By Dr. David Gross
Why do dogs greet each other by sniffing under their tails?
Both male and female dogs and cats have almost vestigial scent glands known as anal sacs. They are located on either side of the anus at 5 and 7 o’clock. Even in modern dogs, the glands secrete an oily substance with a characteristic and individualized — to other dogs — odor.
Because the sense of smell is so acute, your dog can, and does, identify other dogs from this odor. When your dog greets a new dog for the first or even second or third time, this behavior can be quite intense and even annoying to some of us. After the dogs become better acquainted, the behavior reduces in both duration and intensity. The dogs know each other. Cats are much less inclined to do this, probably because they are so secure in their own skin and they don’t really care. However, I have observed this behavior by felines, especially in intact male cats.
Under normal circumstances, the anal sacs partially empty each time the animal defecates. Wild predators, both canine and feline, may mark their territory by rubbing this portion of their anatomy onto trees, rocks, etc. In some dogs and cats, the anal sacs don’t empty and must be expressed manually or they will become impacted and, in some cases, infected. Your veterinarian can do this for your animal and show you how to do it, if you are up to it and ask.
If your dog is “scooting” on his or her rear end, this could be an attempt to express the anal sacs. Sometimes dogs will do this as a way to clean themselves after defecating, so it is not always an anal sac problem. However if the behavior is persistent, you need to have it checked. Other signs of potential anal sac problems include persistent licking or biting of that portion of your animal’s anatomy. Impacted or infected anal sacs need treatment by your veterinarian.
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D. R. Gross graduated from Colorado State University’s veterinary school in 1960 and was in private practice for ten years. He enrolled in graduate school at Ohio State University earning a M.Sc. degree in 1972 and a Ph.D. degree in 1974. He retired in 2006 as Professor and Head of Veterinary Biosciences, at the University of Illinois, Urbana-Champaign. Dr. Gross is a Fellow of the Cardiovascular Section of the American Physiological Society. During his academic career, he published over 90 papers in refereed scientific journals and over 100 abstracts in proceedings of scientific meetings.