Quote:
All birds are lactose intolerant. Lactose is a compound sugar that is unique to mammals. Only mammals and some bacteria can produce lact
ase, the enzyme necessary to break lact
ose down into glucose and galactose (simple sugars that nearly all life can digest). Normally as mammals ween off milk, their genes that are responsible for making lact
ase are turned off as they aren't supposed to still be drinking their mother's milk. Humans that are
not lactose intolerant have a beneficial mutation that causes the lact
ase gene from getting turned off. That's why nearly everyone who is not of european descent is lactose intolerant.
In nature, birds do not depend on mammalian milk for nutrition so there is no biological need to evolve the ability to digest lactose. As a result they are all lactose intolerant.
That said, we give our ducks cottage cheese once in a while as a treat (cottage cheese is generally lower in lactose than milk). Like in the case of lactose intolerant people, a small amount of lactose for ducks generally shouldn't cause any problems. Like almost all things in life, the key is moderation. A small scoop of ice cream doesn't bother me at all, a few scoops tends to bother the people around me, and eating an entire carton would make me curse the inventor of ice cream.
Also, it's a good idea to keep an eye on your duck's poop whenever a new treat is introduced to help ensure they aren't having any problems with it. Too much lactose in theory could cause diarrhea and/or gas (appear as foamy poop).