Are there any additives I can combine with my cat’s food to lessen the smell?
uh, what’s wrong with cleaning the litterbox?
Is it really the feces that is the main culprit of the catbox smell in your case, or is it the urine?
If you are talking feces, then the real thing to do is to simply change food. Cat foods have an incredibly diverse makeup (even moreso than hotdogs 
) and it is likely that a brand next to yours on the shelf may make their feces smell lemony fresh. Give it a try.
Hill’s Science Diet and others all claim that they are much easier to digest, and are supposed to reduce problems. It all smells the same to me, even at $30 a 20-pound bag.
Change the litter box frequently. You can try sprinkling some baking soda in the bottom of the box (about a quarter of a box per change) and sometimes that helps. But shit is gonna stink.
I know of nothing you can put in the food that would reduce the smell. Many people claim that feeding the cat only high quality cat food will make it better. I have no first hand knowledge of that.
One thing you can do is buy good kitty litter and a litter box with a cover. Scoop the litter frequently and add a little bit of baking soda to the litter.
I never notice a smell from my litter box and my cat eats nothing but Purena Cat Chow.
Hmmmm…datapoint. I’ve got two variables: A brand new cat and I’m using IAMs not Hill’s for the first time ever (my first cat needed Hill’s Perscription Diet and I just kept buying the regular Hill’s from inertia). And this guy’s poop smells far worse than any other cat I’ve ever had. We’re talking biohazard, eyes watering, blistering-paint bad. [sub]Well, maybe not that bad, but Lord it ain’t good![/sub]
Clearly a rigorous experiment must be conducted. Once I’ve finished this bag of IAMs, maybe I’ll try feeding my new cat Hills and see what happens. D’ya think I could get a government grant to conduct this important experiment?
Fenris
Well, my cat gets Iams exclusively and there is no smell at all from the feces. The cat box is in the bedroom and I don’t add anything special to it.
My father’s cat (as well as previous cats I have had) got the store brands (Purina, Meow Mix) and boy was that bad! Also, a cat on Iams (or Hill’s I would assume) will only defecate once every day or so. It seems to me that cats eating the store brands (which have more filler and require larger serving sizes) visit the litter box quite a bit more often.
Also, my cat’s turds are compact “tootsie roll” type. The other cats produced looser stools (sometimes steaming piles; sometimes just squishy) that were not nice at all.
Maybe I just have a considerate cat.
A little rat poison, such as D-Con, mixed with in Fluffy’s 9-Lives does the trick.
That cat crap smell will be gone in no time.
Seriously, though, as soon as we made our indoor cat into an outdoor cat, the smell was gone, as was the cat piss smell, the allergies, and the her fur on everything. Plus, she still kept the mice away. It was the smartest thing we ever did.
Some cat lovers here will be offended by your attempted joke about giving cats rat poison, gwar. Might I also add that there are many good reasons for cats to be kept indoors all the time. We could use fewer predators on natural species of song birds and reptiles.
We feed our cats Iams Adult formula and their poop doesn’t smell much (unless you’re right there when Fluffy takes a poop…I mean, you know she’s pooped, but it really doesn’t smell too bad.)
It’s the PEE that smells.
(thread-stealing question…don’t wanna use that H-word)
My two-year-old fixed male cat has suddenly started marking things. It stinks! Why would he start that and how do I get him to stop?
Ooohhh…I feel for you. You need to stop this immediately, or you are going to face potentially 12 more years of it. I did. 
Look for anything that is a significant change in his environment. Think like he does. Have you blocked a favorite window? Has furniture been moved? New baby, or new pet? Sometimes changing cat food can even cause this.
Getting them to stop is a crapshoot (no pun intended). It is a topic that has been covered here a few times before, and lots of people have had good suggestions. Try searching for it, and I think you will find all that anyone knows about it.
Good luck.
You could always try to become the alpha cat in the household by marking things yourself (like the catbox) 
That would probably confuse the heck out of the cat!
we use this kitty litter that reduces the smell and is reusable…
It is little gel crystals, when the cat poops or urinates on ir it soaks up in the gel stuff.
It lasts longer than regular litter but costs more.
To re-use it you need to remove the chunks and set the tray out in the sun for a while, after a while the yellowness disappears and there is some ready to use litter.
I’ve been using this litter that has those crystals and clumping litter mixed together, and it works great! I also have a covered litter box with a small electric fan on top that runs the air through a charcoal filter. You might think that it sounds a bit elaborate, but with 3 cats it’s a necessity.
We have a cheap contact switch under the box, which turns on a fan. The box is in the garage and the fan vents into the alley. Cheap, low-tech, and effective.
Another idea is if you can catch him in the act, push his tail down while he’s doing it. They really, really hate that. My MIL claims she got her cat (a 24lb…yes 24lbs! fluffball) to stop spraying that way.
FTR, I feed my cat Science Diet and there is no poop odor. Pretty much like rabbit pellets.
KV, are you feeding the cat canned food? I don’t know, but I suspect that “wet” food makes the odor problem much worse. Of course, my cat has never had canned food so she doesn’t know what she’s missing. I can imagine that it’d be hell taking canned food away from a cat that was used to it.
I had a problem for a while with my cats urine smell(and one started peeing outside the box!) I asked about it in this forum and took several of the suggestions. The one that seemed to help the most was getting a second litterbox. The two of them had lived together for a while, so I don’t know WHY it worked, but it did. I cleaned the carpet spot really well, kept their food the same, cleaned the box twice a day instead of once, and got that second box.
Eukanuba is another premium food that will reduce stool amount/odor.
As someone who has, at any one time, 30-50 cats (I breed, plus am a sort of ‘unofficial’ cat shelter), I cannot speak highly enough of the new ‘crystal’ litters. Not only do they stop the urine smell dead in its tracks, they dry up the feces so that the smell is reduced from that, too. Wonderful, wonderful stuff! Hallelujah!
I use a litter called Feline Pine which helps quite a bit. It’s made of compressed sawdust pellets which expand as they absorb the liquid. It also dries up the solids pretty well and lowers the odor quite a lot. I found it to be cheaper than the crystals which is why I use it.