You know, horses are like humans~ each one is the same, yet different. Our digestive systems,etc. What one can eat the other cannot. we just have to learn what our individual horses can handle,in eating, stress, environment,work,nervous systems,etc. We have to stay diligent and research and monitor our beloved mounts.
My gelding had no problems with oats~They almost killed my mare.
Blessings to you all.May you find what works best for you.