One of the topics that was discussed in the sixth perek of Massekhet Yevamot was how the relationships that a woman has affect her ability to marry a kohen, and similarly whether she will be able to eat teruma – the tithes that are permitted only to a kohen and to members of his household. Although this topic has little direct connection to Massekhet Yevamot, nevertheless, the seventh perek, which begins on our daf, is devoted to clarification of this issue.
The basic rule of thumb with regard to eating teruma is that all members of a kohen’s household can eat, not only his wife and children, but also his slaves and even animals that he owns (see 22:11-13). This is true of animals that are kinyan kaspo – that the kohen has purchased and owns. If, however, the kohen was responsible for the animal, but did not actually own it, then he cannot feed it teruma. Thus, the Gemara on our daf quotes a Mishna in Terumot (11:9) according to which a kohen who rents an animal from another Jew who is not a kohen will not be allowed to feed it karshinei teruma, even though a Jew who is not a kohen would be allowed to feed karshinei teruma to an animal rented from a kohen.
Karshinim are a type of legume – vicia ervilia – more commonly known as Bitter Vetch. Like most legumes, karshinim have a high nutritional value and can be digested easily by animals. It grows in the winter and spring in lands around the Mediterranean Sea, and in Arab villages it is still grown as animal feed. Although its bitter taste makes it appropriate only for animals, in times of famine or for people who are in dire financial straights it would be prepared for human consumption, as well. Since it can be eaten by people, the obligation of terumot u’ma’asrot – of tithes – applies to it. Still it was usually fed to animals belonging to a kohen.