CASE NOTES


Oxalate Toxicity

Paul Freeman, District Veterinarian, Casino RLPB

Posted Flock & Herd February 2011

There are two main categories of poisoning due to oxalates in plant

1. Soluble oxalates

Species affected

Sheep, cattle

Sources

A wide variety of plants can contain high concentrations of soluble oxalates mainly as the potassium salt.

Plants - sorrel, dock, soursob, pigweed
Tropical grasses - Setaria, buffel grass, panics

Risk Factors

Pathogenesis

Within the rumen soluble oxalates can either be absorbed intact or form insoluble complexes with calcium which can either be shed in the faeces or lodge in the rumen wall where they may cause a chemical rumenitis.

When soluble oxalates are absorbed into the blood stream they bind strongly with calcium forming insoluble calcium oxalates.

Some of there complexes can cause vascular damage and some pass to the kidneys and are either passed in the urine or lodge in renal tubules causing damage. High circulating levels of soluble oxalates can also cause pulmonary oedema.

Symptoms

Diagnosis

Treatment

Calcium parenterally

Prognosis

Poor if recumbent for over 24 hours or if renal damage has occurred.

2. Insoluble oxalates

Species

Horses and donkeys.

Risk factors

Grazing pure or near pure swards of tropical grasses with high levels of insoluble oxalates as the druse or prismatic crystal formation.

Pathogenesis

Calcium absorption in horses occurs mainly in the duodenum and calcium oxalate crystals in horses are broken down in the large intestine with the calcium released from degradation primarily excreted in the faeces. The resulting calcium deficiency results in excess parathormone and mobilization of calcium from bones to maintain blood Ca levels.

This leads to osteodystrophy.

Symptoms

Shifting lameness, stiffness, weight loss
Swelling of mandible and/or maxilla (‘bighead’)

Treatment

Add mineral mix with Ca: P ratio of 2:1 for about 3-6 months

Remove from at risk pasture

Prevention

Intermittent grazing on at risk pastures

Supplementary mineral mix at half therapeutic doses.

Species affected
Herbivores
Young dogs and cats

Caused by irritation of buccal mucosa by Calcium oxalate crystals in the ‘raphides’ form

These crystals are present in a small number of plants species (monsterio delicio, cunjevois, umbrella trees, philodendron, arum lily )

Case histories of Oxalate poisoning in cattle on Setaria

Setaria is an African origin tropical grass that is widely used on the north coast because of its productivity and persistence in wet conditions. It produces a large biomass and thrives in a wide variety of soil types.

Case # 1

70 cow dairy herd with 7 cows recumbent after 3 hours grazing on Setaria that had last been fertilized 6 weeks previously.

The cows had been grazing ‘Poona peas’ for 3 days prior to being placed on the Setaria.

The outcome was that 2 cows died and 5 recovered after treatment with calcium parenterally.

Case # 2

80 cow dairy herd with 2 cows dead after 24 hours grazing on recently fertilized Setaria.

The cows had been grazing Lucerne prior to being on the Setaria.

Comment

References

Mckenzie R., 2002. Toxicology for Australian veterinarians: plant toxins — oxalates pp 28-46. CD available from the author

 


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