I'm with goodlife on this, horse manure isn't anythng like as "strong" as pig or cow so it can be used straight away as a mulch, especially at this time of year. Woodshavings is good in one way, a lot of the straw bedding seems to be contaminated with weedkiller and can give some plants (especially tomatoes, beans and potatoes) a hard time before it fades (takes a couple or three years if you get it, it's a pest)... I'd be spreading it straight on there as a mulch for things lie rhubarb, asparagus once it dies down, raspberries etc... once we've had some rain then the winter brassicas would be a good place to put it.... you could also make a winter salad warmbed if you have a cold-frame spare and fancy digging a hole.... go down about a foot, pack it with your fresh horse poo, put a couple of inches of soil on it and cover with a cold frame, sow it with winter-hardy lettuces, spring onions and pretty much anything that's green and leafy, even things like fennel... treat it as a source of salad leaves through the winter, the manure will keep the temperature up a few degrees the whole way through.... you need to keep an eye on watering as the frame will keep it drier than normal....