Q: What exactly about the Hebrews and their sacrifices is “detestable” to the Egyptians?
A: Your question is one that puzzles scholars and commentators. It would seem more logical that the Hebrews would find making sacrifices in Egypt detestable – but Moses gives the impression that the Egyptians would find the Israelite’s sacrifices detestable:
Since the text is silent about the exact meaning of Moses’ concern, I’d be very hesitant to try to give a definitive answer to your question.