I’ve had friends ask me if my old horse gets jealous when I work with my new horse. I don’t know the emotional range of horses, but I do know that the old one knows when he had been retired.
My Dad used to ride a beast that I called the Magnificent SOB. His father and two of his half-brothers were World Grand National Champion Walking Horses. Jubilee (as everyone else called him) was a proud, powerful horse who became unsound after a front knee injury at age 21. Once Old Jub realized that he was not being pulled to be loaded into the trailer, he would show his displeasure by trying to take out his stall door and/or the barn wall. This lasted for a year until he accepted his retirement, but he never did stop giving us the evil eye while we loaded and unloaded the other horses. This lasted until his death in 2019 at the age of 31.
Moe never did act like he cared if he was groomed, petted or loaded into a trailer. He was laidback and aloof. Last year, at age 25, he was no longer sound for trial riding, so the search for a new horse began last summer. My new horse, coincidently named Big Moe, arrived in March. Old Moe saw the new horse being saddled for short rides around the farm and being loaded into the trailer. I don’t remember how soon it started, but when I enter the barn he is now at his stall window to see what I will do. He does not try to kick down any doors, but he has mastered the aloof evil eye.