Wagtail
Horse servant
Well I have one in my present herd, she will not touch haylage but will eat hay quite happily. She is also very aged (32) and can drop off dramatically over winter if I don't keep an eye on her.
I agree with Spaniel that horses are actually designed to drop weight over winter and the fact that some uninformed owners think this is wrong is one of the reasons laminitis is so prevalent today.
I don't think it is so much a matter of design as being able to 'cope with' fluctuations in food availability. As I said earlier, dogs will dramatically drop weight in the winter if they live wild. Why do you not then cut down their food in the winter? They too are 'designed' for it.
I believe that horses (and dogs) are healthier if they maintain a steady ideal weight throughout the year.
ETA Laminitis is so prevalent because people put their horses out onto pasture that is too lush.