Rumex acetosella
This weed is found abundantly in both Islands of New Zealand, on waste land and in open pastures. It grows up to 50cm tall, but usually tends to be close to the ground. Its roots are far spreading and branched. The leaves are lanceolate and the flowers are small and oval, the fruit or nut is small and enclosed by persistent tepals which are usually reddish.
Common sorrel and most of the other 12 species of docks in NZ.
Abundant throughout NZ. Likes open situations on poor soil.
Oxalates are present in sheep sorrel, in the free state as oxalic acid, or more commonly as the soluble sodium, potassium and ammonium salts. Sometimes they are present as calcium oxalate. Free oxalate binds calcium in the blood which can cause hypocalcaemia; the calcium oxalate is then deposited in the kidneys which can cause renal failure.
Mainly sheep. Acute oxalate poisoning has been associated with the grazing of sheep’s sorrel and has occurred when hungry stock have either been placed on sorrel infested paddocks or have been driven where sorrel is an abundant road side plant.
Hypocalcaemia - animals stagger and become recumbent, there is a nasal discharge, muscular spasm develops and breathing becomes difficult. Animals usually die in a coma.
Renal tubular necrosis is usually less acute. Signs are oliguria, depression, vomiting, azotaemia, hyperkalaemia and finally cardiac failure.
Horses, unlike ruminants, have no destructive mechanism for oxalates so that the regular ingestion of oxalate containing plants will cause a serious precipitation of calcium oxalate in the gut, resulting in an overall negative calcium balance. After several weeks or months of grazing oxalate containing plants, horses may develop a nutritional secondary hyperparathyroidism which produces osteodystrophia fibrosa. Horses cannot be reared satisfactorily on oxalate containing pastures.
Sheep - severe pulmonary congestion with copious amounts of froth in the trachea and bronchi. There is a marked hyperaemia of the mucosa of the fore stomachs and intestines. The kidneys are usually swollen and have a pale cortex.
History and clinical signs.
When the animal is seen soon after ingestion decontamination to reduce absorption is recommended. Activated charcoal or limewater (calcium hydroxide) to prevent oxalate absorption may be useful. Calcium borogluconate should be given for hypocalcaemia and iv fluids may be necessary for nephrosis. Calcium borogluconate causes a temporary response in some animals which subsequently relapse and die due to acute renal failure.
Prognosis is good with early treatment but poor if clinical signs are advanced or severe.
Sheep sorrel cannot compete with ryegrass and clover mixtures properly grown. Spraying and reseeding with improved pasture management should reduce the nubers of plants present in pasture to insignificant levels.
Conner H.E. The Poisonous Plants In New Zealand. 1992. GP Publications Ltd, Wellington
Cooper M R, Johnson A W. Poisonous Plants and Fungi in Britan: Animals and Human Poisoning. Her Majesty’s Stationary Office. London. 1998
Parton K, Bruere A.N. and Chambers J.P. Veterinary Clinical Toxicology, 2nd ed. 2001. Veterinary Continuing Education Publication No. 208
Surveillance (1974) 1(1): 14 Oxalate poisoning of sheep.
Surveillance (1975) 2(5): 15 Oxalate poisoning (cattle).
Surveillance (1976) 3(3): 16 Oxalate poisoning (sheep).
Surveillance (1982) 9(3): 25 Oxalate poisoning of ewes.
1 November, 2009
