Benefits:
Grass hay is lower in protein and energy than legume hay, but it is also higher in fiber which can make it a good choice for many horses. Since it is less nutrient-dense than legume hay, horses have to eat more grass to fill their bellies, which makes grass hay a good tool for keeping a stall-bound horse from getting bored.
Downsides:
Grass hay alone may not be enough to sustain a hard-keeper horse, a growing horse or a pregnant or lactating mare. Additionally, horses in heavy work will need more energy and nutrients than can be found in grass hay alone.
Best for:
Easy keepers, horses in light work, retired horses, and as a tool to help buffer stomach acid and add roughage without adding too many calories or excess protein. Providing nutrient-light, bulky grass hay can closely mimic the horse’s natural pattern of grazing slowly and processing fibrous feed equally slowly and steadily through the digestive system.