Lions and tigers can't purr

Posted: Saturday, August 29, 2015 

By Bob Bamberg

There's a saying among veterinary professionals that goes something like, "If it roars it can't purr, and if it purrs it can't roar. That refers to the fact that the big cats, like lions and tigers, roar but can't purr, and the small cats such as house cats and mountain lions purr but can't roar.
Although cheetahs purr, and for my money, that's a pretty big honkin' cat. So is the mountain lion. But I digress. The domestic cat begins purring a few days after it's born, which many professionals believe is part of the bonding mechanism between kitten and mom.

Just as barking is to domestic dogs and wild canids; purring is a uniquely feline trait that lasts a lifetime. The difference between purring and other vocalizations such as meowing and hissing is that purring can occur when the cat is either inhaling or exhaling and whether the mouth is open or shut. The other sounds can happen only upon exhalation.

It was once believed that purring occurred as a result of blood flowing through the inferior vena cava, the blood vessel that carries blood from the lower part of the body into the right atrium of the heart.

But contemporary thinking holds that the laryngeal muscles play a key role in purring. From what I've been able to determine, it seems that the absence of purring in cats with laryngeal paralysis was a big clue. It all has to do with the chemistry and mechanics of purring. The chemistry part involves the brain; the mechanics involve the throat and diaphragm. You're probably familiar with the "feel good" hormones called endorphins. Well, they're also "feel-bad" hormones.

Endorphins are released in the brain as a result of things cats find pleasurable, such as being petted or groomed, eating, relaxing, etc. But they're also released during times of stress, such as when in pain or when frightened. That's why cats often purr when injured.

Once the endorphins have been released, the brain sends marching orders to the muscles associated with the larynx, or voice box, and to the diaphragm. The diaphragm forces air across the vocal cords and the laryngeal muscles vibrate the cords, producing the low frequency purr.

An interesting side note is that NASA researchers, investigating bone stress on astronauts in zero gravity, determined that bones heal optimally at sound frequencies between 25 and 50 hertz (vibrations per second). That just happens to be the frequency range of the cat purr.

This has given life to a theory that the cat's purr is a healing mechanism as well, that can rejuvenate muscles, ligaments and bones; keeping them in optimal condition for life as a hard working predator.

Some researchers further believe that purring can help heal bones following an injury, as well as reduce swelling and provide some pain relief. There is still debate within scientific circles about the healing properties attributed to purring, and the jury is still out. Being one who questions everything, and since purring is believed to have healing qualities, I can't help but wonder why other hard working felid predators such as lions and tigers can't purr. No cats work harder, nor bring down larger prey, such as water buffalo and stuff. I'll bet they often end of with sore muscles and joints. Just sayin.'

Bob Bamberg has been selling products for, and writing about, pets, livestock and wildlife since the early '90s. He can be reached at petsap@comcast.net.

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