Oxalis species

Abstract

DISTRIBUTION: Widely distributed. Growing on nearly all soil types and under most climatic conditions. More than 200 species are found in South Africa; only two are exotic. Mostly in damp conditions in high rainfall areas. Often found as weeds in gardens.

BOTANICAL DESCRIPTION: General: Annual or perennial herbs, sometimes stemless, often with “corms”, underground stems or stolons or fleshy taproots. Often in small colonies. Leaves: The leaves are usually trifoliate, but can be simple. Photosensitive (folding back at night like butterfly wings). Flowers: Bell-shaped flowers in clusters on long slender stalks. Flowers can be in shades of white, pink, red or yellow.

TOXIC PRINCIPLE: Contains soluble oxalates.

SYNDROMES: Soluble oxalate poisoning, Primary nephropathy.

SYSTEMS AFFECTED: Urogenital system.

CLINICAL SIGNS: Acute poisoning: • Hypocalcaemia phase: -soon after intake, 2-6 hours - Weakness - Paresis to paralysis, semi-comatose, “milk fever” signs. - Head thrown back onto shoulder - Bradycardia - Mortalities Treatment of these symptoms with Ca-borogluconate gives good results and animals may recover. • Kidney failure phase: Following day to few days later due to blockage and damage of tubuli by Ca-oxalate crystals resulting in: - Uraemia: BUN and creatinine increase - Oliguria or anuria Treatment of very little value - irreversible condition.

NECROPSY: Macroscopical findings: • Hypocalcaemia: - Nothing significant, - haemorrhages. • Nephrosis and Uraemia: - Ascites, hydrothorax, perirenal and subcutaneous oedema. - Kidneys pale, oedematous, swollen - nephrosis. - Ammonia and urea odour (uraemia). - Haemorrhages in different organs. - Oedema and haemorrhages in rumen.

HISTOPATHOLOGY: Typical oxalate crystals in kidney tubules (seen under polarized light) with signs of kidney damage.

TREATMENT: CONTROL: • Avoid sudden exposure to oxalate containing plants or intake of large quantities. • Avoid oxalate containing plants as the only food. • Feed Ca2+ in the form of dicalcium phosphate as a lick (25% or more with salt) or mixed in the supplementary feed.

EPIDEMIOLOGY: • Acute poisoning happens where: - unadapted animals suddenly eat a relatively large amount of oxalate containing plants and the oxalates are absorbed into the circulation - excessive large amounts of oxalates are absorbed in adapted animals which are not able to detoxify all the oxalates in the rumen (e.g. large amounts during droughts). • Chronic effect characterized by: Calcium deficiency resulting in: - bone abnormality, - poor milk production and - poor growth. N.B. Kidney- and bladder stones where oxalates can play a role amongst other things.