What animal is primarily raised for its fiber in agriculture?

Sheep are primarily raised for their fiber, which is most commonly wool. Wool is a highly valuable natural fiber that comes from the fleece of sheep, and it has a wide range of applications in textiles and clothing due to its insulating properties and moisture-wicking capabilities. The production of wool is an important aspect of sheep farming, and various breeds are specifically cultivated for the quality and quantity of their fleece.

The other options represent animals that have different primary agricultural focuses. Cows are mainly raised for milk and beef, pigs are primarily raised for pork, and horses are generally kept for riding, work, or companionship rather than for fiber production. This is why sheep stand out as the correct choice when considering the animal chiefly raised for its fiber.