One AC is weight dependent. Average size horse, 950-1100 lbs, one teaspoon twice daily ( AM & PM). Horses over 1100 lbs add 1/2 teaspoon for every 100 lbs over maximum weight.
Horses 600-900 lbs 1 1/2 teaspoons daily (3/4 AM - 3/4 PM). 300-600 lbs one teaspoon daily. Miniature horses respond well to 1/2 teaspoonful daily.