Parashat Tetzaveh discusses the various offerings and sacrifices that are to be regularly given. Of these, two animal sacrifices must be enacted every day of the week:
Thus you shall do to Aaron and his sons, just as I have commanded you. You shall ordain them through seven days, and each day you shall prepare a bull as a purification offering for expiation; you shall purge the altar by performing purification upon it, and you shall anoint it to consecrate it.
Now this is what you shall offer upon the altar: two yearling lambs each day, regularly. You shall offer the one lamb in the morning, and you shall offer the other lamb at twilight. (Exodus 29:35-39)
(This is taken from the 1985 JPS translation, which is what I had been working with.) How does this work with the halacha around Shabbat? As far as I can tell, that it is a burnt offering does not matter, as the fire of the altar is never ignited or extinguished, but how about preparing the animal for sacrifice? Isn't butchering a melacha?