I have horses and have planted things directly into or by accident, currently have a squash of some kind growing in my manure pile of fresh not composted manure. horse is very mild and can be used as a top dressing on trees,roses,asparagus. depending on what the horses where fed and what was used as bedding you may have a bunch of grasses grow up or oats in your garden. best thing to do after your harvest is to cover the area with a black plastic tarp and let it heat up to kill any grass weed seeds.
also check out the back to Eden gardening film for handy no till tips. it saves a lot of back breaking weeding and tilling and you can plant earlier with a better harvest.