I consulted with Dr. Lori Warren who is an extraordinary equine nutritionist here at the University of Florida. Here is her reply:

Whether wheat forage/hay is suitable for horses depends on the wheat’s stage of maturity at cutting. If the wheat is cut and baled before dough stage (ie, before seeds have formed) or at early dough stage, it can be a very nutritious forage/hay for horses. However, one issue with cutting wheat during an earlier stage of maturity is that it can have high levels of nitrate. Although there isn’t an established level known to cause harm in horses, if the cereal forage cannot be fed to cattle for nitrates (0.4% nitrate-nitrogen, or 1.77% nitrate), it is also not recommended for feeding to horses.

If the wheat is cut after seeds have formed, it not only loses nutrition but presents some problems for horses. Specifically, the small wheat seeds are difficult for horses to chew and can form “doughy” balls in their stomach that cause colic. The beards on mature wheat seedheads can also cause dental issues if they become embedded in the horse’s mouth.

If the wheat is cut and baled after harvesting the wheat seeds for some other purpose, what is essentially baled is the straw – this is not necessarily harmful to horses, but they will need supplemental nutrition as the straw would not meet their nutrient requirements.

So ultimately there are several factors – most related to stage of maturity of the wheat – that influence whether the wheat forage could be safely fed to horses.