Source: here.
1) The adhvaryu takes the last drink of water to the horse and offers
it with the formulae apAM peruH and agniH pashuH.
2) Then the yajur priests take fire around the 13 animal starting from
the kapi~njala that are tied along with the stallion and then release
them.
3) The horse is lead to a large piece of cloth spread on the ground on
which a piece of gold is placed. The the horse is strangulated by
another large piece of cloth bound around its muzzle by the shamitar.
4) The adhvaryu offers the paripashavayA oblations as the horse is being
killed and as it dies 3 oblations of ghee are made with prAnAya ;
apAnAya; vyAnAya + svAhA.
5) At the direction of the neShTA priest the royal ladies chant the
mantras beginning with namaste amba.
6) Then royal ladies move towards the horse and go around it 3 times
from left to right and recite the mantra gaNAnAntva gaNapatiM. Then the
go 3 times from right to left and chant priyAnAm tva. Then they go 3
times from left to right reciting nidhInAM tvA.
7) Then the emperor, the chief queen the mahiShi and the adhvaryu utter
the purificatory incantation for the dead horse. Then the mahiShi
recites Aham ajAni and lies besides the dead horse.
8) The adhvaryu then covers the two with the large sheet of cloth with
the formula svarge loke.
9) Then then phallus of the horse is excised and the mahiShi takes it on
her lap reciting the formula vR^iShA vAjI.
10) The emperor looks at the horse and recites the formula utsakthyA.
11) Then the adhvaryu, the brahmA, the udgAtA, the hotA and the sUtA
bard of the emperor, each, recite one of the five sexually explicit
formulae beginning with “yakA asakau..” directed at the royal ladies and
their brAhmaNa female companions. At the end of each hymn and they
recite the formula “haye cha haye asau —–” and utter the name of the
ladies. The kshatriya women and their companions reply by reciting the
sexually explict hymns paired with with the “yakA asakau..” series.
12) Then the mahiShI stands up and the priests in unison recite the
surabhimati hymns to purify their mouths.
13) 3 of the royal wives then mark the track of the knife cut on the
body of the horse with needles with copper, silver and gold bead heads,
reciting six mantras beginning with gAyatrI triShTup as they do so.
14)The knife for dissecting the horse has a gold handle.
15) The adhvaryu then starts dissecting the horse along the track laid
by the ladies while reciting 7 mantras starting with kastvA
AchChayati.
16) The fat is then scrapped off the visceral cavity of the horse. The
blood of the horse is collected in a separate vessel.
17) The animals slaughtered to prajapati, a bull, a male goat and a and
ram are also dissected similarly and their omentum is fried into
dumplings and havis cakes are also prepared to the north of the
AhavanIya fire.
18) adhvaryu and the hotA then engage in a dialog in vedic in the sadas
shed. Then the brahmA and the udgAta do the same. Then the former pair
of priests move to the west of the uttaravedi and do the same.
19) Then the adhvaryu picks up the silver mahimAn cup and filling it
with soma offers it entirely to indra with the yaste ahan chant.
20) Then the adhvaryu immolates the omenta of the animals with a
recitation of 20 mantras particular to these offerings to various devas
beginning with the combined indra and agni offering, other devas ending
with viShNu and then prajApati. Then there are offerings to the gotra
founders of the emperor and rudra.
21) Then the adhvaryu offers the second mahimAn cup soma pouring to
indra with the yaste rAtrau chant.
22) The rest of the meat of the horse is fried as dumplings in an iron
cauldron usually in the northern area.
23) Then he makes an oblation to the deity of the trees.
24) Then he offers each organ of the horse roasted as a dumpling to the
god to which it is designated along with the requisite yajur
incantation.
25) Then he recites the mA no mitra chant of two yajur AnuvAkas and
offers 16 ghee offerings. The last of these oblations is made to dyaus
and pR^ithivi.
26) Then the sviShtakR^it offering is made.
27) Then the offerings to the wives of the gods called the patnIsamyAja
rite is done. During this the womenfolk are shielded from the glimpse of
the sacrificial fire using the antardhAna plates.
28) Then comes the rite of the blood offerings, the rakta yAja.
29) In the rakta yAja the blood of the horse is taken in a copper pot and offered into the fire by streaming it through the dried trachaea of a nilgai and by using the hoof of a horse as a juhu ladle. The formula used is: agnibhyaH sviShTakR^idbhyaH svAhA.