Why does cat pee stink worse than dog pee? | Dr. Justine Lee, DACVECC, DABT, Board-certified Veterinary Specialist

Posted by justinelee in Animal Safety, Blog, Fun Stuff, Pet Health

For those of you who have ever fostered a tomcat or had an alley cat in your backyard, you can attest to the fact that cat pee reeks way more than dog pee! But why? Cats have much stronger concentrated urine than dogs. The normal concentration of urine is based on specific gravity (often abbreviated “sp. gr.” or “spgr,” for those really lazy vets, such as myself), which measures the density of a liquid (i.e., how concentrated that liquid is). Using a simple tool called a refractometer, your veterinarian can check the concentration of your cat’s urine. Normal cat urine specific gravity is greater than 1.040, while a dog’s specific gravity is normally 1.018 to 1.025. This may sound like a lot of medical mumbo-jumbo, but what it boils down to is that dogs have much more dilute urine, which means that it is less foul, less concentrated, and less yellow in color than cats.

Cats have such concentrated urine because they originated from the desert and have a very long loop of Henle, the part of the kidney that results in filtration and concentration. While you too have a loop of Henle (tres romantique!), yours isn’t as long as your cat’s, so you don’t usually concentrate your urine quite as much (unless you’re hiking in the woods and not hydrating adequately!). A cat’s loop of Henle is so good at squeezing every last drop of absorbable water out that this concentration makes the urine smell quite foul. As a result, cats absorb a large amount of water from their urine to maintain their hydration, which also explains why you hardly ever see them drink – they’re so effective at concentrating! The good news is that it comes with some benefits: not only do cats urinate less than dogs (can you imagine scooping a litter box for a dog?), but it’s also a lot harder for bacteria to grow in their bladder with such a concentrated fluid. Sometimes this can result in problems if your cat has a history of developing bladder crystals. The more concentrated the urine is, the more concentrated the crystals become, which could turn into a bladder stone.

Male cats that have not been fixed have the added effect of testosterone, which makes their urine ten times more stinky. You can minimize the occurrence of this foul urine in your cat’s litter box or the behavioral problems of marking (spraying disgusting urine all over the walls of your house) by neutering your cat before eight to nine months of age.

If you notice your cat’s urine is too dilute, not typically as foul as usual, or if the urine clumps in the litter box are getting too large, contact a veterinarian, as this is often a sign of underlying kidney disease, thyroid problems, or even diabetes mellitus. Your cat isn’t trying to drink more than eight glasses of water a day just to alleviate your sense of smell when you pull litter box duty, so something may be wrong.