Dogs and Grapes: It?s Not That Simple

 Randy Hayes

The impetus for this article comes from a social media posting I did several months ago indicating that my KBT (Lola) and I were having our afternoon grape break. I received a message from my sister who informed me that according to her vet, grapes were toxic to dogs. I did a quick Google search and found a number of interesting articles on this subject. But the most interesting thing was that these articles drew contradictory conclusions, some indicating that indeed grapes are toxic and some indicating that they are not! “Which is true?” I began to wonder. 

Having spent several decades professionally reviewing research articles for various jobs, I was immediately suspicious of this research, first because the sample size of only 43 dogs is quite small. A well researched study from which one can with draw conclusions with reliability must have considerably more subjects, ideally of a wide variety of dogs. This study fell short, which indicated to me that it could be a mistake to make generalizations from it. Second, retrospective studies rely on data from other published studies – analyzing the work of others and drawing conclusions “from a distance.” Again, my training and experience in research review cautioned me about drawing conclusions from this kind of research. Further, Lola and I had been sharing grapes for over a year and Lola had shown no negative affects whatsoever. Of course, my experience was not part of a controlled scientific study and thus I was unwilling to draw any firm conclusions from it either. 
I immediately suspected that if grapes had been toxic to the dogs in the JVIM article, the toxicity might have been due to tannin, which is found in the skins of red grapes. Tannin is a known toxic substance and is the culprit causing headaches in some people who drink red wine. (Red wine gets it color from the inclusion of the red grape skin in the fermentation process.) 
An article on regarding grape toxicity indicated that tannin had been found to have not been the causative agent. Unfortunately, no source for this information was cited. web site had posted the results of a survey from 130 dog breeders on the subject of grape poisoning in dogs with zero respondents reporting dog deaths from the injection of grapes. ZERO deaths. However, this was a survey, not a scientifically controlled experiment. 
Two different web sites attempted to take into account the weight of dogs in relationship to the supposed toxicity of grapes. One site reported that 0.7 ounces of grape per kilogram of dog was toxic, with the other reporting 0.18 ounclesl of grape per pound of dog. Converting kilograms to pounds, the first would allow almost twice the amount of grapes than the second. Confusing? Unfortunately, again the specific source for these figures was not reported on either site. 
What I did note was that my dog medical reference — The University of California at avis School of Veterinary Medicine Book of Dogs: A Complete Medical Reference Guide for Dogs and Puppies (1995 edition) — does not include a discussion of grapes in its section on poisons. 
What I eventually realized is that as far as I could determine, there have been no actual controlled scientific experiments to determine the toxicity of grapes for dogs. There are numerous postings of various human foods which are considered to be toxic and yet there appears to be little or no actual research behind any of these lists. I am thus reluctant to include any list of human food supposedly harmful for dogs because the lists appear to be based more on opinion and limited individual experience than on actual scientifically controlled study. But then, I do not believe that dog owners in general would be supportive of deliberately feeding our beloved animals various human foods in order to see whether or not the dogs survived. 
All that I am willing to conclude is that my KBT who weighs 50 pounds does not seem to have been harmed by ingesting three or four grapes a day. At the price of white grapes I am unwilling to share more than that with her! I am interested in hearing about your experience if you feeding your KBT grapes or use grapes as rewards. Keep an eye out on the web site for a survey on this matter 

No portion of this article may be reproduced without permission of the copyright holder. Reprinted with permission from KBFT .

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