From: Rabbi Mordechai Leib Winkler
To: Rabbi Yoshia P.P.
The responsum discusses whether it is permissible to transgress a Rabbinic prohibition (Shvut) on Shabbat due to the suffering of an animal, specifically challenging the view of the Pri Megadim that Tza'ar Ba'alei Chayim on Shabbat is a Torah prohibition.
Source: Orach Chayim II §62