It's harder to tell with him standing next to the morbidly obese lighter horse, but the darker horse is very overweight as well.
If these horses were skinny instead of overweight, would you feel as apathetic? Skinny horses conjure up more emotion than overweight horses, but it is JUST as unhealthy, if not more, to be overweight.
The darker horse in the back is going through a hormone inbalance, her body said she was pregnant milk and dropped stomach and all. She is on antibiotics to fight an infection as well as had a shot to level her hormones. That is why she is so large. She normally ISN'T like that, she is my horse the lighter one isn't. Though she is slowly skimming back down to her normal weight then she is getting back on exercize.
My friend is over, the owner of the gelding, I made her invest in a lunge rope and encourged her to start coming over daily to start exercizing him.
Have you had the dun checked for insulin resistance? That would be my first guess and it can mess up their coats like that as well. If that is your friends horse I would highly recommend her getting that checked because if the horse is IR, then he will have to be on a very strict diet to live a full and healthy life.