(a) The Mishnah rules that ...
1. ... one may not breed a Coy either with a Chayah or with ...
2. ... a Behemah.
3. ... if someone (who owned a Coy) bequeaths his son (see Tifefes Yisrael) his Behemah and his Chayah - he includes Vaday Behemos and Vaday Chayos, but not animals that are a Safek.
(b) The Rambam explains the words 'Chayaso u'Behemto' to mean - either his Chayah or his Behemah.
(c) ... in which case it appears - that if he specifically wrote both, then his son would indeed acquire them.
(d) And in a case where somebody points to a Coy and declares that he will be a Nazir if it is a. a Chayah, b. a Behemah, the Tana rules - that he is a Nazir, on account of the principle 'Safek Isur Lehachmir'.
(e) And the same will apply if he makes the same declaration - but on condition that the animal is either both a Behemah and a Chayah, or neither of them.
(a) In all other regards a Coy has the joint Dinim of a Behemah and a Chayah. This statement affects - three areas of Halachah (see Tos. Yom-Tov).
(b) Besides the fact that it requires Shechitah - it is also Metamei because of Neveilah in the event of its death and it is subject to Eiver min ha'Chai in its lifetime (see Tiferes Yisrael.