinegar orally, the recovery rate is around 75%. Cobalt has no preventive effect on this sudden death syndrome.

CLINICAL SIGNS & DIAGNOSIS

It takes a minimum of 10 days grazing on phalaris for staggers signs to occur. Most cases occur after one to two months of grazing. Signs can arise up to two months after stock are moved off phalaris. Signs usually persist for life. 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. (see video that demonstrates signs to look for.)

staggersClick
Click to play video

Tongue and swallowing paresis particularly in cattle can lead to "manic" attempts to eat with frenzied tongue stabbing at grass ( see video of affected cow)

Characteristic pigmentation in the brain can be seen on microscopic examination at post mortem, and can often also be seen grossly.

Cases between 18 months and five years are likely to be eligible for the TSE surveillance subsidy. This provides $50 to the farmer and covers the post mortem costs.

ASSESSING RISK

Animal Cobalt/B12 tests (blood or liver tests)

As phalaris staggers can occur in animals with normal vitamin B12 levels, B12 blood levels are not reliable in predicting the risk for developing staggers. There are also reports that tests for vitamin B12 blood levels in cattle are unreliable at determining B12 deficiencies (Judson pers. comm 2012).

The author is not aware of any information correlating liver vitamin B12 concentrations with level of risk.

Mapping Underlying Parent Rock of Paddock Soil

The main source of cobalt on phalaris dominant pastures during autumn and winter is ingested soil. The parent rock is the major determinant of soil cobalt levels: ranking parent rock from lowest to highest cobalt levels, risk is as follows:

Limestone has the highest risk for low cobalt hence the high risk of phalaris staggers in the south east of South Australia. This also might explain why high pH soils are regarded as higher risk for low cobalt. Sandstone is the next highest. Granite poses an intermediate risk. Basalt poses a low risk. The risk posed by alluvial soil varies with its parent rock type soil. Conglomerate rocks vary depending on the proportion of rock types of which they are made up.

Soil Cobalt Tests

Conducting soil tests is not recommended, as there is no calibrated standard or reliable method for measuring soil cobalt available in the published literature. However, with further trials/research this may be a useful method.

Plant Tissue Tests

Phalaris has very low uptake of cobalt from all soils, therefore tissue tests of phalaris will not assist in predicting at risk paddocks . Legumes have much higher levels of cobalt and hence risk of staggers diminishes when the proportion of legumes in pasture increases.

SUMMARY OF ASSESSING RISK OF PHALARIS STAGGERS

Risk assessment involves the collation of several factors. These include knowledge of previous staggers cases in individual paddocks, grazing palatable phalaris dominant pastures with low legume content, likely levels of soil ingestion and the underlying parent rock of each paddock. Such assessment will assist in prioritising at risk areas.

PREVENTION OF PHALARIS STAGGERS

Cobalt Foliar Spraying of Phalaris Pasture

Background

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 (McFarlane pers. comm 2012). Cobalt foliar sprayed pasture was found to raise the vitamin B12 blood levels of sheep from deficient to normal levels for a few months in an unpublished trial (McFarlane pers. comm 2012). A client of the author based on a large sheep property west of Naracoorte advised that the only year that they were affected by phalaris staggers occurred after the manager forgot to apply cobalt spray, and involved 20% losses in a mob of mature first cross ewes.

Application Recommendations (J. McFarlane pers. com. June 2012)

Mix 100 grams of cobalt sulphate per ha with water and apply to a quarter of the paddock. 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.

Cost of Cobalt Foliar Sprays

In 2011 the cost was around $30 per kg (not including GST); the minimum sized bag of 25kg cost $825. The chemical cost was around 75c per Ha. As only a quarter of the paddock was sprayed and the cobalt was of low toxicity, drift was not a problem. Therefore, tractors could travel at a fast rate over the quarter of the paddock that was easiest to traverse over. Contractor rates were $12 - 17 per Ha but only spraying ¼ of paddock = $3-4 /ha. Total spraying costs were thus around $4 per Ha.

Cobalt Bullets

Over fifty years ago the CSIRO demonstrated that the administration of two oral cobalt slow release bullets to sheep would prevent the onset of phalaris staggers for three years. Chris Bourke, NSW DPI, prefers the use of two cobalt capsules per head. Sheep should be treated once every three years, and cattle once a year. Bullets ensure that sheep are treated all year round for cobalt deficiency, rather than only when grazing pasture that has been sprayed in the previous few months. This prevents cobalt levels declining to marginal levels, which is a risk factor for a significant outbreak of phalaris staggers.

Properties in the Hamilton district of Victoria that have only had occasional problems with phalaris staggers have found that one cobalt bullet has been effective at preventing phalaris staggers. However, in 2012 one property in the Melville Forrest district had substantial phalaris staggers in a mob that had been given a single bullet only two years earlier. So whilst one bullet appears to be enough, two bullets is safer, particularly in the third year.

Cost of Cobalt Bullets

Cobalt bullets are around $1 per head, and administration and mustering would cost around 20 c per head for 3 years protection: Single bullet = $1.20 per head, two bullets $2.20. If running around 10 sheep per ha = $3-4 per Ha per year single bullet ($5-7 double bullet).

Vitamin B12 Injection

This is cheap at 8c per dose and gives an immediate boost to animal vitamin B12 levels lasting 6 - 12 weeks. It does not prevent or have any beneficial treatment effect on phalaris staggers 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 are easier to apply than cobalt bullets and provide full management flexibility with which stock are selected to graze the at-risk productive phalaris pastures.

There is no effective treatment for affected sheep. Sheep with advanced signs must be promptly euthanased.

REFERENCES

  1. I Judson (2012), personal communication
  2. Jock McFarlane (2012), agronomist at Struan Naracoorte Department of Primary Industry SA, personal communication
  3. Bourke, C, Colegate, S, Rendell, D, Bunker, E & Kuhn, R (2005), 'Peracute ammonia toxicity: A consideration in the pathogenesis of Phalaris aquatica 'Polioencephalomalacia-like sudden death'poisoning of sheep and cattle, Australian Veterinary Journal, vol. 83, no. 3, pp. 168-171
  4. Finnie, JW, Windsor, P & Kessell, AE (2011), 'Neurological diseases of ruminant livestock in Australia. II: toxic disorders and nutritional deficiencies', Australian Veterinary Journal, vol. 89, no. 7, pp. 247-253
  5. Radostits, O (ed.) (2007). Veterinary Medicine: A textbook of the diseases of cattle, horses, sheep, pigs and goats, Edinburgh: Elselvier

 


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