Page 145 - Raw Diet References Book 2019

7.3 Toxicity of onions and garlic in cats & dogs

7.3.1 Background

It has been known since 1930 that dogs are very or dehydrated.
sensitive to onions (Allium spp) whether raw, cooked

7.3.2 Clinical signs and pathology

Regenerative anaemia with marked Heinz body signs with the onion ingestion because of the lag of
formation has been reported in cats and dogs after several days before the onset of clinical signs (Weiser
eating onions or onion containing foods (Harvey et 1995, Cope 2005).
al. 1985, Kaplan 1995, Robertson et al. 1998, Spice
1976, Tvedten et al. 1996). Consumption of a sufficient Although onion poisoning is more common in dogs,
amount of onions leads to oxidative injury of the cats are more sensitive to onion and garlic poisoning
lipid membrane of the erythrocytes and irreversible owing to their specific haemoglobin structure, making
oxidative denaturation of haemoglobin. This results in them more susceptible to oxidative stress (Giger 2000).
formation of Heinz bodies, eccentrocytes (red blood
cells with haemoglobin clustering at one side of the Garlic and Chinese chives have also been reported to
cell, which makes these cells more susceptible to lysis cause the development of Heinz bodies, eccentrocytes,
than normal red blood cells), haemolytic anaemia, haemolytic anaemia and increases in methaemoglobin
haemoglobinuria, increased serum bilirubin and levels in dogs (Lee et al. 2000, Yamato et al. 2005). Lee
possibly methaemoglobinaemia (Faliu 1991, Cope et al. reported toxic effects after administration 1.25ml
2005, Harvey et al. 1985, Kaplan 1995, Lee et al. 2000, of garlic extract per kg BW (equivalent to 5g/kg BW of
Robertson et al. 1998, Means 2002). Relatively small whole garlic) for 7 days, this is similar to the amounts
amounts of fresh onions (5 to 10g/kg BW) can already reported in onion poisoning.
be toxic (Faliu 1991, Cope 2005). Robertson et al. 1998
showed that effect was dose dependent. The increase in reduced glutathione (G-SH), which
has been reported after ingestion of onions and garlic,
The clinical signs are secondary to the anaemia may seem inconsistent with oxidative damage, but the
and include pale mucous membranes, tachycardia, increase can be a compensatory rebound reaction after
tachypnoea, lethargy and weakness (Gfeller & Messonier an initial decrease in G-SH and other body anti-oxidants,
1998, Cope 2005). Vomiting, diarrhoea and abdominal and an increase in oxidised glutathione (GSSG) within
pain may also be present. If only a moderate amount of the first few days (Yamoto 1992, Ogawa et al. 1986).
onions has been eaten, the Heinz body anaemia resolves
spontaneously after discontinuing the onions (Kaplan Dogs with hereditary high erythrocyte concentrations
1995, Robertson et al. 1998). In more severe cases, of reduced glutathione and potassium appear to be
icterus and renal failure can be seen as a consequence more sensitive to onion and garlic poisoning (Yamato et
of the haemolysis and haemoglobinuria respectively, al. 1992).
and possibly death (Ogawa et al. 1986, Cope 2005).
Wild onions (A. validum & A. Canadense) and wild garlic
Although onion ingestion has been reported as being (A. ursinum) have caused haemolytic anaemia in horses
the most common cause of Heinz body haemolysis in and ruminants (Lee et al. 2000) and are potentially toxic
dogs (Weiser 1995), it may be difficult to correlate clinical for dogs and cats as well.

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