How Does Rain Impact Hay Quality?

The classic summer afternoon rain shower is both a friend and foe for hay producers in the Southeast.  While most farmers certainly won’t turn down a year with ample rain, the frequency of rainfall can pose a challenge to putting up high-quality hay for the winter months.

Rain can cause the following to occur when hay is being cured in the field prior to baling:

  • Leaching – Hay that is closer to baling, or more dry, is more susceptible to leaching losses than fresh cut forage. Nutrient leaching causes dry matter loss, increased fiber and decreased energy value of forage.
  • Respiration – Losses to respiration occur when moisture levels exceed 30%. When forage is re-wetted by rain, this keeps the forage moisture level high enough for respiration to continue or be prolonged, which results in carbohydrate losses in hay.
  • Leaf loss is generally more significant in legume than grass hay, and amount of loss is often quite variable. Additional handling of windrows to encourage drying post-rainfall contributes to leaf loss.

Rain damage increases with the amount, duration of a rainfall event, and timing relative to when hay was harvested.  If rain occurs shortly after cutting, this is usually less damaging than hay that has already had significant drying time in the field. A research trial at the University of Arkansas reported that a short delay in harvest of perennial warm-season grasses had a more negative influence on hay quality than a single rainfall event ranging from 0.5 to 3 inches. Repeat instances of rain cause more damage than a single rainfall event. This is generally where more significant quality and dry matter losses occur, especially for hay that is still above 30% moisture that continues to respire.

Even if hay has been rained on multiple times, it is important to get the forage out of the field to minimize the impact of excessive thatch on forage regrowth for the next hay harvest. Higher moisture bales may undergo heating, and also provide a favorable environment for mold growth. Collect a forage sample from rain-damaged hay to send in for nutrient analysis to determine overall feed value and suitability. Rain-damaged, low-quality hay should be used for cows in the herd with the lowest nutrient requirement.

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