Likewise, remove any uneaten grain or pellet mixture, clean the feed tub and begin afresh. These small actions will make a BIG difference in the amount of feed you get inside your horse. It pays to question why your horse isn't eating well. If he's sick, the answer is obvious. If he's just mysteriously losing weight with no apparent cause, it pays to study the situation.
Horses are very sensitive to changes in their surroundings and are schedule oriented.
The better you know your horse's personality and temperament, the more likely you'll be to spot a small but significant change in his routine that could be upsetting him and putting him off his feed. Of course you'll want to consult your Veterinarian to rule out any medical cause for the lack of appetite. I'm afraid you haven't told me much. Different types of hay and, indeed, even different bales of the same type of hay can vary greatly in the weight of a single flake. Likewise, a one-pound coffee can rarely holds exactly a pound of grain or pellets.