Both Exodus 12:21, from the Elohist version of the Passover, and Exodus 12:3, from the Priestly writer (#109-110), state that the sacrificial animal of the Passover must come from the flock. The Hebrew denotes a small goat or sheep.
The Priestly writer’s Passover legislation exhibits other differences as well. As would be expected from a text written by priests, at a later date, and to bring the Elohist Passover tradition inline with this priestly guild’s sacrificial traditions and beliefs, there is a heightened awareness and care for the preparation of the sacrificial animal. The animal must be an unblemished male of one-year old (12:5). “Unblemished” is sacrificial language denoting both the animal’s physical health and perfection—no spots, deformities, illnesses, etc.—and “ethical” purity. This unblemished one-year old male lamb is furthermore to be separated out from the realm of the profane for 4 days prior to the ritual. This type of language and care for sacrificial animals is only found in the Priestly literature, and we will encounter more of it when we get to the book of Leviticus. Neither the Elohist nor the Deuteronomic versions of the Passover rite speak of it in these terms and with this language. In fact, D has the tendency to secularize such festivals.
In the Deuteronomic version of the Passover rite, the Deuteronomist now allows for both sheep and cattle to be used as the paschal animal, with no care for the age or gender of the animal. “You shall sacrifice the paschal offering to Yahweh, your god—sheep or cattle—in the place that Yahweh shall choose to establish his name” (Deut 16:2). The selection of the animal now becomes standardized to include both small and large sheep and/or cattle.
Ordaining the Passover rite to be performed at “the place that Yahweh shall choose to establish his name” is also a huge deviation from the older Elohist tradition, while nonetheless presenting this as the Elohist tradition. We will look at this more closely when we get to the book of Deuteronomy.
The term צאן (tzone) means a sheep or goat of indeterminate age. It is also used to indicate a flock of goat/sheep. בקר (bakar) means cattle as in a collection of bigger critters, also known as a “herd”. So “you shall slaughter…as a pesach of the flock and the herd” does sound redundant to add “herd”, but I am not certain that this is a clincher that it means that the pesach is older, since all lambs are part of a flock.