Christine and for all “no dig” gardeners, wrestling with how best to use horse manure in their gardens …
The following YouTube video might be of interest https://www.youtube.com/watch?v=K9_yWQATxNI
You will see there an excellent suggestion for aerating your pile by using PVC pipes, at the bottom of the pile, suitably “holed”. I suggest 75, 100mm diameter pipe (3, 4 ins). This will act as a passive ventilator, and provide excellent aeration for your pile of horse manure (or horse manure, plus shavings etc.), especially in the bottom 1/3 of the pile, where aeration can be a problem, because of compaction or excess moisture.
One of the lessons that I have learnt – through years of “wrestling” with horse manure, and how best to incorporate it into your garden – is the need to plan ahead. In other words, today’s fresh horse manure, will be useful in 3 to 6 months at a minimum.
Only my experience. Hope that this helps.