to hear straight from the horse’s mouth = to receive information from someone who knows the facts

I either heard them from friends or straight from the horse’s mouth, which in this case was my father.

To Hear Straight From The Horse S Mouth

 

If wishes were horses… = is used to say that it is useless to wish and that better results will be achieved through action

— If only I got this job!

— If wishes were horses…

If Wishes Were Horses

 

Hold your horses! = to hold on, to wait; to stop and consider carefully their decision or opinion about something

Irritably — she really wanted that cup of tea; she was growing as bad as the British — McAllister turned off the gas ring, blew out the match, and walked to the front door, grumbling to herself, Hold your horses, I’m coming, I’m coming, when another urgent series of knocks sounded.

Hold Your Horses

 

to flog/beat a dead horse = to waste time trying to do something that will not succeed

Do you think we will pull the project off or am I just flogging a dead horse?

To Flog A Dead Horse

 

to eat like a horse = to eat a lot

She eats like a horse and never gains an ounce.

To Eat Like A Horse