He works twice as hard as the mares, but he is fatter than either of them. I've spent a few days thinking and a few days watching them. This is what I have come up with:
1. Both mares are bigger than he is, but I feed them all the same. Probably ought to change my feeding habits.
2. When the girls run around because a school bus drives by, John stands there and eats.
3. When the girls go visit the other horses over the fence, John stands there and eats.
4. When the girls run to the gate because I pull in the driveway, John stands there and eats.
5. I think four reasons is enough. Not much comes between John and his hay, so I guess I better come between John and his hay :)