Oxalate poisoning

OXALATE POISIONING

Plants contaning oxalates

  • Oxalates poisoning is of great concern in livestock and human beings all over the world.
  • Oxalic acid is an organic dicarboxylic acid that readily forms insoluble salts with cations like calcium and magnesium.
  • However, its sodium, potassium or ammonium salts are highly soluble and can induce toxicity in animals.

Sources of poisoning

  • Oxalate poisoning in livestock primarily results from ingestions of large quantities of oxalate containing plants.
  • Oxalate containing plants are palatable and frequently form bulk of ruminant’s ration.
  • For causing toxicity, the plants should contain more than 10% oxalic acid on dry-weight basis. The form in which oxalate is present in the plant may be of importance in terms of toxicity, that is whether it exists mainly as acid oxalate (e.g. in Oxalis sp. Rumex sp.) or oxalate ion (e.g. in certain Chenopodiacae).
  • Some of the common oxalate containing plants are listed in Table.

Table: Some of the important oxalate containing plants

Amaranthus retroflexus

Rheum rhaponticum

Atriplex sp.

Rumex sp.

Beta vulgaris (beet)

Sarcpbatis vermicularis (Grease wood)

Brassica hyssopifolia

Spinacia aleracea (Spinach)

Calandrinia sp.

Salsola kali sp.

Chenopodium album

Setaria sphacelata

Halogeton glomeratus

Threlkeldia proceriflora

Oxalis sp.

Trianthema sp.

Portulaca sp.

Mechanism of toxicity

  • Normally after ingestion of the plants, calcium present in the stomach may react with the oxalates to form insoluble salts which can not be absorbed and eliminated in the faeces.
  • This process is more effective in ruminants than simple stomach animals and consequently, ruminants can consume large amounts of oxalate containing plants without any apparent signs of toxicity.
  • However, when very large quantities are ingested that exceeds and capacity of digestive tract to convert the soluble oxalates into calcium oxalate, the soluble oxalates get absorbed through intestinal mucosa and are available to interact with blood calcium causing acute hypocalcemia.
  • Further, calcium oxalate crystals may get accumulated in the kidney tubules causing severe renal damage.
  • Calcium oxalate may also crystallize in the brain.

Clinical signs

  • Dullness, lowering of the head, loss of appetite and remaining isolated from the herd are initial evidences of oxalate poisoning seen after 4 hours of feeding oxalates-rich plants.
  • These observations are followed by excessive salivation with frothing, progressive incoorrdination and coma with deep irregular respiration. Convulsive episodes may also be noted.

Post-mortem lesions

  • Lungs may be filled with dark-red or purplish coloured blood as most of the deaths in oxalate poisoning are associated with asphyxia.
  • Petechiael haemorrhages and cyanosis may be seen at various location.
  • Crystalline masses may be observed in renal tubules, with a concentration in the cortices.
  • Microscopic examination of kidneys may reveal presence of calcium oxalate crystals, ruptured tubules and degenerative changes.

Diagnosis

  • History of feeding / grazing on oxalates-rich plants
  • Clinical signs
  • Post-mortem lesions.
Last modified: Friday, 23 March 2012, 9:00 AM