Beetroot is mainly cultivated for human consumption, while Goosefoot occurs as a weed in disturbed places. Spinach mostly cultivated for human consumption. Low grade quality sometimes used as a stock feed.
Vegetables that are planted primarily for human consumption. The seedlings of C. album look woolly on the upper side and are usually purple underneath. Under certain growing conditions the centres of young plants are are bright purple. The young leaves have a waxy coating.
Can contain oxalates (as well as nitrates/nitrites) in dangerous concentrations. Depends on fertilization, growth stage, etc.
Nitrate / Nitrite.
MECHANISM OF ACTION:
In the rumen nitrate is reduced to nitrite and following absorption haemoglobin is oxidised to methaemoglobin.
• Great variations both inter- and intraspecies
• Nitrate - c. 0,5 g/kg sheep - 5g/kg cattle
• Nitrite - c. 20 mg/kg sheep - 100mg/kg cattle.
Haemopoietic and urogenital systems.
Urogenital acute poisoning:
• Hypocalcaemia phase: -soon after intake, 2-6 hours
- Paresis to paralysis, semi-comatose, “milk fever” signs
- Head thrown back onto shoulder
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.
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.
Kidney- and bladder stones where oxalates can play a role amongst other things.
Haemopoietic acute poisoning:
• Respiratory System:
- anoxia precipitated by exercise.
• Cardiovascular System:
- cardiovascular failure,
- methaemoglobinaemia: blood & mucous membranes a dirty chocolate
- Rapid weak pulse (drop in blood pressure)
• Central Nervous System:
- terminal convulsions (brain anoxia)
• Gastrointestinal Tract:
- salivation (vomition)
• Abortion - especially last trimester.
Urogenital Macroscopical findings:
- Nothing significant,
• 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.
Typical oxalate crystals in kidney tubules (seen under polarized light) with signs of kidney damage.
Haemopoietic macroscopical findings:
• Tarry, dark, red-brown to brown blood• Tissues and mucous membranes brown (Not apparent in every case)
• Petechial and ecchymotic haemorrhages on mucosal, visceral and serosal surfaces
• Nothing unusual or pathognomonic.
Urogenital Treatment of little value - irreversible condition.
• 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 feeding.
1. Methylene blue. Acts as intermediate electron acceptor that accelerates the reaction between NADPH and methaemoglobin.
2. Ascorbic acid. Also used in dogs for paracetamol poisoning.
Colour photos. Final web-ready size: JPEG, 72 ppi. Photo 1: 64 kb; Photo 2: 9.7 kb; Photo 3: 27.5 kb; Photo 4: 36.4 kb. Original TIFF file housed at the Dept. of Paraclinical Sciences, Section Pharmacology and Toxicology, University of Pretoria.