Long time back, I used to have a pet bird and grit was recommended by the vet for the bird.
It seems a lot of animals have gizzard stones (Gizzard - Wikipedia)
“ A bird swallows small bits of gravel that act as ‘teeth’ in the gizzard, breaking down hard food such as seeds and thus helping digestion.”
How does this work, exactly ? If I have some rocks in a pipe, and force grain through it, I will just push the rocks out. Is the gravel attached to something like a sandpaper ?
From cleaning game birds and checking their innards for various reasons, I’ve learned that the gizzard is a strong, rubbery muscle pouch with grit in it, very unlike a pipe. I can easily see how food + bits of stone + said muscle pouch results in breaking down the meal. A crude analogy would be using one’s hand to mash up food.
Basic bird digestion involves a crop, where food is stored and minimal digestion takes place, followed by the proventriculous which is glandular and is where some chemical breakdown of ingesta takes place. After the proventriculous comes the ventriculous (duh), or gizzard, a muscular organ where ingesta is digested further.
Ingested stones help to physically break down ingesta.
Thank you Toxylon. Sort of like taking a baked potato in your hand and crushing it while forming a fist ? If that’s the case, how does the presence of small rocks in your fist effect the crushing process ? In my experience, it doesn’t.
Kayaker, agreed. I am trying to understand the mechanism by which this happens. An analogy will be very helpful.
In the same way that the presence of small mineral deposits (teeth) in your mouth helps in shredding food. The pebbles aren’t fixed in place, of course, but I think while the gizzard is contracting they shouldn’t move around too much.
Since the gizzard is a rubbery pouch, let’s go with a big balloon. Say you put some corn kernels in there are give it a few squeezes trying to grind them to pulp. You’d squish some, but the outsides are too tough for you to really break them down. So you add in some pebbles and try squeezing again. The pebbles are rough enough to tear up the outer layer of the corn, and as the kernels rub between them they get ground up between them like grain in a stone mill. You’d eventually be able to grind up all the corn using the pebbles.
As the gizzard muscles contract, they grind the bird seed, or whatever the bird eats, against the grit stones to break up the outside seed coats into something the bird can digest.
Thank you tricoteuse, that makes sense. Except that the pebbles will get mixed with the corn flour and will leave with the ground mix. No ?
The smaller pebbles probably pass through with the food and get pooped out eventually. I’m not really sure. But inside the gizzard it would be wet from the bird drinking water at least (do birds salivate? or the gizzard secrete some kind of digestive juice?). Like if you added water to the stuff inside the balloon, then made a small hole at the bottom. The corn goop would run out but the pebbles bigger than the hole would stay behind.
Too late to edit my last post,.
OK, I read the Wikipedia article about gizzards and I think I get it. The first part of the stomach is where the digestive juices are added to the food. Then it passes into the second part of the stomach, the gizzard, where the whole works gets mashed around with the pebbles. So the stuff that then goes into the intestines would be pretty well liquified.
The fact that birds need to eat grit as an ongoing part of their diet says that the grit is also passed. As a fledgling presumably they need to eat an initial “loading dose” to populate the gizzard with grinding media, but after that they just need to eat as much as is necessary.
Having dissected a couple of gizzards, it’s like a single-chambered heart. Very muscular with only a small percentage of the volume being the internal cavity. Not like a thin-walled balloon that’s mostly empty space. Think more like a mortar and pestle with some seeds & some sand in it.
The processing cycle is somewhere between purely batch and purely continuous flow. In that sense a bit like human chewing and swallowing but slower. We put food in the mouth, tear it up for a few seconds then push it along, lather rinse repeat. It’s pulsed continuous flow.
Pet birds fed a pelleted diet do not need grit. I’ve raised budgerigars, cockatiels, a yellow-naped Amazon parrot, and a Congo African grey parrot. None of my birds ever had grit.
In fact, pet birds offered grit can over consume it and become ill.