Onion toxicity in farmed animals

Onion toxicity in farmed animals
Peer reviewed

Abstract

Feeding cull onions (Allium cepa) to livestock is practised in onion growing regions around the world. While sheep are able to tolerate onions in their diet, cattle are susceptible to toxicity. Onion poisoning has recently been reported in dairy cows in New Zealand (Carbery, 1999). Given the recent seasonal abundance of onions available for feeding to stock, it seems timely to draw attention to this syndrome. Onions are known to be toxic to many species including humans, cattle, horses, sheep, goats, dogs and cats. Recent studies have shown that more than one toxin is involved. Onions and other plants of the Allium family, such as garlic and leeks, contain n-propyl disulphide, and S-methyl and S-propenylcysteine sulphoxides (SMCO and SPCO) that may be broken down into various sulphides. SMCO and SPCO have a stronger haemolytic capability than n-propyl disulphide. However, all three disulphides have been associated with methaemoglobinaemia and haemolytic anaemia with Heinz body formation. Animals given free access to onions with other feed sources may prefer the onions and ingest toxic amounts. The severity of toxicosis depends on the animal species and the quantity of onions ingested. Not all onions contain the same amounts of n-propyl disulphide, SPCO and SMCO. Mild varieties of onions probably contain lower levels of disulphides, as flavour, pungency and odour are associated with the amount of SMCO and SPCO and their degradation products contained. Livestock species most susceptible to poisoning, in decreasing order are…

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