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Throughout my entire veterinary career, I have maintained that my patients had right or left handed preferences. Subtle observations of preferences or behaviors during my exams suggested to me that, like us, each side of their brain dominated different activities. This week’s issue of the The Economist describes studies by Italian scientists that demonstrate the direction of tail wagging is determined by whether a situation was pleasant or unpleasant.

To Dogs, Left Is Sinister

Two years ago Giorgio Vallortigara and his group at the University of Trento in Italy demonstrated that dogs wagged their tails to the right when greeted by their masters. The same dogs wagged their tails to the left when encountering an unknown dominant dog. Left unanswered by this early study was whether the right or left signal was meaningful to other dogs.

In the new study, Vallortigara and colleagues used electrodes to monitor the heart rates of dogs subjected to videos or silhouettes of other dogs, head on, with tails wagging to the left or right. An increased heart rate indicated an anxiety response. They also noted other stress behaviors like ear-flattening, head-lowering, and whining in response to the videos and silhouettes.

Left tail wagging was consistently associated with prolonged, higher heart rates and stress behavior in the wired dogs. Their heart rate response to right tail wagging or stationary tails was much less. Stress behaviors were also less common when subjects viewed right tail wagging.

These studies suggest that dogs and humans have brain halves that are specialized for specific functions. Handedness and language are human traits that have been established as specific to brain hemispheres. Interesting is that both humans and dogs view the use of left side as “sinister.” In fact, the right side of the dog brain, not the left, initiates left tail wagging.

How This May Be Useful to Dog Owners

Personal safety:

Attention to the direction of tail wagging from an approaching, unknown dog may give an indication of potential problems or a pleasant encounter. The direction of your dog’s tail wagging in the company of strangers may help avoid an unfortunate encounter or presage a pleasant one.

Animal Safety:

As with human encounters, the direction of your dog’s tail wag may alert you to a response to other dogs. This could be very useful in dog parks and other areas where many large numbers of dogs meet for the first time. Avoiding a potential dog fight or expecting a playful, friendly experience is certainly emotionally superior for all concerned.


My Observations of Left and Right Handedness in Dogs and Cats

These studies did not look at whether dogs had right or left hand preferences. So why do I suspect that is the case?

Friendly pawing:

I have noticed over the years that my cat and dog patients had a preference for which paw they presented when greeting me. Often times, questioning of the owners would uncover hand preferences when greeting them or exploratory behaviors around the house

Medical Findings:

Large breed dogs develop very heavy pressure point pads on their elbows. With the weakness of age, these pads are subject to increased friction injury when animals rise. I have observed that these injuries are consistently associated with either the ride or left side, depending on my patient. To me this indicates a preferential side to supporting weight while rising.

I have also noticed many cats that consistently present for fight wounds on the same side of the face or body. To me this suggests a “weak” side. Absent visual problems, it would seem that these cats are stronger at protecting one side over the other. They are like a boxer with a great right jab but a weak left hook.

Is your pet right or left handed?

Dr. Ken Tudor

Image: Susan Schmitz / Shutterstock

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