An udder is an organ formed of two or four mammary glands on the females of dairy animals and ruminants such as cattle, goats, and sheep. ... This helps prevent bacterial infection, and reduces irritation during milking by the cups, and so the cow is less likely to kick the cups off.

Why do cows have so many udders?

Not only do they need a whole lot of milk, but because they need space in their abdomen for a rumen, they don't really have space for a great big milk cistern in there. This is why they have developed an udder: there isn't space for all the necessary milk internally.

Do cows have udders when not pregnant?

All breeds of cows can have udders, but visible udders are only present in female cows who are either pregnant or have already had a calf.