Organic fibers are grown using methods and materials that have a low impact on the environment. Organic production systems replenish and maintain soil fertility, reduce the use of toxic pesticides, synthetic fertilizers and genetic engineering. Organic animal-based fibers must be produced in accordance with standards for organic livestock production. Livestock feed and forage must be certified organic, and the use of synthetic hormones and antibiotics is prohibited. Third-party certification organisations verify that organic producers use only methods and materials allowed in organic production.