If you're talking about what I think you're talking about it is neigh
A horse makes many vocal sounds including:
Whinney
Nicker
Snort
Grunt
Moan
A horse makes a nay sound.
A whinny, neigh or nicker.
Neigh!!!
Heat.
WHINNY or NICKER
The sound that a horse utters is called a neigh.
The word would be "sound".
Whinny. (informal, "neigh" (pronounced "naye"))
I believe it is called "blow."
Horses.
COS THE BODYS IMUNE SYSTEM MAAKES IT DAT WAY I MAY BE WRONG
There's a type of training you can use with your horse. I think it's called sounding. It also depends on what the horse is afraid of. Cherry Hill wrote a book called "How to Think Like a Horse" that touches on how to make your horse become sound. Rewards for horses are key to training!
It means that there is nothing wrong with the horse's hooves. A horse is not sound if it has thrush, wind puffs, etc.
Train it.