female sheep, ewe
牂 centers on a female sheep, specifically an ewe. The meaning is narrow and concrete, with no strong abstract extensions.
牂 combines 爿 (a bed or board) with 羊 (sheep), likely to specify a female sheep. The exact historical development is uncertain.
The left side 爿 suggests a resting place, and the right side 羊 is a sheep. Picture a ewe resting in the fold: 牂 is a female sheep.
For ソウ, imagine a ewe softly saying 'sou' as it rests: the sound 'sou' cues ソウ while the sheep rests.