This time of year you should be careful putting a horse on a diet. A 
reduction of grain intake can have adverse effects on their body build and 
going into winter this is not something to mess with. If your horse has a 
"hay belly" make sure he has been dewormed properly. Take a fecal to the vet 
if you are not certain. You can cut back some hay intake but you will want 
to increase this as the weather gets colder- If you are working your horse 
more-he needs more nutrients to burn in his work outs-again the grain intake 
can be altered to accommodate this increase in work. A loss of "butt size"-a 
lack of roundness to their butt is a loss of muscle-not fat. This will take 
the food intake AND strong work outs to rebuild. In older horses this is 
very difficult to do, and in any horse it will only happen over an extended 
period of time. Winter Timing...as we approach the change of the clock, our 
horses may be turned out considerably less than they are in the summer (I 
know mine are). This can lead to boredom and then bad manners, stall 
destruction, etc-you may want to add some longing sessions to your weekly 
routine. A good strong 20 minutes of longing is like a 40 minute ride! When 
you don't have time to go through the routine of tacking up and 
riding-Longe!!!