STEINER'S PROPOSITION:
Cow horns (in contrast to the antler's horns) retain formative astral-etheric forces and send them back into the digestive system. These forces are preserved and can be utilised in cow manure which is permeated with nitrogen-bearing forces and oxygen-bearing forces. Preserving these forces in a certain way and applying them has an enlivening and astralizing effect on the soil. In contrast to water soluble fertiliser which only effects the watery part of the soil, horn manure also impacts on the earthy, mineral component of the soil. Manure is stuffed into a cow horn and buried. In this way the a&e forces are preserved and because the horn is surrounded by the Earth, these forces are further enlivened.
HOW TO MAKE 500 ACCORDING TO STEINER:
Take the manure, in whatever form available, and stuff it into cow horns and bury it in the ground (0.75m - 1.5m). The soil should not be too sandy or clayey. The horns are buried during the entire winter, the season when the Earth's forces are inwardly directed. 
At the end of winter, the horns are dug up and the manure is taken out. The slightly sweet smelling content contains immense a&e and life-giving forces. Diluted with water and thoroughly stirred in a certain spiral way for a certain period of time the manure is ready to be applied to the land.
ESOTERIC COMMENT:
The cow horn preparation preserved Sun forces that work through the planets nearer the Sun, causing germination, root development and plant growth. The spiral stirring is of significance as it echoes the rhythmic and spiralling nature of all life. Vortexing stirring in one direction echoes the 'Winter Sun' while the other direction relates to the 'Winter Sun'. 
PRACTICAL FARMING CONSIDERATIONS:
Prep 500 takes on the characteristics of the soil in which it is buried. Its best to make the preparation on the land where it will be used with dung that has been collected from the farm itself. 
Quality of preparation: Can be checked by Chromatography. 
Smell, feel and look are also important. 
Dung must come from healthy animals feeding on a good mixture of grasses.
Collect dung on the same day the horns are filled.
Location of the burying pit: 
Find a well drained spot where BD preps have been applied for some time.
Pad the pit with mature BD compost. Fertile topsoil layer is best. Size of pit: 2 x 4m. In non-frost condition the pit does not need to be much deeper than 0.4m. 
Cow horns:
Medium sized horn sources as local as possible are best. (Jersey, Milking Shorthorn, Friesian), Mature cows are preferred to heifers. Do not use bullhorns.
Method:
Fill cow horns. Place them into pit with open ed down to ensure drainage. The horns should not ever be flooded with water. The pit should not ever become dry. Give each horn a bit of space. Back-fill the pit gently. Horns should not be in the ground for longer than six months. Check after four months.
What can go wrong:
Worm can eat up the cow dung. To discourage worms place a good quantity of raw compost on top of the pit. Keep the pit free of weeds and grasses so that no roots can grow into the horns.
Timing:
Best time to bury in Australia is April / May. Best time to dig up is September / October. Watch the soil and make sure it does not dry out.
Lifting:
The 500 should be slightly loose and have a sweet smell without any suggestion of cow dung smell. Sometimes there can be a white or pink fungus growth. This is of no concern. Store the 500 in glazed earthenware jars in a cool place. Lid should be loose fitting as the 500 needs to breathe. Well-stored 500 will last up to three years. 
HOW TO APPLY 500:
Use rain water. Run it over a flowform for a couple of hours. Avoid using plastic containers. Dissolve the 500 in the water. Stir with your hand or a stick. Create a good vortex that reaches right down to the bottom of your container. Once you build a good vortex, crash it by reversing the stirring direction. Change direction three times in a minute. After about 30 minutes the water changes to a more slippery nature and stirring becomes easier. Stir for about 60 minutes.
When and how often:
Twice a year; in spring and autumn. Moon phase: always apply in the descending moon phase. Time of the day: early autumn: about 4pm; late autumn: about 1pm. Early spring: 2pm; late spring: after 5pm. Light rain can help especially when the grass is long.
How much to use and how to distribute: 25g stirred into 13 litres of water will cover 1 acre. Apply no later than one hour after stirring. Use natural brush to spray while walking the land. 

Additional reading: (open in separate window)
A personal experience by Steven Guth
Chemical Processes Underlying Horn Manure (pdf format)
I farm biodynamically - why