Horse muck/. Cover or not

Just filled two wooden compost bins with horse muck ready to apply to the beds next autumn as it's far too fresh now.  Should I cover them with plastic  or will they be ok as they are?

Although composting requires some moisture to help it along, it's hard to control the amount if the pile is left open to the elements, so best to cover it, watering if necessary.

(Fast composting also requires air, but your bins will allow for that if they are of slatted construction.)

JayG got it spot on!

Thanks all