I make horse treats all the time, out of whatever is in the kitchen. As a matter of fact, I made some today because my husband was going to throw away some old cereal.
I dump cereal, oats (like you make oatmeal out of), flax seeds, shredded carrots, chopped apples or any other veggies or fruits, some eggs, oil, molasses or honey or corn syrup into a big bowl & keep adding wet stuff til it seems about right. You know, like cookie dough consistency. Just add whatever you have on hand. Sometimes mine have a lot of ingredients, sometimes only a few. But always some kind ofcereal &/or grain, oil & eggs. Then drop onto a cookie sheet or mash it into a big pan (for bar cookies) or a muffin or mini muffin pan. Bake at 350 til they seem set enough (depends onthe type of pan you use. Cool completely, cut into bars if needed, then store in a large ziploc baggie or container.
If you're not going to the barn for a few days, store it in the freezer. Mine are different every time, depending on what cereals and other ingredients I have on hand. But the horses always love them!