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This article was published in 1977
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Blue Green Algae Toxicity in Sheep and Cattle
R.I. Walker, B.V.Sc., Veterinary Inspector, Young
Introduction
There are at least two species of algae belonging to the Cyanophyta (Blue-Green algae) which are responsible for acute poisoning and mortalities in sheep, cattle, horses, native birds, honey bees and mice under laboratory conditions.
These are Anacystis cyanea (syn. Microcystis aeruginosa) and Anabaena circinalis. They are both found in standing or sluggish water, but it seems that only particular strains are highly toxic and that toxicity may only be related with certain stages of growth in these strains.
It has been known for some time that strains of Anacystis cyanea produce a highly potent toxin, but only recently has a similarly potent toxin been demonstrated for Anabaena circinalis.
It can be anticipated that with a wider level of pollution these two algae are likely to be seen more frequently and stock poisoning therefrom may be a more common diagnosis.
Algae Characteristics
Anacystis cyanea is a planktonic algae of still or sluggish fresh water, often occurring was a waterbloom (sic). A sample of infested water, when shaken, resembles green paint, but on standing a bright emerald green scum forms on the top of a layer of clear or turbid water. A blue-grey sediment may form on the bottom of the collection jar after some time. On microscopic examination the alga is seen to form colonies of small cells, packed closely in a mucilaginous substrate. Individual cells are approximately 3-7ยต in diameter. Multiplication takes place by fragmentation.
An almost identical description can be given for Anabaena circinalis. The growth however consists of trichomes, whose cell are spherical or barrel-shaped, and contain gas vacuoles. These gas vacuoles give both the algae buoyancy.
Both algae liberate a very pungent, acrid odour similar to the product known as Gammexane (Gamma isomer of benzone hexachloride). This may only appear at certain stages of growth.
Both algae may occur individually or together and can form very dense blooms, which form immediately below the surface of the water. They are both subject to a prevailing wind and this is important in regard to anticipating or diagnosing poisoning. They may also appear and disappear quite rapidly over a matter of days.
These algae are found chiefly in the Central and South Western Slopes regions during the summer and autumn months. Toxic blooms may be more likely to appear when drought conditions prevail and when alternate sources of water are non-existent.
The level of phosphorous in the water seems to be critical in the growth of those algae. A level higher than 0.5 ppm (phosphorous) will stimulate growth of the algae. This is related also to a large increase in bacterial numbers in the water and not necessarily associated with any external source. A large population of bacteria produce anaerobic conditions which allow stored phosphorous to be released from polluted mud. Both Anacystis and Anabaena may overwinter in mud or even dry soil and develop when conditions are suitable. Together with phosphorous levels and bacterial numbers, pH appears to control algae growth. Algal blooms have not been recorded where pH is less than 6.
Toxicity in Animals
The fact that algae are present does not necessarily indicate a risk to stock as poisonous effects depend on strains of the algae, concentration of the toxic principle, stage of growth, presence of bacteria, the size of the bloom and the susceptibility of the animals, as well as wind direction (and) placing the algae where stock have no alternative source of water.
a). SHEEP - most reports involving sheep give Anacystic cyanea. as the most common agent.
Mortality rates in the order of 2-10% give an indication of the magnitude of the poisoning. It may only take 5-10 days of watering on infested water before deaths are observed. Young animals appear more greatly at risk.
With Anabaena circinalis, only one case of deaths in sheep have been attributed to it, and in that case in Young in 1974, 20/500 10 month old Corriedale lambs were found dead after watering on a dam infested with this species.
b). CATTLE - reports overseas indicate cattle deaths are common with the algae (Anacystis). Again, in Young in 1976, 5/60 7-8 month old Shorthorn vealer calves died and Anacystis cyanea was incriminated.
c). HONEY BEES - An almost total mortality within 48 hours was reported at Finley in December 1971, in 84 hives, where bees were watering on an infested portion of Lake Uranagong. Anabaena circinalis was recovered in almost pure form in this case.
d). LABORATORY MICE - The toxin produced by both algae is lethal to mice and forms the basis for standard mouse toxicity tests in the laboratory. There appear to be quick death factors (probably purely algae) and slow death factors (probably bacterial) involved and it is surmised that algae and bacteria exist in a symbiotic relationship. The toxin found to date is an endotoxin, a cyclic polypeptide containing D-Serine, which has an LD-100 for mice of 0.2 mg/kg body weight by intraperitoneal injection.
CLINICAL HISTORY
There is usually very little recorded on clinical symptoms as deaths are very rapid, maybe within 1-2 hours, and live, affected animals, are seldom seen. Some adult sheep have been found to show a stagger (possibly similar to Rye Grass staggers) and others have shown depression, without loss of reflex action.
AUTOPSY FINDINGS
While not precisely diagnostic, the following pathological changes have been observed.
Straw coloured fluid in thoracic and abdominal cavities, congestion of lung, liver, mesenteric lymph nodes and vessels, petechial and ecchymotic haemorrhages in subcutaneous tissues of neck and shoulders and in the endocardium and epicardium. Haemorrhages and inflammation have also been observed in abomasal mucosa and in small and large intestine.
Hepatocellular damage with coagulation necrosis is found in the liver but this is irregular in distribution. This damage however may predispose to photosensitisation and jaundice in those animals which survive.
CONTROL
Copper sulphate placed into infested water at 1 ppm by weight has been shown to be partially successful but it is likely that algae may re-appear in 10 days. The algae are common during summer and autumn but usually die out as cool to cold weather commences. Control for the algae may also be dependent on the wind direction and certain paddocks may need to be shut up or the suspect dam fenced off until the algae is controlled.
PREVENTION
Recent research has indicated an alternative method, but involves treatment of water the winter prior to the expected growth in summer. Obviously this applies only in situations where the algae are a continual problem in the one site.
The aim of prevention in this case is to prevent the level of phosphorous reaching 0.5 ppm or above.
Block Ferric Alum (a mixture of hydrated aluminium and ferric oxides), at a rate of 0.25 - 1.0 kg/5000 litres of water, is used by suspending the blocks in terylene bags attached by nylon ropes to floats, and placed strategically around the dam. This forms a flock gel into which the phosphorous is absorbed, thus removing it from suspension.
The ferric alum is replenished as it dissolves (perhaps every second or third month).
Cost has been quoted as $200/5-6000 cu.ft. (i.e. $100/140-170 cu.m.)
It has also been stated that blooms in large reservoirs may be controlled by aeration.
REFERENCES
E.J. McBarron & Valerie May (1966) A.V.J. 42 (12): 449
V. May (1974) J. Aust. Inst. Agric. Sci. 40 (1) : 54
Vet Notes (1975) Vol 11 (2) : 18
Blue Green Algal Booms at Braidwood N.S.W. V. May - Science Bulletin 82., Dept. of Agric. N.S.W.
Maria T.C., Runnegar & I.R. Falconer. Proceedings of Aust. Biochemical Society (1975) Vol. B.: 5
McBarron, Walker, Walker & Gardner (1975) (Anabaena) A.V.J. 51 : 587
May & McBarron, J. Aust. Inst. Agric. Sci. (1973). P266
Agricultural Gazette (1974) Vol. 85 (2) : 45 Research News
Jubb & Kennedy - Pathology of Domestic Animals