Caviar is considered a great delicacy, and while not from horses, it's the female half of the sperm + egg equation. I'm sure many of the people who have posted their utter disgust at the idea of consuming horse semen regularly consume eggs from chickens. Our delicious "milk" that we buy in the grocery might not sound so appealing if we weren't culturally used to drinking it and someone came up with the idea of drinking 'cow udder secretion'.
Not that I'll be consuming horse semen anytime soon, but it's interesting the way our cultural norms bias what we find disgusting versus what we consider to be a treasured delicacy.