The cow horns relate to biodynamics, developed by Rudolph Steiner at the turn of the 20th century.
Compost tea in this context is aerated compost tea, which is made by adding a high quality compost (such as vermicompost) to water and forcing air into water. The oxygenated water also contains some sugar, usually in the form of molasses. This water then causes a bloom of the beneficial bacteria and fungi present in the compost.
The resulting compost tea can then be applied to soil or plant surfaces to inoculate them with the microorganisms needed for optimal plant health.
Podcast 15: Compost Tea with Kevin Titus of Red Fox Organics