Barastoc Rebalance Horse Block A protein and mineral supplement for horses. When they are being spelled, horses depend completely on pasture for nourishment. However, pasture is often not sufficient to provide horses with everything they need - particularly in terms of proteins and minerals. Fortunately you don't need to take risks with your horses when they're in the paddock. Barastoc Rebalance Horse Block is the ideal solution for times when pastures are not of optimum quality.