Factors in feeding:

• Weight, If you don't know the weight of your horse, here are some formulas.
  
• Height
• Age
• Type of work
• Temprament
• Condition
• Energi level
• Feeding problems
• Gain or loose weight

Amount of feed in % of bodyweight

• 2.00-2.25 % Light work, god doer
• 2.25-2.50 % Medium work, average doer
• 2.50-3.00 % Hard work, bad doer

Concentrate in % of feed

• 20-30 % Light work
• 30-40 % Medium work
• 40-50 % Hard work

I am still working on this applet, any comment's are welcome !
Please note that these values are only recommandations and not exact values. Contact your vet. if you have any problems.