If you don't know who owns the horse, who else are you going to call?
You drive around and FIND out who lost a horse.
Several years ago I spotted 2 loose ponies just a trotting past my place.
I saw they had stopped just up the road to eat, I grabbed a halter and walked up to them leading one back to my place while the other one followed.
I went around the area and low and behold I was told it belonged to people several miles away. They were called and came with their trailer to pick them up, happy that I got them and they were safe.
And One of my horses got loose one night, I drove around asking people had they seen a pony on the loose, In one car I asked said around and follow me.
I did and he had put my miniature in his outdoor dog kennel.
I thanked him, it was only 1/2 mile away in the middle of winter. I drove home he brought me to his place and I led the horse back home once again.
And another time two of my mini's got out and was a mare and her baby in the front yard close to the road, my mailman came by, stopped and put them back in their pens~!
I thanked him very much the next day.
SO you see in ALL of these cases not once was a animal control person called.~!
And one more case, I was driving the backroads and saw a stern was loose I knew it had to belong to the fame I had just passed, I drove and got ahead of the steer and made him turn around, when he got close to the somewhat long driveway I got in front once again and he turned down the drive.
I Stopped and blocked the drive as I could see the fame getting a hold of him and when he did I waved and went on my way. Good friendly neighborly gestures like this pays of in spades later on.