2 Pack 11lb Refill Bags of Farrier's Formula Double Strength Pelleted Nutritional Supplement for Horses. Double strength formula lasts twice as long as the original Farrier's Formula and provides the same high level of nutrition. Each of the Farrier's Formula Double Strength 11 pound packages delivers twice the number of daily doses compared to 11 pounds of original Farrier's Formula. This equates to a 60 day supply for a 1000 pound horse at the Adult Replenishment Feeding Level or 120 days when feeding at the Adult Maintenance Feeding Level. The nutrients in Farrier's Formula Double Strength are provided at twice the concentration compared to the original Farrier's Formula with the taste that horses love.