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.
Baling wet hay could cause fire
Global principles in local traditional knowledge: A review of
Ch 3. Cultural Weed Management - SARE
Monitoring hay to prevent barn fires
The Management and Use of Bahiagrass
A Skeptical Look at Mob Grazing
Texas Hay Season Looks Bleak
Hay production is costly, time consuming
Preventing Hay Fires: Tips for Decreasing Hay Moisture Levels
Baleage: Frequently Asked Questions
Effect Of Heating On Feed Value Of Hay