Hay put up too wet can lead to a number of issues, most notably mold and heat. Moisture keeps otherwise dormant microbes and fungi active, decreasing forage quality and creating heat. Too much heat can actually create a risk of combustion.
How Long Will a Round Bale Last? – Texas Haynet
FIRST QUALITY HAY BY THE JAMISON FAMILY - Blog
Fire is reminder to check your hay
Heat Damaged Forages: Effects on Forage Quality – Team Forage
How to Test Horse Hay Moisture Levels – The Horse
Agriculture, Free Full-Text
A Saudi company took as much water as it wanted during Arizona
Minimizing Hay Storage Loss from Heating or Fires – Riding Magazine
Naturally Better, One Step At a Time – Noble Research Institute