At least one anecdotal report of a dog dying after ingesting cocoa bean shell mulch is being circulated electronically, drawing attention once again to the question of the material's toxicity.
A byproduct of chocolate production, cocoa bean shells are frequently used for home landscaping. Some dogs find the mulch palatable and ingest varying amounts.
Dr. Steve Hansen, director of the American Society for the Prevention of Cruelty to Animals' Animal Poison Control Center, said that as of late April, no reports of lethal toxicosis from ingesting this mulch have been filed with the center this year. In 2004 and 2005, 16 reports of single exposure to the mulch were received, none resulting in death. It is not a source of high-volume calls, he said.
Early publications report that unprocessed cocoa beans contain approximately 1 percent to 4 percent theobromine and 0.07 percent to 0.36 percent caffeine, but the theobromine content of processed cocoa bean shell mulch reportedly ranges from 0.19 percent to 2.98 percent. Manufacturers now state that current processing technology results in lower chemical residues. Dogs are known to be sensitive to theobromine and caffeine—chemicals that are called methylxanthines.
Dogs that consume cocoa bean shell mulch might develop signs consistent with methylxanthine toxicosis, according to a retrospective study of case data collected by the poison control center from January 2002 to April 2003. These signs are similar to those seen in chocolate poisonings. The study by Dr. Hansen and his co-investigators was presented at the North American Congress of Clinical Toxicology and an abstract was published in Clin Tox 2003;41:5. The abstract is posted on the ASPCA Web site at www.aspca.org; search under "cocoa bean mulch" and click on ASPCA:Programs:Animal Poison Control Center:Publications:Cocoa Bean Mulch.
Vomiting and muscle tremors were the most common signs of toxicosis that occurred following ingestion. Anecdotal evidence suggests that the severity of clinical signs increased when larger amounts were ingested. Other signs were tachycardia, hyperactivity, and diarrhea.
The story being circulated about a young dog named Calypso ingesting cocoa bean shell mulch may be true, Dr. Hansen said, but the cause of the dog's death is "highly suspect." The statement that she vomited a few times is consistent with such poisoning, but not the absence of other clinical signs until the next day, when the dog is said to have had a single seizure during her morning walk and died instantly.
"A big problem from the perspective of a toxicologist and a veterinary clinician is that if you have poisoning from methylxanthines, you get a progression of signs—vomiting, diarrhea, more vomiting, trembling, the heart rate kicks up, then it may progress to seizures if the dose is exceptionally high, with death being uncommon," Dr. Hansen said. "A necropsy would have likely shown that Calypso had an underlying condition that caused her death."
Dr. Hansen recommends that pet owners avoid use of cocoa bean shell mulch in landscaping accessible to unsupervised dogs, or at least use it cautiously around dogs with indiscriminate eating habits. The odds of dogs dying from eating the fresh mulch are low, but those suspected of ingesting it should be examined by a veterinarian.