Cow horn 
Cow horn, the keratin sheath covering the bony core, obtained from the slaughterhouse.
Characteristics
- In biodynamics it is the casing for preparations 500 (horn manure) and 501 (horn silica).
- Tradition prefers horns from cows that have calved.
- A clean horn can be reused for several years.
Role in the preparation: It is filled with cow manure (500) or ground quartz (501) and buried over winter or summer.
Caution: Source it from an approved slaughterhouse or farm and follow local rules on animal by-products.
Sources: Biodynamic agriculture - Wikipedia · Horn (anatomy) - 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.