good questions.
Grains used in cat and other pet food are paramount to processed junk food, fillers, not good quality food at all - if cats are eating mice, rats and birds, the grains they would get would be partially or fully digested and they would be unprocessed wild and or whole grains not bleached or processed in any way.

Hi Petra...how are all of your felines getting on? In addition to what Mazer said, I might add that your question is one that also pertains to human nutrition. Mice, rats , and birds eat a much more 'natural' diet than factory farmed livestock do. Soy,corn, and wheat are not the natural choice for grazing animals like cows and barnyard birds like chickens. I may be wrong about this, but I believe that is why lamb is so expensive...sheep still graze on grassland and have not been effectively factory farmed.

Just as ruminating animals can digest and break down the proteins & nutrients in cellulose fiber from grass and we get that benefit from eating their meat, the carbs in the digestive track of feline prey are pre-digested so cats (who have shorter carnivore intestinal tracs)don't have to do the work. Also, these carbs add up to a very minor % of the calories prey provide.

mazer, I actually saw a website which sells ground mice. :o]

Lisa, thanks for asking, they are all hanging in there for now, knock wood!!
Yes, that makes sense. We've switched to grass-fed when we do eat red meat, mostly because the cows have a good life, and also since it's supposed to be much healthier than grain-fed.

I do believe that cats need grains and greens because those living outdoors certainly get both. We have indoor/ourdoor cats in that they live outdoors in all but the most frigid weather. Because our last two winters were so brutal, they were indoors most all of the time.

They definitely are not as healthy indoors as when they are out. Even in the spring/summer, they always have access to dry food, but being supplemented with their natural outdoor food tends to be very beneficial to them all.

Cats cannot digest grains or any plant-based protein at all. What they ingest from the GI tracts of their prey is a small amount which pretty much comes out as ingested. Just like the fillers in commercial cat food, which are added because they are cheaper than meat (but end up being way too much % of diet).

Cats also sometimes leave the stomachs of their prey uneaten. As Meg noted, even if the stomach is consumed, its contents are going to make up an insignificant portion of the total prey animal.

I always pondered this same question relative to wild canids, so I called an area federal wildlife specialist to ask about wolves (we have a healthy timberwolf population here). He told me that wolves don't eat stomach contents. They tear the stomach open and eat the stomach lining only. So wolves, at least, don't eat grains or greens as part of their normal diet.

Laurie