mane, neck bristles
鬃 centers on the coarse, protective hair along an animal's neck: the mane or neck bristles.
鬃 combines 髟 (hair) with 宗, which likely contributes the sound. The character specifically refers to the mane or bristly hair of an animal's neck.
The top 髟 is the hair component, and the bottom 宗 looks like a sturdy neck with bristles standing up. Picture a horse's neck with a thick mane flowing down from the hair radical.
For ソウ, imagine a horse's mane blowing in the wind as it runs through a field of 草 (そう, grass): 草 -> ソウ, and the mane rustles like the grass.