Turn the horses east if you want a male foal
Of Africanus: on the generation of horses. If then you want a male to be born, turn the horses toward the east, so that as they mate, they face the sun; for the west produces the females, as the Mauretanian horse-herder related.
For also, as the account of all has it, it is believed that the male horses are yoked to the Sun and that the flame is driven by them, and they say that the females drive the Night. And justly: the Sun is male-making, and the Moon happens to be mother of a like-named nature.
Greek
3.3 Ἀφρικανοῦ· περὶ γενέσεως ἵππων Ἂν μὲν οὖν ἄρρεν τεχθῆναι θέλῃς, πρὸς τὴν ἀνατολὴν τοὺς ἵππους τρέπε, ἵνα μιγνύμενοι βλέπωσι τὸν ἥλιον· αἱ δυσμαὶ γὰρ τίκτουσι τὰ θήλεα, ὡς Μαυρούσιος ὁ ἱπποφορβὸς διηγήσατο. Καὶ γάρ, ὡς ὁ πάντων λόγος, τοὺς ἄρρενας ἵππους τῷ Ἡλίῳ ζεύγνυσθαι καὶ τούτοις ἄγεσθαι τὴν φλόγα πεπίστευται, τὰς δὲ θηλείας τὴν Νύκτα ἄγειν φασί. Καὶ δικαίως μέν· ἀρρενοποιὸς μὲν ὁ Ἥλιος, ὁμωνύμου δὲ φύσεως ἡ Σελήνη τυγχάνει μήτηρ.