Horse manure, when well-composted, is a beneficial source of nitrogen which is readily available to plants. Even one horse provides a large amount of manure and if you live near a horse stables, you may have the added benefit of getting manure inexpensively or even free if you move it yourself.
Horse manure is not suitable for vegetable gardening unless it is thoroughly composted. E. coli has been associated with fresh manure. Horse manure also often has wood shavings in it from the horse's bedding. Wood shavings will take nitrogen from the soil in order to decompose. An area for composting and knowledge of composting procedures are necessary for its use.
Utilising horse manure in a vegetable garden is desirable when handled properly. It promotes sustainable growing practices and is useful as an amendment. The knowledge and ability to compost manure thoroughly is necessary to allow sufficient decomposition and to prevent E. coli contamination.