Why does it say "Alecha Horagnu Chol ha'Yom"?
Gitin 57b #1: It hints to a boat with 400 boys and girls being taken to Romi for sexual exploitation. They realized this, and jumped into the sea [to die].
Gitin 57b #2: It hints to a woman and her seven children. (The emperor asked each child to bow to idolatry; after all seven were Moser Nefesh, she killed herself.)
Gitin 57b #3: It refers to circumcision, which we do on the eighth day (sometimes babies die from it).
Gitin 57b #4: It refers to Chachamim who demonstrate slaughter on themselves (this can prompt death).
Gitin 57b #5: It refers to Chachamim who give their lives for learning. "Zos ha'Torah Adam Ki Yamus b'Ohel..." (Bamidbar 19:14) - words of Torah last only in someone who kills himself (forgoes all other interests) for them.
Radak: We are killed for unity of Your name. We refuse to deny You, and they kill us for this. "Kol ha'Yom" is constantly.
Malbim: Also the Anusim who renounced Judaism at the time of Shmad 1 were killed afterwards; they investigated them and found that they covertly guarded Torah.
I.e. the Marranos, who openly acted like Notzrim at the time of the inquisition in Spain (starting in 1492), lest they be killed.(PF)
What is "ka'Tzon Tivchah"?
Rashi: It is like flock [destined] for slaughter. Radak - they are not to graze and stay alive.