June 2010
Forage Matters

Hay Facts

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.