If you think your horse might be overweight – it is. How is it best to evaluate the body condition of a horse? Use the Henneke Body Condition Evaluation. The following document is a copy of the chart utilized for condition scoring of a horse:
The following link is an excellent article from the publication: Equus, February 2009, that shows horses with various body conditions.
I find the best way to evaluate weight loss in a horse is to take several digital images (back view, front view and both side views), then periodically repeat the same series of views and compare. It is difficult to evaluate changes in weight when you observe a horse on a daily basis. Sometimes weight tapes can be misleading – a horse that is being exercised may exchange fat for an increase in muscle mass.