Chocolate and Rats

Lori Chaddock
From the Jan/Feb 1996 Rat & Mouse Gazette

Working as a veterinary technician in a practice that has numerous rat and mouse owners as clients I am often asked if chocolate is toxic to their pets. My initial reaction was to apply the same guidelines we use for dogs to murines (rats and mice), but then became curious if there were any actual studies doneon these species which would give specifics. First, it is important to understand what is toxic about chocolate in species that are susceptible to chocolate poisoning. It is the theobromine in chocolate which in large amounts has diuretic effects, relaxes smooth muscles, and stimulates the heart and central nervous system. Caffeine has a greater effect on the central nervous system and is also found in small amounts in chocolate. Pharmacologically, theobromine is included in a group of naturally occurring methylxanthine alkaloids along with caffeine, theophylline, and the synthetics, aminophylline and etamiphylline. Relative to other methylxanthines, theobromine is pharmacologically weak. Theobromine, as well as other drugs mentioned do have therapeutic effects when given at the proper dosage and are used in the treatment of respiratory diseases and heart disease. I have treated my own rat with aminophylline (dose prescribed by my veterinarian) when in the final stages of Mycoplasmosis. This is a bronchial dilator and did offer her some relief. I had a necropsy done atWashington State University and they found no side effects from the aminophylline treatment. Theobromine is found in higher concentration in unsweetened baker's chocolate (15mg/g) than in milk chocolate (1.5 mg/g). White chocolate is low enough in both theobromine and caffeine and would be unlikely to cause poisoning.

I began my search for published information pertaining to rats and chocolate toxicity with my professor Ken Tudor D.V.M. at the college where I am enrolled in the Veterinary Technician program. He contacted his associate Jean Hoffman A.H.T. who specializes and teaches classes on laboratory animals. Neither were able to find any reference material for me on the subject, but suggested I call Dr. Kean at the Laboratory Animal Facility at Loma Linda University. I contacted Dr. Kean, but he also knew of no particular studies conducted on chocolate toxicity in rats. I then began searching my college library and a database at Cal. Poly. Pomona, but I could find no research articles specifically dealing with chocolate and rats, only chocolate toxicity in dogs, so I called a friend who is a veterinarian in Washington, Dr. Wada, with connections to the Veterinary program at Washington State University. She nor her associates at W.S.U. knew of any published information either. I also had the veterinarian I work for and another local veterinarian, Dr. Castiglione, help with the research and both were unable to find any information pertaining to rats, again only dogs. I even put my question on the bulletinboard for veterinarians on America On-Line and received a response from Dr. Brown, who also could not give any specific level, but did say that chocolate can be toxic in large amounts.

I now resorted to opinions from all the above mentioned sources and none wouldstate that a small quantity of milk chocolate would be toxic to a rat. All agreed that they could see no harm in feeding a small quantity of chocolate as a treat along with a balanced and nutritionally complete diet. They did feel that chocolate had no nutritional value and that a less sugary treat would be more beneficial to the rats' diet. Dr. Brown wrote "you would be better off not giving it at all rather than worrying about exactly how much is toxic." Dr. Castiglione specifically suggested not feeding any baker's chocolate, or products such as homemade chocolate cake or frosting made with large quantities of baker's chocolate. I would assume that rats would not even want pure baker's chocolate as it is not sweet and even has an unpleasant flavor. Dr. Kean said that he could see no problem in giving a couple of semi-sweet chocolate chips, even on a daily basis, as long as the rat was receiving a nutritionally complete diet and the treat did not replace this diet. Most were fearful that if they were to tell a client that it is okay to give chocolate as an occasional treat the client would overfeed the treats when they see how much their pets enjoy it. Their shared opinion was that unlike dogs, rats usually do not eat as voraciously and would be much less likely to ingest a toxic quantity of chocolate, even if offered, if they had other nutritional food. The best guideline any could give me is the levels which may cause symptoms to be exhibited by a dog which is about .04 oz (1.3 mg) baker's chocolate or 0.4 oz(13mg) milk chocolate per kilogram (2.2 pounds) of body weight, and doses 10 times higher may be lethal. In simpler terms, this equates to a 5 pound dog needing to consume about a half square of baker's chocolate, or 5 oz. (4 avg. candy bars) to be dangerous.

I was disappointed to find no published facts on this subject and to realize that this concept that chocolate is toxic to rats is based on the fact that in large quantities it is toxic to dogs and feel that most veterinarians are more knowledgeable about canine care and therefore, often apply the same principles to rats. I feel they are also playing it safe by telling clients not to feed chocolate due to the fear that if they give it the okay, a client will give their rat too much and offset the nutritional balance of the diet. I have been active in training and showing dogs for 24 years and was always told to "never feed my dog chocolate." It was not until I began working in the veterinary field and became educated on the actual levels of chocolate ingestion which are toxic that I realized that even if my 27 pound Sheltie stole a couple of piecesof See's candy off the table he wasn't going to die.

My conclusion is that an occasional, small piece of chocolate is certainly not going to kill my rats and I know they really enjoy it. Chocolate has no nutritional value for me either, but I hope no one denies me my Almond Joy! I think the important aspect is for the owner to use common sense when giving this treat, just as in feeding your rats in general. They must be given a complete, nutritious diet. I feel you have a higher likelihood of losing your pet to Mycoplasmosis, or to tumors than to chocolate toxicity.