Pap – one dictionary definition of the word in general is “bland soft or semi-liquid food such as that suitable for babies or invalids.”
Koala mums don’t have the luxury of a supermarket and kitchen to prepare those first baby meals for their joey of course.
The koala digestive system is unlike that of most other animals. We know that koalas eat leaves. Do you also know that a joey drinks mum’s milk and nothing else for around 6 months while developing in the pouch?
Most animals that digest leaves and grass have 4 stomachs, and these animals are called ruminants. Cows, sheep, goats, giraffes and kangaroos are some of the most common ones you might think of.
However, some animals that eat leaves have only one stomach, and they use a really big caecum to do this (that’s the appendix in us, which is tiny). They are called ‘hindgut fermenters’. Horses, rabbits and koalas are common animals you know that are in this category.
The caecum and the large intestine are filled with microbes that turn it into a big fermentation vat. This fermenting happens in the extra stomachs of ruminants and they are also called ‘foregut fermenters’.
It’s the microbes that are of most interest here. Other articles will cover more about digestion. Joey has been living a very sheltered life inside mum’s pouch, and has been drinking only her milk. The microbes joey needs to digest leaves are not found in the leaves, so joey needs to get them from somewhere. A goat kid will begin nibbling dirt within hours of birth and so begins to get microbes into their digestive system. Not the case for the koala, as joey is still very fragile and high up in the treetops.
So mum has to provide the microbes joey needs to ready the digestive system for those tough eucalyptus leaves.
Joey knows when the desire to eat begins, and puts its head out of the pouch and begins to nuzzle around mums cloaca. (koalas have a single opening like birds and so it has the same name as we use for birds) This nuzzling and licking stimulates mum to begin to secrete a pasty liquid directly from her caecum for joey to eat. Koala faeces is shaped into firm pellets, but pap is a pasty semi-liquid. It is really quite similar in texture to a puree made for a human baby just starting to eat. However the reason is to kick start the hindgut in the fermentation process rather than to provide nutrition. You could say, pap is a probiotic infusion.
We usually say that pap is a special faeces, but it is actually contents of mum’s caecum. Probably not a big distinction for most people, but there is a difference. Mum’s only produce the pap for a week or two at most while joey stimulates her. Joey knows when it is no longer needed as joey starts to feed on leaves and is able to easily digest them.