One of the most amazing things about canines is the astounding range of sizes and shapes they come in. From Saint Bernards to Chihuahuas - and everything in between – there’s a dizzying array of physical variations. This explosion of varieties has happened extraordinarily quickly in terms of evolutionary timescales due to relentless selective breeding by humans and, as a result of our genetic meddling, the dog is now the physically most diverse land animal on the planet.

With the multitude of shapes and sizes in the canine kingdom, you may be surprised to note that only six or seven locations in a dog’s genetic code can explain about 80% of the differences in height and weight among dog breeds. In comparison, in studies on humans, like those conducted by Carlos Bustamente, professor of genetics at Stanford, differences in height and weight in humans are controlled by hundreds if not thousands of genetic variations.

It’s obvious that pet parents of large and small dogs have some very different experiences with their companions. For one, everything costs more with big dogs, from food to medication. Practically speaking, when a tea cup poodle - weighing in at a mere 5 pounds - doesn’t want to get in the car, the pet parent has the option of just picking him up. However, this seemingly simple solution is not feasible when dealing with a 150 pound Great Dane. Also, people play games like “fetch” more and are more likely to take big dogs out running and biking (Arhant, et al). But there are some significant similarities as well - dogs of all shapes and sizes love human interaction and playtime, need walks, are trainable to different degrees and wag their tails or stumps. They also chew on shoes, can be afraid of thunderstorms, can have fear or dominance aggression, bark, dig in the flowers and jump on people. While we know that people treat big dogs differently than little ones, do these variations in height and weight actually account for real variations in behavior between large and small dogs?

Research published in 2010 reported some interesting findings when comparing the perceptions, behavior, and training of big dogs versus small dogs (Arhant, et al.). Scientists compiled and reviewed 1,276 questionnaires completed by pet parents about their perceptions about the behavior of dogs of different sizes. Researchers found that smaller dogs (under 40 pounds) are seen as less obedient, more aggressive and excitable...and more anxious and fearful. Note that this doesn’t mean that small dogs necessarily are, but are, as a rule, perceived as such.

The researchers also found that pet parents of small dogs not only reported doing significantly less training and play activities, but also a lower level of consistency in their interactions and enforcement of rules than did those with larger canines. An aggressive Chihuahua won’t elicit the same terror as a feisty Doberman, even though another study (Guy, et al.) confirmed that the average “biter” tends to be a smaller dog. Is it possible that a greater tolerance for aggression in so-called ‘mini-mutts’ allows behavioral genetic tendencies to persist?

In general, pet parents often teach larger dogs behaviors that inhibit impulsiveness and lead to emotional control, such as ‘sit’, ‘down’, and ‘stay’. A Maltipoo who lives in a purse usually does not learn these commands: small dogs may indeed be perceived to be more excitable than big dogs because they receive less instruction in emotional control. As one can easily imagine, a 120-pound English Mastiff dances, leaps and charges through the house and 6-pound Affenpinscher doing the same thing are two very different experiences.

Small dogs can also elicit the ‘awww factor’. Anybody who has seen a Pug puppy – well, any puppy, really - knows what I’m talking about. We are evolutionarily hardwired to find baby-like qualities, such as big eyes, tiny statures and proportionally large heads endearing. These babyish features actually engage an emotional response, shifting us into a primal caretaker mode, which is why we find it difficult to resist the puppy in the window. Some scientists propose that dogs with pronounced baby features (Chihuahuas, Boston Terriers, Pugs, Cavalier King Charles Spaniels, Japanese Chins, Shih Tzus, French Bulldogs, etc.) actually affect our hormones - raising the levels of oxytoxin, which is nicknamed the ‘love hormone’ and plays a role in monogamous relationships and the mothering of newborns. With all that oxytocin-inducing adorableness, who can fault pet parents for letting their itty bitty pups misbehave?

I’m interested in your experience. If you’ve had both large and small dogs, do you find that you treat them differently? Expect different behaviors from them? Are there any other ways you think of them differently? I encourage you to share your thoughts in the comment section below.

Thank you so much for all you do to make the world a better place for companion animals.

   Dr. Jane Bicks

References

Arhant, C., Bubna-Littitz, H., Bartels, A., Futschik, A., Troxler, J. Behaviour of smaller and larger dogs: Effects of training methods, inconsistency of owner behavior and level of engagement in activities with dogs. Applied Animal Behaviour Science, Vol. 123, Issue 3, March 2010: 134-142
Guy, NC et al. Risk factors for dog bites to owners in a general veterinary caseload. Appl. Anim. Behav. Sci. 2001 74(1):29-42.

Nagasawa M, Kikusui T, Onaka T, Ohta M. Dog’s gaze at its owner increases owner’s urinary oxytocin during social interaction. Horm Behav. 2009 Mar;55(3):434-41. Epub 2008 Dec 14.

Westgarth C. et al. Dog-human and dog-dog interactions of 260 dog-owning households in a community in Cheshire. Veterinary Record. 2008 162(14)436-442.