Every good cat deserves a good poop

Constipation and difficulty defecating are common in older cats. Why is this? A lot of it has to do with the kidneys.poop200

Kidneys filter blood to remove toxins and waste. The fluid and waste products that are filtered go into tiny tubules in the kidneys where, in a very tightly regulated way, some water is pulled out of the fluid and sent back to the blood stream and the rest is sent out in the urine. The amount of water kept or sent out in the urine depends on the cat’s hydration status.

If a cat is dehydrated the body is going to want to keep as much water as it can. The kidneys will pull most of the fluid out of the filtrate and send very little out in the urine, resulting in very concentrated pee. If the cat has a huge meal that is high in water content and then has a big drink (or if you, a human, have a couple of beers) there is a lot of water in the body and more will be sent out in the urine, making the urine much more dilute and watery. The mechanism involved a bunch of hormones and is pretty complex and very precise.

That’s how it is supposed to work, anyway. But most cats over 13 or 14 years of age have some degree of kidney failure. In this disease the kidneys don’t fail to filter the blood initially, they fail to pull back some of the water and they fail to make a concentrated urine. No matter how little water the cat takes in or how dehydrated it is, the urine is full of water that should have been kept in the body. The cat is basically peeing itself into dehydration. They simply can’t drink enough to keep ahead.

(tl;dr – The kidneys regulate water. Kidney failure, very common in old cats, causes dehydration.)

So we have all these older cats with varying degrees of kidney disease and most have some dehydration. We know that dehydration causes the mucous membranes to dry out (think of how the inside of your mouth feels when you are really thirsty). The intestines are completely lined with mucous membrane. As the name implies, mucous membranes make some mucus, but they need to be well bathed in water, too, in order to work properly. Dried mucus is very gluey.

If we dehydrate the intestines, things get really sticky. In the colon the poop doesn’t pass easily, and it takes longer for it to go from the start of the colon to the anus, a trip of about 18 inches. The colon’s job is to suck water out of poop so that we don’t all have diarrhea all the time. This is a time-dependent function, and the longer these cat poops stay in the colon the drier and drier they get. Eventually dehydrated older cats end up pooping little dry nuggets that are very hard to pass. There can be bleeding. A lot of older cats end up not being able to pass a bowel movement for several days, and sometimes this results in an actual obstruction with poop (called obstipation, a combination of “obstruction” and “constipation”).

(tl;dr – Dehydration = sticky intestines = slow transit through the colon = more water sucked out of the poop = hard nuggety poops = unhappy cat with painful bowel movements)

The last thing an older cat needs is to be dealing with hard stools that are painful to pass. I mean, really, everyone deserves a good, healthy poop, especially our beloved old kitties. But what can we do?

A couple of things. First, talk to your vet about the degree of kidney disease your cat has, and whether giving fluids under the skin (subcutaneous or SQ fluids) is appropriate. This will improve the cat’s hydration and make him more comfortable in many cases. Also, changing the cat onto a totally canned food diet (if that hasn’t already happened) will provide a lot more water over the course of the day and help with hydration.

Second, even if your cat doesn’t need fluids yet, if she’s having a hard time passing stools and is forming hard dry nuggets, she needs help. There is a great laxative called PEG that comes as a dry, tasteless powder. It’s not a bulk-forming laxative like psyllium (Metamucil) or bran, and it doesn’t cause intestinal cramps or spasms like some other laxatives. All it does is hold onto water, so that when the sloppy wet digested food (proto-poop, we could call it) travels from the end of the small intestine through the colon it doesn’t get completely desiccated. It makes the stools better hydrated and softer, and much easier to pass.

DEHYDRATED OLD CAT POOP (old cat, not old poop): Hard, dry, nuggets that may or may not even be in the litter box. Usually difficult and sometimes painful to pass. May have some fresh blood on them.

NICE, NORMAL OLD CAT POOP: Should be formed, tubular, and in sections at least 4″ long. It should look, if I may use the forbidden word, moist. You are not looking for pudding; just nice tubes, maybe a little coiled. If it all comes out in one piece, that’s fine too.

(If you want pictures, do¬† Google search on “Purina fecal scoring” and look in Images. You are aiming for a score of 3 to 4; 5 may be a little far and would usually be considered diarrhea. The consistency of the poop emoji is a step too far.)

PEG DOSING: There is a wide range of dosing that will be individual for each cat. I usually start them at 1/4 tsp of PEG powder in each of two meals a day, mixed with the canned food. It is very rare for even a picky cat to object to the powder in the food; I really don’t think they can taste it, and it doesn’t change the consistency of the food. You can also add some water to the cat food, as long as it doesn’t change the consistency so much that the cat doesn’t want to eat it any more.

If you give 1/4 tsp per meal for a couple of days and the poops are still nuggety and dry, increase to 1/2 tsp for a few days. Some cats will need to go up to 1 tsp per meal (twice a day) before things get sorted out. The nice thing is that if you go too far and the poop starts to come out like pudding, you just back off on the dose until you get nice tubular poop consistently.


The brand names for PEG powder include Restoralax, Lax-a-Day, and Miralax. The generic PEG powders are exactly the same and a little cheaper, and available in bigger containers. You should be able to find this poop magic in pretty much any human pharmacy.


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