By Dr. Don Ball
Most livestock
producers rely on hay to feed animals during periods when forage growth is not
available. Both animal performance and the economics of a livestock operation
are greatly affected by the hay program, so now that hay season is in full
swing, it should be a good time to think about some concepts related to hay.
Moisture Content
The general rule regarding
safe moisture-content for baling hay is for small rectangular bales the
moisture content should be 20 percent or less, and for round bales it should be
18 percent or less.
Maturity Affects Quality
Much Alabama hay is
harvested too late. It is psychologically satisfying to get a high yield of
hay, but as yield goes up, forage quality goes down. A "rule of
thumb" is that for every day past the ideal date of harvest, digestibility
declines by one percent. There are undoubtedly many exceptions to this rule,
but it does at least provide food for thought regarding the undesirable effects
of harvesting hay too late.
Rain Damage
Rain can leach nutrients out of
hay; it can prolong respiration losses; it can cause increase
microbial-activity that consumes nutrients; and, in the case of forage legumes,
it can increase leaf shatter. Nonetheless, there is probably more overall
economic loss associated with hay being cut too late than from rain damage. A
hay producer obviously cannot ignore the weather, but it is worthwhile to keep
in mind the threat of rain is just that -— a threat which may or may not
happen. Delaying of hay harvest beyond the optimum harvest stage is certain to result in lower forage quality.
The extent of rain
damage to hay is correlated with the amount of rainfall, with legume hays
generally being damaged more by rain than grass hays. Also, rain coming soon
after hay has been cut is less damaging than the same amount of rain which
comes just before the hay would have otherwise been ready to bale.
Weathering
The more the hay on the outside of
a bale becomes weathered, the more it will hold water, which favors the growth
of microorganisms involved in causing hay to spoil. Thus, the rate of spoilage
tends to increase over time. Most weathering of round bales stored outside
occurs in a layer usually six to eight-inches deep around the rounded edges of
the bale. Other things being equal, there is a lower percentage of spoilage
with large-diameter round bales as compared to smaller-diameter round bales.
Heating
When hay is baled at too high a
moisture-content, heating will occur due to the activity of microorganisms.
This heating process lowers hay quality and, in hay having particularly high
moisture content, can create a fire hazard. The temperature of hay can be
monitored by driving a hollow pipe into hay bales and inserting a thermometer
into the pipe. A temperature of less than 120 degrees Fahrenheit is normal;
from 120 to 140 is getting into the danger zone; hay having a temperature of
160 or higher is likely to catch fire.
Hay known to have been
baled at an excessively-high moisture-content, or known to be heating
excessively, should be placed in a location where minimal damage would result
if a fire occurred. Such hay should certainly not be placed in a barn and
freshly-baled hay should never be placed against dry hay. Heating usually
reaches its peak after about a week. Thus, after about two weeks a spontaneous
fire is unlikely.
Toxicity From Hay
Almost every year some
Alabama livestock producers have animals die from consuming hay with high
nitrate content. The usual situation where nitrate levels become dangerously
high is when high levels of nitrogen fertilizer are applied (60 pounds or more
of actual nitrogen per acre) and low rainfall results in poor forage growth.
Nitrate poisoning is possible with many forage species, but it occurs most
frequently from feeding summer annual grasses (including sudangrass, sorghum,
sorghum-sudangrass hybrids and especially pearl millet) and from certain weeds
including smartweed, goldenrod, ragweed and pigweed.
Hay suspected of
containing high levels of nitrates should be tested to determine whether it is
toxic. Getting a representative sample of hay for testing is important because
some plant parts (especially stems) may contain higher levels of nitrates than others.
Nitrate testing is provided for a small fee by laboratory facilities that
routinely test hay, including the Auburn University Soil Testing Laboratory.
Each year questions
also arise regarding the possibility of poisoning from prussic acid in hay.
Prussic acid, also referred to as hydrocyanic acid, can build to toxic levels
in sorghum, sorhum-sudan hybrids, sudangrass and johnsongrass in pasture
situations, usually immediately after a killing frost. However, prussic acid is
an unstable compound and is not a
problem in dry hay.
Don Ball is an Extension Forage Crop Agronomist with
Auburn University.