It makes sense, then, that milk and products containing milk would be totally foreign food items to a bird that spends its time in the rainforests and jungles of the world. Birds eat seeds, nuts, fruits, vegetables, shoots, leaves, blossoms, nectar, flower petals and such. Nowhere in its natural environment would it ever be exposed to milk, cheese, yogurt or other products containing milk. It should also make sense that birds would not have developed the enzymes necessary to digest milk sugar, lactose.
What happens if a bird ingests milk or products containing lactose, the milk sugar? Since it doesn't have the enzymes necessary to digest lactose, it will often pass through the bird's digestive tract unchanged. Because it is a foreign sugar, it may draw fluids into the intestinal tract, resulting in diarrhea, if ingested in large amounts. Small amounts of milk and products containing lactose are probably not harmful to most birds.
Some milk products do not contain lactose, such as cottage cheese and other types of cheese. Generally, it is thought that it is safe to offer yogurt and cheese, although products that contain lactose are probably safe, if offered in small amounts. Interestingly, live culture yogurt does contain lactose when it is produced; however the live organisms in the yogurt consume the lactose, eventually removing the lactose entirely from the yogurt before it is consumed! Cheese products with onions or garlic in them are best avoided, because of the risk of Heinz body hemolytic anemia.
Many bird owners, it seems, enjoy spending time in the mornings with their pet birds. Often, a bird may want to share breakfast with an owner. We get many questions about whether or not it is alright for a bird to share a little cold breakfast cereal and milk, or oatmeal made with milk. If the bird is just ingesting a small amount of milk, this should pose no problems for the bird. But, caffeinated morning drinks should be off-limits to birds, with or without milk added.
There is some concern about some soft cheeses potentially causing crop impaction in birds. While I have never seen this occur (and I do feed my two greys and Meyer's parrot mozzarella cheese almost every day), this may be more related to the volume of the soft cheese being consumed than anything else. So, when choosing foods to offer to your bird, use common sense, and don't provide one type of food in abundance or to the exclusion of all others. If you have any questions, always ask your avian vet for advice related to diet tailored for your specific bird.
I have been asked about the possibility of giving a bird a commercially available product developed for lactose-intolerant humans. The answer to that question is a resounding NO. The two compounds that lactose is broken down into by these products are toxic to birds!
While dairy products can provide a bird with necessary nutrients such as calcium and vitamin D3, we should choose carefully what items we offer to our pet birds, to ensure their safety. When in doubt, check with your avian vet regarding safe and appropriate food items to share with your bird."
Because they cannot digest the lactose in milk. They are naturally lactose intolerant. Which is silly, because lactose intolerant people eat yogurt fine since the lactose has been processed by the yogurt bacteria.
yogurt is obviously not a natural food for chickens, but it is great probotics. and can do wonders for the health of a chicken (or human, or dog, or...).
i think it'd be great to share other alternatives for calcium, vitamin D3, and the B vitamins as well. Do you have any?
also, to be fair, the chicken food you buy at your local co-op is NOT a natural food for chickens either.
edited to add:
raw milk is not only ok for chickens, but has been used for, well, forever, by farmers. they would/will give their left over raw milk to the chicks as to not waste. also, raw milk is used to treat disease. please note 'raw milk' is NOT the same as 'pasteurized milk (the milk you probably have in the fridge)'. raw milk works in a similar way as yogurt and cheese - - considering you leave it out for a day or two.
pasteurized milk is not good for most animals. they cannot digest it. it's not going to kill them on the spot - but it may make them ill.
My flock have been getting goat milk since I got them at 3 days old, other that are hatched here start off with it when they start eating. I mix fresh goat milk with their crumbles every morning or they get goat milk yogurt mixed with their crumbles. I have never had a problem with my chickens and goat milk. No diarrhea, no sickness.....just nice strong eggs shells and happy hens.
I have been feeding goat milk to the chickens since I got my first milkers (30 years ago?) I have never tried cows milk though.
Plain yogurt is fine for chickens as a source of probioitics and to aid in recovery from coccidiosis. The bacteria make it different from just any old dairy product, but honestly, as long as you're not giving them milk and ice cream on a daily basis, I don't think much harm would be done. In fact, raw milk was long considered a treatment for coccidiosis. And when I could afford buttermilk (who can anymore??), I gave them buttermilk and raw pumpkin seeds as a low level wormer.