One of the major problems we see in horses and other equines is laminitis, and this is mostly due to eating pasture grass with a high concentration of carbohydrates. The intake of non-structural carbohydrates increases the glucose level in the blood, and this causes an increase in insulin. That increase causes laminitis, so many of these horses have to be taken off pasture. However, it is also not a good idea to stall these horses and so you have to turn them out in a dry lot, and many people do not have the facilities to do that.
The researchers at North Carolina State studied the effects of mowing the grass and the effect that would have on insulin and glucose levels. The pasture used for the study consisted of tall fescue, and the tall height of the plants were 12 inches and about 6 inches tall after mowing. All horses used in the study were healthy with no evidence of equine metabolic syndrome, and horses were interchanged weekly on different pastures. Results indicated that horses did eat less when the grass was shorter, but they still ate enough to get the amount of forage needed for their requirements. Some horses did lose weight on the mowed pasture.
However, we have to be careful looking at this study because although the carbohydrate intake was less in the mowed pasture, that doesn't mean it would be low enough to prevent laminitis in an insulin-resistant horse. Also, remember that this study was done using only fescue. If you have an insulin-resistant horse, this study doesn't mean you can just mow the pasture and turn your horse out because the horse could still develop laminitis from the shorter grass.