Lucky you! Lots of people don't realize the manure does have to be
"aged".

Yes, I am lucky. My husband brings me a fresh pile every year so the
previous years doesn't always get used up.

As to your question: what is in the soilless mix?

Pro Mix is a general growing medium. I don't know what is in it. I
use it to start my seeds but I have found that when I transplant into
my outside planters that they do not do so well even though I
fertilize with Miracle Grow. This year I thought perhaps if I mixed
with manure I would have better looking plants.

Lori