Tryptophan Supplements for Dogs

Everyday it seems like I learn something new from pet owners. I was looking at some of the search terms people have been using to find my website and I discovered that quite a few people found my post about dog vitamins by searching for the term tryptophan supplements for dogs. Since I had never heard about giving tryptophan to dogs I decided to research the topic to learn more about it.

When I research any health topic about pets there’s usually four places I visit because I find them to be the most credible:

The first is PubMed which is a database that contains millions of abstracts from every medical and scientific journal you can imagine. You’re usually only given permission to read the abstract (unless you want to pay extra) but usually the abstract contains all the information you really need to know. The abstract is more or less a summary of what was discussed in the article.

The second is Medline Plus which is a service of the U.S. National Library of Medicine and the National Institutes of Health. Usually the information is directed more toward human medicine but much of the information can be applied to pets and animals as well.

The third is the Journal of the American Veterinary Medical Association. Since I’m a licensed veterinary technician I have access to all of the AVMA journals online from 2000 to the present. However, all of the abstracts are available to you on PubMed.

The fourth is my own personal library of veterinary textbooks which I’ve collected over the years as well as the textbooks we have at the clinic. I know you probably don’t have access to your own personal library of veterinary textbooks but if you’re lucky enough to live near a veterinary school the library there should have every book on animal medicine you can imagine. You probably won’t be able to check out the books but you can still oogle over them.

OK, so based on my research here’s what I learned about tryptophan and dogs:

First, it’s important to know that tryptophan is an amino acid and a very large one at that. In fact, tryptophan is the largest of all amino acids. This may not be so important if it wasn’t for the fact that tryptophan has to compete with other large amino acids for a ride across the blood brain barrier. Tryptophan is also a precursor for serotonin, so decreased amounts of tryptophan will lead to reduced formation of serotonin. This may possibly lead to more aggressive behavior in dogs. In humans, serotonin is thought to produce a “stable mood.” Tryptophan is an essential amino acid which means the body is unable to produce it so it must come from the diet.

The link between the dietary protein content found in food, metabolism of the amino acid tryptophan, and aggressive behavior in dogs has been the subject of great interest for a relatively small group of veterinarians and scientists who study animal nutrition and behavior. According to a study I found in JAVMA, for dogs with dominance aggression, the addition of tryptophan to high-protein diets or a change to a low-protein may reduce aggression. For dogs with territorial aggression, tryptophan supplementation of a low-protein diet may be helpful in reducing aggression.

It seems like with anything else, the only way to know if your dog will respond to a tryptophan supplement is to try it out for yourself. Also, if you haven’t already, I would recommend feeding your dog a low-protein diet first before supplementing with tryptophan. In another study on the effects of dietary protein on the behavior in dogs, the lowest protein levels fed to dogs was 17%.

Unfortunately, it’s impossible to accurately determine the protein level of dog food by reading the label. You may notice something listed on dog food labels called the Guaranteed Analysis. This lists the crude protein as a minimum number based on percentages. The percentage listed on the label indicates the “worst case” levels for protein in the food and does not reflect the exact amount.

For example, a dog food that has a label claim of “minimum protein 30%” cannot have less than 30% protein, but may have more. It may have 31% or 45% or 99%. We have no idea. For all we know this brand of dog food may have the same protein content as another with the claim: “minimum protein 50%”.

The crude protein level refers to a specific formula that estimates the protein content of the food by measuring nitrogen. The percentage is an index of protein quantity but does not indicate protein quality or digestibility. I clearly don’t understand why pet food manufacturers continue to print the Guaranteed Analysis on the label because all it does is confuse pet owners and gives them totally useless information. Something more useful would be the nutrition information label that is required for people food.

A more accurate way to measure the protein content of dog food is based on nutrient density, caloric distribution and “as fed” values. This topic is a little too in-depth for a blog post on tryptophan, but with a simple phone call the manufacturer of any reputable pet food company should be happy to provide you with this information. Luckily, some companies are smart and understand that a well-informed customer is the best type of customer and are starting to provide this type of information on their websites.

In terms of supplementing your dog with tryptophan, scientists studying the effects of tryptophan added 10mg/kg/meal to the low-protein diets (18%) and 12.5mg/kg/meal to the high-protein diets (30%). The dogs were also fed twice daily or approximately every 12 hours.

If you’re interested in giving your dog a tryptophan supplement I would recommend consulting with your veterinarian first. Chances are, unless they have a special interest in nutrition or behavior, they will probably wonder why you would want to do a such thing. If so, I would point them in the direction of the studies I used as references. Better yet, you might ask them for a referral to a veterinarian who specializes in behavior problems. Even though there may not be a board-certified veterinary behaviorist in your area, there are plenty of veterinarians who like to help owners with behavior problems.

Tryptophan is generally safe but may interact with other medications your dog is taking. Common side effects of supplementation include vomiting and diarrhea. Again, you should never give any medication or supplement without first consulting with your veterinarian. A blood panel and urinalysis is also recommended before starting any treatment program.

References:

Effect of Dietary Protein Content on Behavior in Dogs
Impact of Nutrition on Canine Behavior
Effect of Dietary Protein Content and Tryptophan Supplementation on Aggressive and Hyperactive Dogs
Tryptophan Article by Dr. Dodman
Medline Plus Medical Encyclopedia