This is a good example of a word having different meanings in different contexts.

Animals giving milk are producers in the way people usually use the word. The way we biologists use the word when we are talking about food webs or food chains is different. Then we mean living things that do photosynthesis.

Producers have to be plants, or algae, or one-celled things that do photosynthesis. So a mother cow produces milk, but she uses the energy in the food she eats to get that energy. Plants use the energy of the sun.

That's an interesting question. I'm sure lactating women aren't considered 'producers' in any sense, because lactating women aren't usually 'considered' at all. [I just heard Gloria Steinem speak in San Francisco this week, so I'm extra sensitive to such matters at the moment!]

An online dictionary defines 'producers' as 'people, companies, or countries that...'; but I see that, of course, producers are also organisms [and movie makers].

Looking at the definitions of organisms that are 'producers,' I see that they all make food out of energy sources that are not food, such as sunlight [phosynthesis by green plants and green bacteria] and inorganic chemicals [chemosynthesis by some bacteria].

So lactating animals aren't producers because they produce milk, in the same way that they aren't producers because they 'produce' meat.

That reminds me of guinea pigs, which have been compared with cows - they both eat grass and can be eaten for their meat! But not my guinea pigs, who eat grass but will never be eaten..

'Producer' in ecology is like 'consumer': it has multiple levels. Plants are primary producers, meaning that they fix biological energy that was previously not biological. Anything that eats plants and builds up a body is a secondary producer, just as it is a primary consumer. Any animal is thus a producer at some level, because all animals' bodies get eaten when they die and decay if nothing else, but apart from the few photosynthetic animals or chemosymbiotic animals that contain algae or bacteria that make their own food, animals are never primary producers.

This is a fun question. Producers are organisms that create food, so surely lactating animals should be included, right? Even though this seems to make sense, it is actually wrong. You have to think about where lactating animals get the material to make their milk. Let’s use cows for an example. Cows eat grass and their digestive system breaks down the grass into its most basic components called macromolecules. The cow’s body then takes these macromolecules and uses them to create milk along with everything else in its body.

Now think about this as opposed to the grass the cow is eating. The grass is using energy from the sun to power photosynthesis where carbon dioxide from the air will be converted to solid plant mass. While the cow is using organic carbon (here meaning carbon that came from another organism), the grass is using inorganic carbon (carbon not from an organism like carbon dioxide in the air). Only animals that use inorganic carbon are considered producers because they literally produce food from thin air. Thank you for the question!