There is no scientific data or evidence indicating a correlation to feeding of bermudagrass hay and impaction colic. You need to be certain that you are feeding a good-to-high quality hay by having a laboratory analysis done to determine nutrient levels. You must also visually inspect and smell hay to make sure it is free of mold. The stage of maturity of hay at time of harvest will have more to do with the amount of lignin in bermudagrass. Lignin is an indigestible structural component of forages that is not digested by the horse. The more mature the plant at cutting, the higher the lignin content and the lower the digestibility.