yearling
An animal that is about one year old.
A yearling is an animal that is one year old, or in its second year of life. The word is most commonly used for horses, cattle, deer, and sheep. A yearling horse has lived through its first year and is now learning skills like being ridden or pulling a cart, though it's still too young for heavy work.
Farmers and ranchers pay close attention to yearlings because this is an important stage of growth. A yearling is no longer a helpless baby needing constant care from its mother, but it's not yet a fully grown adult either. Think of it as roughly equivalent to a human preteen: gaining independence and strength, but still maturing.
When you see a graceful young deer bounding through the woods in early summer, that's likely a yearling that has grown strong enough to keep up with the adults but hasn't yet reached its full size.
Ranchers sometimes hold yearling sales, where they sell young cattle that are ready to be raised by other farmers. These yearlings have been weaned from their mothers and are old enough to thrive on their own.