How Rain Affects the Quality of Hay

This year’s haying season has had it’s fair share of difficulties. Cool temperatures and frequent rains have made making good quality hay a difficult business. Rained on hay has reduced yield and quality. Not only are there issues with storing and feeding lower quality hay, it’s also not as marketable in today’s market conditions; where many buyers may not have the money to pay for it, or are not willing to take the risk of continuing to feed cattle that may not have a market. More often than not, it’s years like this that we see only the “cream of the crop” (best quality feed) being bought, and the medium to lower quality being feed at home.

Rained on hay accrues losses via the following ways:

  • Leaching of soluble carbohydrates and certain minerals (protein often not significantly affected)
  • Mild/long-term rainfall events will remove more soluble nutrients than short-term/ intensive rainfall events. As much as 50% of the dry matter removed might be soluble carbohydrates. These carbohydrates are what feed the microbes in charge of ensiling, thus loosing them can reduce the option to ensile the crop. Additives can be used to supplement lost carbohydrates, but this adds cost.
  • Increased and prolonged plant respiration
  • The plant continues to convert collected carbohydrates to CO2 gas until it reaches 30% moisture. Re-wetting the hay beyond above 30% moisture will essentially restart the respiration process
  • Leaf shattering and loss Continued handling (e.g. raking) to dry the swath, along with frequent wet – drying cycles increase the leaf drop.
  • Microbial activity. Wet hay will support continued microbial breakdown of plant structure and nutrients, and promote the development of molds.
  • Color bleaching. Continued exposure to the sun and elements will result in the loss of green color, thus reducing marketability.

How Baling Wet Hay Affects Storage Management

Due to the unpredictable weather, many producers ended up baling their hay a little wet.

When storing these bales, it’s important to note that bales automatically increase in temperature after baling due to microbial activity and plant respiration inside the bale; generally up to about 540 C. Bales also keep the heat of the day inside if baled during a hot day.

Therefore, if you plan on storing hay inside a building (e.g. hay for export), it is at risk of spontaneously combusting when baled at 18% moisture or greater.

To counter the risk of heating and mold development, some producers have added natural enzyme-based additives in hays baled above 20% moisture; others have stuck with using more traditional acid-based additives. If you have assumed some risk in baling this years’ hay a little wetter than normal you need to MONITOR YOUR STACK while aware of the details below. If you’ve baled wet hay that is at risk to heating, leave the hay unstacked for the first 3 weeks after baling, allowing the heat to escape.

If you do stack the hay, use a temperature probe to measure heat. Probe the stack in several places, making sure to reach the middle (therefore may need 2-3 foot long thermometer). Buy one that can read up to at least 950 C.

The cheaper option is to build your own from ½”- ¾” steel pipe. Pinch one end and drill 3 to 4 small holes in the side of the pinched end to allow air flow. Then weld a T-shaped handle on the other end. Then simply slide a glass thermometer on a string down the tube which is stuck in the stack. Check your stack as frequent as possible; once a day is a nice place to start. If temperatures are rising, consider pulling the stack apart to cool off. Be sure to check the most tightly packed area in the bale as this is where the temperatures will first begin to rise. For example, check within 6-12” from the center of a round bale. Use the temperature ranges below to determine the risk of losing the quality of your bales to heating.

  • Up to 490 C: Caused as fungi and bacteria carry out normal respiration. The process is referred to as normal sweating during hay curing. This temperature rise occurs when hay is baled at 15-20% moisture. These temperatures generally do not cause serious concerns in forage quality loss. However, mold may develop at this temperature range.
  • 43-650 C: Caused by fungi able to grow at this temperature range. Chemical re-actions during heating will denature some protein and cause some fiber to be less digestible.
  • 57-710 C: Caused by fungi respiration. At 650 C, check temperature every day. At temperatures above 710 C, chemical reactions dominate the heating process. If the temperature continues to rise, check it every four hours. At this stage, the situation may become dangerous.
  • 790 C: Continue to check the temperature every few hours and notify your local fire department. Do not attempt to move the hay without fire department assistance.
  • 900 C or more: Spontaneous combustion is possible. Ask your fire department to assist you.

Source: North Dakota State University; South Dakota State University; Iowa State University Extension.