Related על עבודה זרה 2:11

They do not nurse from clean animals on holidays [and one needn't mention on shabbat. Abba Shaul says: they used to nurse from clean animals on a holiday.] A woman should not release milk from her breasts or express milk into a cup or dish in order to nurse her child. They do not nurse from either a gentile or an unclean animal, but if it is a matter of danger (to life), it is permitted, in that there is nothing that should stand before saving a life except for idol worship, forbidden sexual relationships, and shedding blood.