Rain damage to cut hay compromises feed quality and palatability. Rainwater washes over the drying forage, leaching away water-soluble nutrients like simple sugars, carbohydrates, and some minerals. This leaching reduces the hay’s overall energy content and digestibility. After a rain event, the goal is to implement rapid actions to minimize further nutrient loss and prevent spoilage before storage.
Immediate Field Strategies for Curing Wet Hay
After a rain event, the most immediate action is to wait until the surface of the windrow is dry before any machinery enters the field. Driving on wet or soft ground risks soil compaction and can severely injure the underlying hay regrowth, leading to long-term field damage. Once the surface moisture has evaporated, the hay must be turned quickly to expose the damp underside to sunlight and air.
Using a tedder to spread the hay out into a wider, thinner layer accelerates drying by increasing exposure to solar radiation and air circulation. If the hay is already partially dry and brittle, physical manipulation must be done carefully to prevent excessive leaf shatter. Since leaves hold the majority of the hay’s protein and nutrients, losing them reduces the final feed value.
The objective is to get the hay to a moisture content suitable for safe storage, typically between 15% and 20% for small square bales, and 15% to 18% for denser large bales. Using an electronic moisture probe is the only reliable way to confirm this level before baling. If the hay is not dried quickly, prolonged moisture reactivates plant respiration, consuming valuable carbohydrates and lowering quality.
Managing Spoilage and Heat Generation
Baling hay with excess moisture creates an ideal environment for aerobic microbial activity, the primary cause of spoilage and heat generation. Fungi and bacteria consume the hay’s remaining sugars, and their metabolic process generates both heat and water vapor. If the internal temperature reaches 130°F, chemical reactions reduce protein digestibility. If it exceeds 150°F, the hay is at risk of spontaneous combustion.
To mitigate this risk when baling hay that is slightly above the target moisture content, producers can apply propionic acid-based preservatives. These organic acid products inhibit mold and fungal growth, effectively stopping the microbial respiration that causes heating. Buffered versions of propionic acid are often preferred because they are less corrosive to baling equipment than the pure acid.
The application rate of the preservative must be precisely calibrated to the hay’s moisture content, requiring consistent monitoring with a moisture probe. For hay between 20% and 25% moisture, an application rate of approximately 0.5% of the wet bale weight is recommended for small bales. Hay exceeding 25% moisture requires a higher application rate, often closer to 1%, but effectiveness drops significantly once moisture surpasses 30%.
Assessing the Usability and Feed Value of Salvaged Hay
After the hay is baled and stored, determine its final usability and economic value. Simple assessments include a visual check for mold, which may appear as white, gray, or black patches. A smell test can reveal spoilage; a musty odor indicates microbial growth, while a sweet, caramel-like scent suggests heat damage from the Maillard reaction.
Even if the hay appears visually sound, rain damage and heating can significantly alter its nutritional profile. Professional feed testing is highly recommended to accurately determine the remaining protein and energy value, such as Total Digestible Nutrients (TDN). Testing also screens for mycotoxins, which are harmful compounds produced by certain mold species.
The safety of the salvaged hay depends heavily on the livestock species being fed. Horses are particularly sensitive to mold spores, which can cause respiratory issues like recurrent airway obstruction, or heaves. Conversely, cattle and other ruminants are generally more tolerant because the microbes in their rumen can detoxify some mycotoxins, though pregnant animals remain at a higher risk for adverse effects.