Conversation so far:
What was Seattle Slew's heritage?
Seattle Slew was a dark brown colt with a small white patch of hair by his left rear hoof bred by Ben S.
Castleman.
Did he show signs of his greatness early on?
CANNOTANSWER.
When was his first race?
CANNOTANSWER.
Who were his parents?
He was sired by Bold Reasoning who won the Jersey Derby and Withers Stakes in 1971.

Question: Who was his mom?
Self-contained rewrite: Who was Seattle Slew mom?