Giraffes or elephants can have young, but a litter (singular) is the group of very small animals that something like a dog, cat, or mouse has. A mother cat would protect any single one of its young, not just the group of them, the litter.
Theoretically, you could do so, but it would change the meaning of the sentence a bit. A litter is a group of young animals. A bear usually has only one or two cubs. The cubs are not called a litter, because there are so few of them. But you don't want to threaten them because the mother will attack you.