Whether processed or fresh, macadamia nuts can cause problems for your pet. Dogs are the only species in which toxicity has been reported.

macadamia nuts

Signs and symptoms of toxicity: weakness, depression, vomiting, lack of muscle control, tremors, joint pain, difficulty walking, hind limb weakness, elevated body temperature, and mild abdominal pain. These signs usually occur within 12 hours of ingestion.

Toxic Consumption: Typically clinical signs of toxicity are seen at > 2 g/kg (0.8 g/lb) . However, as little as 0.7 g/kg (0.3 g/lb) may cause signs of toxicosis.

For all considerations below, an approximation of 12 nuts in 1 ounce of macadamia nuts was used.

Dogs: Macadamia Nut Toxic Consumption
X-Small
Yorkie, Chihuahua
Small
Pug, Boston Terrier, Poodle
Medium
Beagle, Scottish Terrier
Large
Boxer, Cocker Spaniel
X-Large
Retriever, German Shepherd
XX-Large
Great Dane, St. Bernard
1 – 10 lbs.
(0.45 – 4.6 kg)
11 – 25 lbs.
(5 – 11.4 kg)
26 – 40 lbs.
(11.8 – 18.2 kg)
41 – 70 lbs.
(18.6 – 31.8 kg)
71 – 90 lbs.
(32.3 – 40.9 kg)
91 – 110 lbs.
(41.4 – 50 kg)
dog1 dog2 dog3 dog4 dog7 dog6
> 0.1 nuts > 1 nut > 3 nuts > 5 nuts > 9 nuts > 12 nuts

References:
– Osweiler, G, et al. (2011). Blackwell’s five-minute veterinary consult clinical companion. Small Animal Toxicology. [Kindle version]. Retrieved from Amazon.com
– The Merck Veterinary Manual. Macadamia Nuts. Available at: http://www.merckmanuals.com/vet/toxicology/food_hazards/macadamia_nuts.html. Accessed August 31, 2014.