How Preservatives Affect Hay Moisture

How Preservatives Affect Hay Moisture

May 16, 2008

The moisture content of hay when it is baled influences yield, quality, and storability.

When hay is baled too dry, leaves fall to the ground, reducing both quality and yield. Unfortunately, hay baled too wet can get moldy, overheat, or even catch fire. There is a narrow moisture range that results in good hay that keeps well.

Hay can be baled a bit wetter if a preservative like propionic acid is applied as it's baled. To get good results from preservatives, though, it helps to know how it works and what it can and can not do.

Baled hay naturally contains millions of bacteria and mold fungi. As they consume hay nutrients, these microbes produce heat. The duration and intensity of this heat determines the amount of damage to the hay.This heat also forces moisture out of the bale, something called "going through a sweat." Usually, hay gets dry enough that the microbes die or go dormant, but when too much moisture is present, heating becomes excessive, mold develops, or both. However, preservatives kill many of the microbes so lthere's less heat.

This gives hay time to dry out naturally, without the "sweat." But as it dries, the preservative also vaporizes and disappears. If bales are not allowed to dry properly or are stacked tightly and stored soon after baling, the remaining microbes eventually will produce the heat and mold the preservative was to combat. Also, if rain, high humidity, or other sources moisten the hay later, microbial activity can redevelop since the protection from preservatives lasts only a short time.

Preservatives can help make good hay at higher moisture levels but correct management is needed to keep that hay in good shape.

Bruce Anderson

Extension Forage Specialist

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