When males fight for dominance, they run at each other, rear up on their hind legs, and clash their horns together. These horns can weigh up to 30lbs and are made entirely of keratin, the same material our hair and fingernails are made of. Growth lines on the horns are often used to determine the age of the sheep. The horns grow more during times of plentiful food such as spring and summer and grow less during winter, creating distinct grow lines. A fully mature ram will have horns that curl all the way around back to his eyes, also called a Full Curl. If this begins to impair his vision, he will break the tips off himself.