Also consider the NPK values of the various manures... Most all of them are higher in N than in P and K.
N will make them grow like crazy, but without the other two, they won't produce as much fruit, and can be more at risk for viruses and such. So if you do use manure use it wisely. I tilled a bunch of composted manure into the ground prior to planting, and the plants seemed to do really well.
this fall, I'm going to pack the composted manure around the plants really thickly to help protect the roots against freezing (we only have a few in Florida, which is still where my garden is) along with some hay the horses didn't eat (they are messy). The manure I will use is a combination of horse (the main ingredient, and well composted), rabbit (the second main ingredient, and not composted), and chicken (thoroughly composted).
Horse manure contains a lot of still viable seed. Horses don't chew well, and seed from their feed, and hay passes right through. With chicken, it will burn your plants pretty easily. Both of these need composted to help prevent these problems. Whereas the rabbit manure is milder (2,2,2 I think) and has no seeds... For those of you without a bunch of animals to poop in your gardens for you, consider buying composted cow manure from the local big box store. Its something like a dollar for 40lbs of it at Home depot.
Also, do not use manure from any animal that eats meat (dogs, cats, people, and other predators). From what I remember there is the risk of parasites, or bacteria transferring into or onto the plants that humans can ingest, and will make us sick.
Additionally, if you know of people in your area with horses, often and under the right circumstances, they will let you "muck" their stalls for them. Its a chore that must be done daily, and most barns hire help to take care of this particular chore.
If you don't know the owner, you might have a hard time getting them to let you in where their (and their borders) horses are. But its worth asking. They may want to help you the first time, or at least watch to make sure you don't do anything dumb.