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Chicken Digestion
Goose Digestion
Further Reading
Cow Digestion
As people learn about the benefits of grass-fed beef they often wonder if the same principle can be applied to other farm animals, which then leads to the question: Do your chickens eat grain or are they also grass-fed?
To fully answer that question (and if you don't want full and detailed explanations, you should probably stop reading my blog posts!) we have to first understand a bit about animal digestion.
The cow is a ruminant. This means that it has a system of stomachs (four in this case) which takes a food that is quite low in calories and nutritional density (grass) and puts it through a fermentation processes, plus an additional round of chewing, to extract as much nutrition as possible. This is made possible by some very hard working gut microbes which do the actual digesting: releasing proteins and nutrients and creating fatty acids. (They also release methane as a by product but that is a topic for another post).
There are herbivore animals that are NOT ruminants. A good example is horses, who can typically live on just grass and have a single stomach, that is they are "monogastric". However, unlike monogastric omnivores (humans, pigs) or monogastric carnivores (dogs, cats), horse stomachs are full of many of the the same cellulose digesting bacteria that populate ruminant stomachs. But while they can digest the tough cellulose in grass, they are less efficient at it than ruminants. This is part of the reason why horse people often supplement their animals' diets with grain and are much choosier about the hay they feed than cow people!
Monogastric animals without this special population of bacteria don't do as well eating grass. You may not eat grass regularly but have you ever seen what happens when a dog or cat chows down? Let's just say that I don't think very many nutrients have been extracted.
Chicken Digestion
Now, chickens. Chickens are not ruminants. They also are not quite monogastric but are still considered "simple stomached". This is because they have an extra organ to make up for their lack of teeth! When a chicken first eats food, it stuffs it into its "crop" which is basically just a pouch to put food in for later, no real digestion happens there. From there the food goes to the proventriculus or "true stomach" where it's mixed with digestive enzymes, very similar to our human stomachs. From there it goes to the gizzard which is where the food is finally "chewed". The gizzard is a big pouch of muscle where a chicken also keeps stone grit. The food gets crushed by the gizzard muscle against these stones, mixing it with the digestive enzymes from the true stomach, and is then passed to the intestines.
So with no multi-stomach system and no cellulose-digesting bacteria, chickens can't extract much from grass, thus grass can not be the main food source for them. Is it still good for them? Absolutely! For a chicken, eating grass is like eating their vegetables, it's fresh and nutritious. But they do not get a significant amount of calories, protein or fat from it, which is why they need a concentrated food source. Think about how you would feel after a few days of eating just leafy green salad with no dressing! Since chickens are omnivores, they are quite happy eating just about anything but a grain ration mixed specifically for their nutritional needs is the best way to go if you want consistently healthy birds.
Bugs, of course, are another part of pasture that chickens are uniquely poised to take advantage of. And wow do they love bugs. Chasing down crickets and grasshoppers is a real passion of all chickens. However, there are just not enough bugs in a given space of pasture to fulfill a chicken's nutritional needs. Plus, since pastured chickens get quite a bit of exercise running after bugs, they actually have higher calorie needs than the average sedentary barn chicken!
Another very important factor is domestication. Humans have turned chickens into pretty different creatures from the wild red jungle fowl that they started from. Domestic chickens are much bigger, with a typical laying hen being around 5lbs, while a female jungle fowl is only a little over 2lbs. Jungle fowl only lay eggs with the purpose of raising a clutch and have access to the year round rich food sources of their jungle environment.
It is possible to feed chickens from a well managed compost operation. When feeding chickens on compost, it's important to keep in mind that they are mostly getting their nutrition from the various bacteria, fungi and invertebrates that live in an active compost pile, not the scraps themselves. However, this is only possible if compost is your main business, with chickens being a side line. The amount of compost required to keep the birds well fed is much more than even a medium sized market garden can go through in a year! And farms that do this often still supplement their chickens with grain and/or nutrient blends.
There are many people with small flocks of hardy heritage breed birds which, being a bit closer to their wild ancestors, are able to live off of bugs, grass and quality kitchen scraps, the trade off being a drop in productivity. But when you have 200 hens, all bred to be efficient egg layers, laying 6 eggs/week, withholding grain would be starving them. This is even more true for broiler chickens (birds bred for meat production), who are bred to efficiently and quickly convert calories to meat. They can't do that if they aren't getting concentrated calories from grain!
Goose Digestion
Ah, wait a minute, what's that you say? I couldn't hear you over the honking.
Geese are a bit unique in the poultry world. They do in fact thrive on JUST GRASS (at least during the summer). Their secret is that their gizzard is much more powerful than a chicken or duck gizzard, capable of crushing the cellulose in grass, so their digestive systems can access it. They also have a much longer intestinal tract than more omnivorous birds, which is populated with bacteria capable of breaking down fibers like cellulose. They are the cows of the poultry world! (Not sure about their methane emissions...)
Still want more details? Check out the links below for more info!
Further Reading
About our chickens:
Other Sources:
https://poultry.extension.org/articles/feeds-and-feeding-of-poultry/feeding-geese/
https://extension.umn.edu/dairy-nutrition/ruminant-digestive-system#the-small-intestine-1000461
https://en.wikipedia.org/wiki/Monogastric
https://en.wikipedia.org/wiki/Ruminant
Farms raising chickens on compost: