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Local Vets since 1949

Toxicology

Pyrrolizadine Alkaloids

Pyrolizidine alkaloids, found in blue heliotrops, are a common plant toxin found in our area and cattle may be forced to feed on toxic plants in drought condition. They exert their toxic effect in cells of the liver (lung and kidney) by inhibiting cell division. Large non functioning cells develop in the liver (megalocytes) which can then inhibit the organs ability to function properly.  Mortalities are likely to develop after a few weeks of exposure. Mild diarrhea, abdominal straining followed by anorexia, depression, weakness and ataxia can develop after eating plants containing this compound. Jaundice and bottle jaw may develop at the end stages of this disease.

In horses, this disease is known as ‘walkabout disease’, named after the effect the liver changes and high ammonia blood levels have on the brain of the horse causing them to walk aimlessly, colliding with objects in their path as if they were blind.  There is no know effective cure for this disease and generally the horse progressively deteriorates. Preventing access to known poisonous plants (Crotalaria spp.) is to be encouraged.

Nitrates

Nitrates in the diet of livestock (oats, corn, sorghum, barley, wheat) can be converted in the rumen to nitrite and then ammonia. Nitrite can rapidly oxidize oxyhaemoglobin (carries oxygen in the blood stream) to methaemoglobin (unable transport oxygen) and when the levels reach above 20% in the bloodstream, tissue anoxia results leading to cell death and clinical signs. Cattle will become short of breath, they develop a dull colour in their mucous membranes and their blood will appear quite brown (chocolate coloured). They may have muscle tremors, weakness and lie down. At high methaemoglobin levels (80%) cattle usually die.

Treatment if given early can be successful. The methaemoglobin can be reversed with methylene blue given into the vein of affected cattle. A long with holding period on the milk and meat usually is required following treatment.

Cyanogenic Glycoside

Prussic acid or cyanide poisoning (HCN) can develop in cattle when feeding grain sorghum. Seen mainly during summer, HCN can be released in the rumen from the plant to inhibit the cellular processes which allow tissues to use oxygen properly. Tissues are starved of oxygen and die. Acute cyanide poisoning is characterised by rapid, deep breathing, irregular weak heart rate, salivation, muscle spasms and death. The clinical signs seen early usually include the appearance of bright red coloured blood due to the high levels of oxyhaemoglobin in the circulation. The amount of cyanide found in plants can vary if the improved pasture is stressed with inclement weather.

Treatment if given early can be successful.  Therapy usually requires the use of sodium nitrite to convert blood to methaemoglobin which acts as a sink for the cyanide. Cyanomethaemoglobin can then be broken down by simultaneously treating the animal with sodium thiosulphate (Hypo) orally.

Botulism

Botulism is a disease caused by the botulinum toxin. It is commonly seen in the phosphorus deficient areas of northern Australia, however, reports of botulism have become more frequent in parts of Queensland. Most of these outbreaks have been in intensively fed beef and dairy cattle. Botulinum toxin is often reported as being one of the most potent toxins known to mankind, as only a small quantity is required to produce disease. The toxin binds strongly to nerve endings, preventing nerve impulses proceeding to muscles. This leads to the type of paralysis typically seen with botulism where animals go floppy or flaccid because they cannot move their muscles.

Botulism symptoms

  • sudden deaths (animals collapse and die in a couple of hours)
  • a slowly progressive paralysis where animals may take days to die
  • a wobbly gait (staggers)
  • aggressive behaviour
  • difficulty breathing
  • tongue paralysis

Toxin in the water

Cattle can tolerate poor water quality better than humans, but if concentrations of specific compounds found in water are high enough, cattle can be affected. Most factors affecting water quality are not fatal to cattle. Cattle may not show clinical signs of illness, but growth, lactation and reproduction may be affected, causing an economic loss to the producer.

Most common water quality problems associated with surface water are:

  • Blue-green algae (cyanobacteria)
  • Bacteria, viruses and parasites
  • Sulphates
  • Dissolved solids (TDS)

Toxins in feed

The usual sources of toxin in intensively fed cattle are feedstuffs contaminated with rotting animal or vegetable material. Sources of rotting material in stored feed have included:

  • Dead snakes and possums in grain augers.
  • Snakes and other animals in hay and silage.
  • Mice when mouse plagues result in large numbers of mice dying in stored feedstuffs and in grain augers, especially at the end of a plague.
  • Water may also be a source of toxin if animals that die in dams, tanks or troughs are left to decompose.