A HOT TOPIC
HOW GOOD HAY GOES BAD
Ron Thaemert and Glenn E. Shewmaker1
INTRODUCTION
The extent of alfalfa storage losses is challenging for the hay producer to measure, unless the total
crop is weighed into and out of storage. These losses are caused by some type of stress related to the
storage. Stress is presented in many forms prior to harvest, but can also occur during storage even
though is may be difficult to recognize and often times impossible to control.
STRESS INDUCERS
Stress can be caused by both visible and invisible influences such as insects, drought, lack of fertilizer
or nutrients, plant maturity, extreme storage moisture at harvest and even accumulation of moisture
during storage. Visible influences (insects, drought and fertility) can often be controlled and
eliminated with proper management practices. The most difficult problems to manage are the
invisible stressors during storage (shrinkage, bale moisture, bale temperature, bacteria, molds, or plant
enzymatic reactions).
SHRINKAGE
Shrinkage of hay is inclusive of both dry matter and moisture losses. Approximately 5 % is dry
matter loss, and the remaining loss is due to desiccation. Typical weight loss is 5-10% in fresh-baled
hay even under shed storage conditions after several months.
BALE MOISTURE, TEMPERATURE, BACTERIA, AND MOLDS
Hay Temperature (°F)
70
110
150
190
230
270
310
____________________________________________________________________________________________________________
plant
respiration
fire danger
fungi and bacteria
heat resistant fungi
Exothermic chemical reactions
(combustion)
Causative agents in the heating of hay
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1
Ron Thaemert, Extension Educator, Blaine County Extension Office, 117 North River, Hailey, Idaho, 83333,
and G.E. Shewmaker, University of Idaho Extension Forage Specialist, Twin Falls R & E Center, PO Box 1827,
Twin Falls, ID 83303-1827. Published in: Proceedings, Idaho Alfalfa and Forage Conference, 24-25 February
2004, Twin Falls, ID, University of Idaho Extension.
The higher the moisture content of fresh-baled hay, the higher the tonnage losses in the stack. Even
though leaf retention is greater in higher-moisture baled hay, the opportunity for mold growth and
other microbial activity is significant. Sugars and starches stored in the hay are significant energy
sources for bacteria, molds, and other microbes to produce CO², water and heat. Thus, causing
increased proportions of acid detergent fiber (ADF) and neutral detergent fiber (NDF) in the hay.
Crude protein content also declines over time, but the concentration may increase due to the loss of
soluble carbohydrates (sugar and starch) to the microbes. As microbial respiration heats the hay, the
usable protein becomes much less because of the browning (Millard) reaction. Browning reactions
occur when microbial activity heats the hay above 100˚ F. Amino acids and sugars combine to
produce insoluble forms of nitrogen. Cows love the taste of the tobacco-like forage and eat it well but
are unable to utilize many of the nutrients.
Enzymatic reactions and mold growth occur up to temperatures of 150˚ F; at temperatures above this
point, most mold and fungal growth cease and chemical oxidative reactions continue to heat the
forage. Higher bale moisture levels increase microbial activity, which heats the bales. Heating will
occur to some extent in all stored forages with moisture levels above 15%. Usually the temperature
will peak from three days to a week after baling, then take 15 to 60 days to decline to non-damaging
levels, dependent on outdoor humidity levels, the density of the bales and the amount of rainfall the
bales absorb. At temperatures above 150˚, producers need to be on the lookout for the possibility of
spontaneous combustion in the stack and be prepared for the dreaded haystack fire. Haystack fires
usually occur within six weeks of baling, but may occur in haystacks several years old. Weathering
begins slowly, but once a wet layer forms, a bale does not shed water well and moisture levels inside
the bale are likely to continue to increase. The wet, moldy area on the top and bottom of the bale
deepens and less drying occurs between snows and rains. Initially, the best strategy to keep “good
hay good” is to bale at the proper windrow moisture level, prevent weathering and limit exposure of
the hay to weathering as much as possible.
Bale moisture content shouldn’t be higher than 18 to 20% in small, rectangular bales, 14 to 16% in
large, round bales, and 12 to 15% in one-ton bales. Moisture levels above these percentage points
may cause damage to the quality of the alfalfa, and extreme caution should be taken to prevent stack
fires.
MANAGING HAYSTACK HEATING
In the event that the hay is stored at too high of moisture content and your haystack is heating the
following steps can be taken to prevent catastrophic losses.
1. Check stack temperature again with another bale moisture and temperature probe.
2. If the hay temperature reaches 130 degrees F, move the hay to allow increased air circulation
and cooling.
3. Separate the hay so that a fire will destroy only a small amount.
4. If the temperature climbs to 150 degrees F or higher, call the fire department and be prepared
to inject water to cool any hot spots before moving the hay.
5. Allocate hay that has been heat damaged to lower producing animals that have lower protein
and energy requirements.
6. Feed the hay as soon as possible.
USING PRESERVATIVES
If drying conditions are poor at baling time, consider using preservatives to prevent heating and fire.
The preservatives may reduce heating, allowing for drying time to be extended and less quality
damage to occur. It is important to remember that preservatives do not reduce moisture levels;
however, preliminary studies by Shewmaker and Thaemert (2000) indicate that, with the addition of
preservatives, bale temperature cycling was moderated compared to the untreated bales.
Note: These figures represent only one observation per treatment and the scales are slightly different.
However, a noticeable difference can be seen in the dramatic temperature fluctuation in the untreated
bale compared to the continuous temperature decline in the preservative-treated bale. There was no
apparent change of forage quality from initial to final as measured by near infrared reflectance
spectroscopy (NIR) predicted acid detergent fiber (ADF) or ADFCP.
THE CURE FOR KEEPING GOOD HAY GOOD
Accurate windrow moisture measurements when baling is the answer. It is important to know where
your hot spots are and prevent from placing them in the middle of the stack. Also, continue
monitoring the temperature of your stacks for six to eight weeks post harvest. If possible, prevent
rain and snow moisture from entering the stack to ensure supreme quality hay.