Straight from the horses mouth

From the highest authority.

In horse racing circles tips on which horse
is a likely winner circulate amongst punters.
The most trusted authorities are considered to be those in closest touch with the recent form
of the horse, i.e. stable lads, trainers etc.
The notional 'from the horse's mouth' is supposed to indicate one step better than
even that inner circle, i.e. the horse itself.

"Ro i land - Pull through"