If you have not experienced this reaction from your own dog, you have certainly seen it on YouTube or in the park. An owner who did not scratch their dog’s belly to see them kick is an odd prospect, I will give you that. Why do dogs kick when you scratch them, though?
The answer is pretty simple, just like the role of it. However, the importance it has is bigger than you might have thought. It goes back to their ancestors and is one of the things that kept dogs alive for tens of thousands of years. Here is the breakdown.
Scratching Reflexes Are Part Of Dog Evolution
How did dogs survive before humans domesticated them? Without all the advancements in veterinary medicine and biochemistry, our dogs are still plagued by the simplest of health problems.
While there is nothing wrong with an injury or infection, parasites have been around since all beings on Earth were ingredients of primordial soup. Evolution brought parasites, and the subsequently evolved creatures, including canines, had to suffer the consequences.
For canine ancestors, the first wolves, the scratch reflex was the primary line of defense against parasites that we know today as fleas and ticks. As the transmitters of various debilitating and fatal diseases, their presence on a canine’s skin was most unwelcome.
Scratching them off was the main way to get off as many as possible, so the most immobile area of their body, the abdomen, and flanks, specifically relied on using the hind legs and paws to remove the pests.
This area was named the saddle due to its saddle-like appearance and is the only region of a dog’s body where the scratch reflex can be triggered by external stimuli, i.e., our hands. The belly of a dog is known as the “receptive field of the reflex.”
Other parts of the body are more easily accessible, so scratching is not the only way to prevent parasite infestation, which means that the nerve endings network of the saddle area is highly sensitive.
The Locomotion And Delay
It takes a while for the legs to catch up to the scratching, so your dog’s nerve endings will slowly but surely transmit the message into the brain. At first, the leg movement will be short and sluggish, but it will gain momentum as impulses travel to the neurons.
It is interesting that C.S. Sherrington’s book on this nerve network and scratch-reflex says all dogs had the same rate and speed of leg movement despite the type of stimulus given.
That means that an itch, hand scratch, or electric stimulus, all resulted in the same movement for every tested dog. The reach of the foot and area covered by it was almost identical between different dog breeds.
Seeing the leg move rhythmically and gradually get faster is reminiscent of a locomotive. The transfer of electric signals from the peripheral nervous system (PNS) creates the delay, and the intensity of the stimulus increases the kicking speed.
Another interesting find found in Sherrington’s study is that not all areas of the saddle seemed to trigger the scratch-reflex. Regions closer to the post–thoracic spine innervation were more easily excitable than the thoracic ones.
It was a common belief that the scratching of the belly in dogs was a voluntary action, but it was later discovered that it was indeed a reflex. Why is it not voluntary? Because evolution made sure that dogs survive by putting urgency in getting rid of the parasites.
Leaving them on for a day by not scratching away at the belly would have made dogs extinct by now. This shows how a simple thing, with a rudimentary role, can be extremely complex to develop.
Health Conditions That Can Increase Sensitivity
Naturally, the nervous system is located through the layers of the skin, so any condition that affects it can increase sensitivity. In dogs with allergies, the response can be elicited quicker than in dogs with healthy skin.
Whether environmental or food allergies, the symptoms will most likely include itchy skin, redness, and potentially bumps. Itching from allergies will affect the head, ears, anus, and other parts of the body as well, so keep an eye out.
Testing your dog for allergies is a smart move if you notice an affinity or sensitivity to belly rubbing that activates the scratching. However, there are many more skin-related diseases that overstimulate the saddle area.
One such condition is pyoderma. It is a bacterial infection that most often happens due to excessive damage to the skin caused by scratching. The bacteria that enter under the uppermost layer of skin can then cause symptoms other than itchiness, like scaly skin or pustules.
Inflammation of hair follicles, or folliculitis, is something that can happen when brushing your dog too aggressively. A brush will pull the hairs out and cause damage to the follicles and adjacent skin, leading to itchiness, sores, scabs, etc.
Luckily, the treatment for these conditions is effective and widely available. Pyoderma can be treated with antibiotic ointments, while folliculitis is easily treated and managed with antimicrobial shampoos, ointments, etc.
Last but not least, mange is a serious condition caused by mites. As with many other parasites like fleas and ticks, the skin becomes reddish, itchy, and often involves patches where hair has fallen out. Treatment consists of special shampoos and oral medication.
The Scratch-Reflex Is A Useful Tool For Diagnosis
Yes, a scratch reflex is completely natural and deeply embedded in the genetic code of canines. Dogs that are suffering from conditions that do not exhibit symptoms until reaching advanced stages, like degenerative myelopathy, can benefit from this reflex.
If you notice your dog’s scratch-reflex cannot be triggered, there might be some health issue involving the nervous system. Degenerative myelopathy is a debilitating disease that progresses quickly but shows symptoms only mid-stage.
With a scratch-reflex trigger that is ineffective or shows odd leg movement, it is reason enough to visit the veterinarian as soon as possible. An early DM diagnosis can delay the progression of the disease through physical therapy and specialized diets.
German shepherds are among the breeds most prone to developing degenerative myelopathy, so if you suspect your dog might have it, read about the five must-know symptoms of the condition.
Similarly, a tumor pressing on the nervous system can be diagnosed sooner thanks to the scratch-reflex, which will be either inhibited or triggered by seemingly nothing.
Scratching To The Conclusion
This answer to “Why do dogs kick when you scratch them?” should be exhaustive enough to satisfy your curiosity about this uniquely canine phenomenon. Next time you scratch your dog’s belly, think of it as a button that starts a train engine.
Do not overstimulate the saddle region, or you might have a “I scratch your back, you scratch mine” relationship with your dog. Only the back is the belly for the dog. Cheers!