For ten points, name this animal that says "neigh".
The opening line of the Brhadaranyaka Upanishad states that this animal's head is the dawn before going on to compare each of its body parts to something and telling a story about death transforming himself into this animal. Uchaishravas was a flying animal of this kind that emerged from the churning of the milk ocean and was eventually acquired by Indra. The ashvamedha ceremony involved mimicked copulation between this animal and the queen and functioned as a kingship ritual that ended in this animal's sacrifice, a key ceremony in Vedic and Proto-Indo-European religion whose sacrificial victims would be selected for prowess in racing. For ten points, name this animal that says "neigh".
The opening line of the Brhadaranyaka Upanishad states that this animal's head is the dawn before going on to compare each of its body parts to something and telling a story about death transforming himself into this animal.
{horse} [accept: {ashva} from an {adhvaryu priest} before “{ashvamedha}”]