Tag Archives: Virginia Tech

Dogs may be sloppy drinkers…but they get the job done

Researchers at the Virginia Tech College of Engineering can tell the story of dog lapping.

Using photography and laboratory simulations, researchers studied how dogs raise fluids into their mouths to drink. They discovered that sloppy-looking actions at the dog bowl are in fact high-speed, precisely timed movements that optimize a dogs’ ability to acquire fluids.

Old dog drinking

They have published their research in the Proceedings of the National Academy of Sciences.

Researchers also compared what they learned about how dogs drink with what they knew from previous studies of cats. The scientists discovered that even though feline and canine mouths structurally are similar, their approaches to drinking are as different as — cats and dogs.

“We know cats and dogs are quite different in terms of behavior and character,” said Sunghwan “Sunny” Jung, an associate professor of biomedical engineering and mechanics. “But before we did fundamental studies of how these animals drink fluids, our guess was dogs and cats drink about the same way. Instead we found out that dogs drink quite differently than cats.”

Dogs and cats are biting animals and neither have full cheeks. But without cheeks, they can’t create suction to drink — as people, horses, and elephants do. Instead they use their tongues to quickly raise water upward through a process involving inertia.

Both animals move their tongues too quickly to completely observe by the naked eye. But dogs accelerate their tongues at a much faster rate than cats, plunging them into the water and curling them downward toward their lower jaws, not their noses.

They quickly retract their tongues and a column of water forms and rises into their mouths, but they also curl the underside of their tongues to bring a tiny ladle of water upward.

Dogs precisely bite down to capture the water. In an instant they reopen their mouths and immerse their tongues back into the water.

Cats, on the other hand, lightly touch the surface of the water with their tongues, usually never fully immersing them, according to previous imaging by Jung and other researchers. When their tongues rise into their mouths, liquid adheres to the upper side, forming an elegant water column.

When dogs accelerate their tongues upwards, the latest research reveals a water column rising, but some water remains in the ladle of the tongue and is tossed to either side of the dog’s mouth or it falls downwards.

Although dogs do not use their tongues to actively scoop water into their mouths, it is possible that the scooped liquid has some positive effect on the water column dynamics below the tongue, the researchers said.

“Dog drinking is more acceleration driven using unsteady inertia to draw water upward in a column, whereas cats employ steady inertia,” Jung said.

In all, 19 dogs of various sizes and breeds were volunteered for filming by their owners. Thirteen of the dogs were filmed outdoors at their owners’ residences in the Blacksburg, Virginia, area. The remaining six were filmed at the Virginia Tech campus.

“This was a basic science study to answer a question very little was known about — what are the fundamental mechanics of how dogs drink?” said Sean Gart, a graduate student in biomedical engineering and mechanics who filmed the dogs. “Cats tend be viewed as neater, dogs are messier, but dogs really have to accelerate their tongues to exploit the fluid dynamics of the water column.”

The researchers measured tongue motion, recorded water volumes, and generally measured lapping in the dogs. They used the results to generate a physical model in the laboratory of the tongue’s interaction with the air-fluid interface, according to Jake Socha, an associate professor of biomedical engineering and mechanics at Virginia Tech.

Source:  Newswise media statement

A close up look at how our dogs drink…

The field of fluid dynamics explains how our dogs drink and why they splash and slop more than cats…

The drinking mechanism of a dog is videotaped from three different angles (A, B, and C). The curved tongue is rapidly withdrawn and a water column is formed underneath. A physical experiment is designed to understand and characterize the underlying fluid mechanics.  Photo by:  Sean Gart and Sunghwan (Sunny) Jung/Virginia Tech

The drinking mechanism of a dog is videotaped from three different angles (A, B, and C). The curved tongue is rapidly withdrawn and a water column is formed underneath. A physical experiment is designed to understand and characterize the underlying fluid mechanics. Photo by: Sean Gart and Sunghwan (Sunny) Jung/Virginia Tech

By studying the drinking habits of various dog breeds and sizes, a group of researchers at Virginia Tech and Purdue University has recently identified and modeled the fluid dynamics at play when dogs drink water.

“Three years ago, we studied how cats drink,” said Sunny Jung, an assistant professor at Virginia Tech. Jung’s research focuses include biofluid mechanics and the nonlinear interactions between soft bodies and surrounding fluids. His current project is sponsored by the National Science Foundation’s Physics of Living Systems program. “I was curious about how dogs drink, because cats and dogs are everywhere.”

As members of the order Carnivora, cats and dogs have incomplete cheeks, which allow them to open their mouths wide to deliver killing blows. But what makes pack hunting possible also makes suction drinking impossible. Unable to seal their cheeks completely, there is no way for a dog to suck up water. Conversely, humans have “complete” cheeks, and we drink by creating negative pressure, allowing us to suck water into our mouths and down our throats.

Cats, too, lack suction, and they compensate by drinking via a two-part “water entry-and-exit” process. This consists of a plunging and a pulling phase, in which a cat gently places its tongue on the water’s surface and then rapidly withdraws it, creating a column of water underneath the cat’s retracting tongue.

“When we started this project, we thought that dogs drink similarly to cats,” Jung said. “But it turns out that it’s different, because dogs smash their tongues on the water surface — they make lots of splashing — but a cat never does that.”

When dogs withdraw their tongue from water, they create a significant amount of acceleration — roughly five times that of gravity — that creates the water columns, which feed up into their mouths. To model this, Jung placed cameras under the surface of a water trough to map the total surface area of the dogs’ tongues that splashed down when drinking.

The researchers found that heavier dogs drink water with the larger wetted area of the tongue. This indicates that an allometric relationship exists between water contact area of the dog’s tongue and body weight – thus the volume of water a dog’s tongue can move increases exponentially relative to their body size.

In order to better understand how the physiology works, Jung and his colleagues could only go so far by watching dogs drink. They had to have the ability to alter the parameters and see how they affected this ability, and since they could not actually alter a dog in any way, they turned to models of the dog’s tongue and mouth. “We needed to make some kind of physical system,” Jung said.

For their model, Jung and his colleagues used glass tubes to simulate a dog’s tongue. This allowed them to mimic the acceleration and column formation during the exit process. They then measured the volume of water withdrawn. They found that the column of water pinches off and detaches from the water bath primarily due to gravity. Dogs are smart enough to close their mouth just before the water column collapses back to the bath.

Source:  Newswise media release