Fresh Horse Manure for Fertilizer

I'm in Santa Cruz, CA where it only rains six months of the year. My diverse orchards are on drip systems, and I do fertigate, but last year I started dumping fresh horse manure on my trees also. I'm on top of a ridge, and there is no vehicular access to the trees, so I hand carry 5 gallon buckets of my neighbor's fresh horse dumplings--diverted from the dump in a recycling cart on wheels--down to deposit within the dripline of each tree. This is getting difficult as I am approaching 70. On the downside of each tree at the dripline I installed a chickenwire foot-high fence to reduce the effects of gravity and chicken scratching. Since I've been doing this for a year, it seems the trees can handle the raw manure, which was an original concern. Being a true permie, I wanted to avoid the intermediate step of composting if possible--too much work. Then, I read recently about nutrient volatility and I'm afraid that the fresh manure nutrients I dump in the summer just dry up and float away. If this is true, I suppose I should only dump this free gold in the winter, when rain will send the nutrients down instead of up. Any suggestions on this?

Perhaps you could cover the horse manure with a loose pile of soil, or leaves - still allowing rains to soak through.
Whatever 'loss' you have would be lost into the soil/leaves rather than the atmosphere.

I can only speak for my climate, and the winters aren't that cold compared to many Northern hemisphere places.
There's major problems here with adding manure over the winter, as the bacteria are very slow and can't process the nutrients, which tend to end up in the water.
Like John says, I'd dump lots of mulch on top.
I'd go for a high-carbon mulch like chipped trees, as it should help 'hold' the nitrogen, as well as being a fungal tree banquet

one good reason to compost the manure first is that compost is so much more nutrient dense than the origional manure. so especially when you are carrying it uphill by the bucket, you get many times the benefit for your labor in carrying.

It sounds to me like you are carrying the manure down the hill. Why not just pile the manure at the top of the hill and leave it to compost. Horse manure is close enough to the proper C:N ratio that it doesn't have to have extra carbon. Don't turn the compost as that promotes more fungal growth and leave the piles for a year. Any runoff will run down hill into the orchard. Carry only finished compost down the hill to save labor.