DISTRIBUTION:
Originally from central Mexico, it is now to be found mostly in the drier regions of the country, along the coast, etc. Also cultivated as garden subjects and for drought feeding.
Botanical description: General: Prickly pear is a branching shrub or tree with fleshy leaf-pads that are flattened, 1 - 3 cm thick, varying from heavy spined to spineless.
Flowers: During November plants are covered with bright yellow to orange flowers that grow from the margins of the leaf-pads.
Fruit: The succulent edible fruits are yellowish when ripe. They are covered with clusters of tiny spines.
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.
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.
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.
