Humm you throw it in a well...Oh god that was bad

While manure can be a fairly good nutrient source it is not nearly as good as compost would be, therefore manure should be composted with the right ratio of vegetative waste. "Well rotted" manure and aged manure are about the same thing, manure that is allowed to sit around, exposed to the elements, so much of the nutrients the manure once had is lost.

I have horses and "rot" or compost the manure (it is combined with bedding. Most manure that you obtain will have some bedding mixed in it). I also have free roaming chickens and they turn the manure piles when they are scratching for bugs. It is "done" when it is black and crumbly and looks like lovely loam. The roses love it. My friend used some and she said her plants looked like they were on steroids. Cow manure isn't as "hot" and probably is less likely to have salt in it. I think well-composted cow manure might be your best bet if you are in a dairy farm area and the manure is composted with straw or hay or some other bedding. The only fertilizer I've ever used on my roses is my composted manure and they are very happy.

I also have horses :) and the best manure is when it sits out in the sun for a while (large pasture) and gets dry and almost flakes apart. That's perfect for roses!

If you can't be that picky, just spread out the manure you do find and let it dry in the sun a bit, before you turn it under into the garden. If you're starting a new bed, putting the manure on in the fall and then turning it under in the spring, works really well.