Tried a few times long ago, failed each time, fortunately only experimental batches & not whole cut wasted. There just isn't the leeway you get with hay/lage, if it's got the slightest damp it's had it...
With the weather the way it was last year I wrapped all the hay we made, two layers on and from about 90 bales 5 maybe 6 went bad. The trick with it is leaving it out over night for a day or so if weather permits. Though last year it was hay in two days...
Left 100 bales of hay for 5 days last year before getting man to wrap it. Just like the day it went in. Also wrapped 50 bales of straw as a test again just like the day it went in. Obviously very dry last year.
i have a good friend that makes a lot of quality horse haylage , he recons you cant get first cut to dry and it keeps well as there is always some moisture in the stem , second cut or cut mid july on (less sugars ) dead stem will mould unless very dry
Wrapped dry rough hay last year, smelled sweet when baled. Got rats in heap, went mausey. Think grass lacked sugars and moisture to ferment sufficiently and obviously you get condensation in the bale and wet through the layers. Then rats let some air in, all in all a disappointing Winters feed and will not be repeating exercise.
Needs decent grass going in, with some sugar and a bit of moisture.
weve wrapped both hay and straw, hay weve found is best left in field or if possible put in an unused summer shed i.e cured before wrapping for as long as poss and then wrapped before stacking outside, straw has to be very dry and is best if from a crop thats been glyphoed and better still if chopped found a 54321 round stack containing a months supply with a weighted plastic sheet as good and cheaper, the biggest problem is keeping the long tailed feckers out