This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
牻 combines the cow radical 牜 with 尨, which likely contributes the sound. The exact historical development is uncertain.
The left side 牜 suggests a cow, and the right side 尨 looks like a shaggy dog. Picture a spotted cow and a shaggy dog standing together, but the meaning is unclear.
For ボウ, imagine a bow tied around the cow's neck: bow -> ボウ, and the cow is spotted like the reading まだら suggests.