Castration

The word שור in Hebrew can refer to an ox or a bull, but which animal is the protagonist of the celebrated law of שור נגח, “the goring bovine”? 

Jewish law prohibits the gelding of animals based on its interpretation of Leviticus 22:24. Is this what the Torah means? Why might the Torah have prohibited this, and how could the prohibition function in an agrarian society dependent on draft animals?