I have jsut found out that in our part of the world (north queensland australia) that buying horse poo is not good for the garden at all. Well there's nothing wrong with the horsepoo actually but a bag is half sawdust and this sawdust comes from sawmills where the wood is all treated with poisons such as arsenic, cyanide and something else. So its probably not such a great product for your vegetable garden after all. It might be worth further research if you are going to continue to use it. AT the least find out about the source of your sawdust and if the timber has been treated.