Sheep wool 
Unwashed or waste sheep's wool (low grades, shearing leftovers).
Characteristics
- Made mostly of keratin, a protein rich in nitrogen and sulphur.
- Greasy wool also contains lanolin (wool fat).
- It breaks down slowly in soil, over several months.
Role in the preparation: It is used chopped as a mulch or as a slow-release nitrogen-rich material.
Caution: Use wool free of dyes and sheep-dip products; in the EU raw wool is a category 3 animal by-product.
Sources: Wool - Wikipedia
Documentary information: this is neither a recommendation for use nor a plant-protection or veterinary claim. Check your country's regulations before any use.