Hello Trudy,
The answer to your question, I do not know.
But I assume the "Jitals" of the Khwarezm Shahs were a following up of the Jitals of the Hindu Shahis, de famous Horseman &
Bull Jitals.
One could expect a
bull on a hindu coin, as there are religious reasons to. The
bull Nandi was the mount of Shiva and in
India the Nandi temples and shrines are countless.
With their arabic script, I doubt the Khwarezm Shahs
had any religious reasons to put Nandi on their coins. Maybe the
bull is just there to mark the coin as a "Jital".