This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
牨 combines 牜 (cow) with 亢, but the exact historical development and original meaning are uncertain.
A cow 牜 beside 亢, a shape that might suggest a strong neck or throat. Without a clear meaning, picture a sturdy bull with a thick neck.
For コウ, imagine a cow with a strong neck letting out a low "koh" sound: koh -> コウ.