Sound! Sound? Sound.

[QuarterHorseMac]

Whats sound? "the clydsedale is an exceptionally sound horse."

[bexj]

Sounds like (pardon the pun - groan) in this context, sound refers to to the type of horse in that it is solid, good to do (maybe a UK phrase sorry), doesn't tend to suffer from health or eating problems, good temperament etc etc

Otherwise sound can mean a horse that is not lame.

Hope this helps