The weather challenges from 2015 continue to present themselves. As I write this, available forage is on the wane due to dry conditions. For many producers, it’s time to feed hay. And much of that hay might be of low quality because, in the early summer monsoons, it was rained on before it got baled.
There are no robust guidelines that can accurately estimate the amount of damage or the actual feeding value. The factors influencing rain damage are just too variable. They include the amount of rain that fell on the hay and how long it rained. How dry the hay was before the rain has an effect, as does the drying conditions after the rain. How the hay got raked between the rain and baling, moisture of hay when baled and quality of hay when cut are also factors. Mold is common in rained-on hay. Often the hay was baled too wet, either to avoid further rain damage or to remove it from the field to reduce its impact on regrowth. But even when the bales are ready and waiting, feeding moldy hay to livestock is a tough decision.
All hay contains some mold, but when mold becomes easily noticeable, feeding management becomes more important.
Usually, mold makes hay less palatable, which can result in lower intake or even in animals refusing to eat the hay. Other problems from mold can occur due to mycotoxins produced by certain mold fungi. This also is part of the decision process, since not all molds produce mycotoxins. When they do produce mycotoxins, it’s hard to predict how much they will produce. The good news is, mycotoxins rarely are present in hay unless it has mature seeds.
Laboratory analyses for molds and mycotoxins are available, but are relatively expensive. Often, each mycotoxin must be measured individually. That increases the cost, and if you aren’t testing for the right mycotoxin, can give you an incomplete picture. Moreover, the test is based on the sample hay sample you send in, which may or may not be representative of the larger hay supply. Mycotoxin concentration usually is highly variable.
Direct negative effects of moldy hay are difficult to document. Horses may be the most sensitive to mold among common livestock. For example, mold spores often contribute to respiratory and digestive problems like colic or heaves in horses.
The best course of action is to minimize feeding moldy hay to more sensitive animals, like horses or pregnant cows. This may require a keen eye or sensitive nose when selecting hay to feed each day.
Mixing moldy hay with other feedstuffs can dilute mold problems, but be careful that you don’t make your animals sick by tricking them into eating bad hay that they normally would refuse.
Hay baled too wet is susceptible to heat damage, also called enzymatic browning. It is caused by heat produced by microorganisms in the hay as they use plant sugars and oxygen. If enough heat is produced to raise hay temperature above 125 degrees, chemical reactions occur that combine amino acids from protein with sugar to produce compounds similar to lignin.
These heat-damaged protein compounds are poorly digested but often smell sweet like caramel. You may see hay turn a tobacco-brown color. This damage sometimes produces flavors that cattle find exceptionally palatable.
Although livestock may favorably consume heat-damaged hay, the protein value they get from it can be unexpectedly low. Standard forage tests can predict energy available from heat-damaged hay, but the standard crude protein test cannot distinguish between usable crude protein and heat-damaged protein. Thus, standard tests may significantly overestimate the usable protein in the forage.
The lab test used to measure heat-damaged protein, which can then be adjusted to account for the digestibility/availability of the feed protein, is the acid detergent insoluble nitrogen (ADIN) test. It is also known as acid detergent fiber crude protein (ADF-CP) or insoluble crude protein (ICP). When heat damage is suspected, ask your lab to conduct this test and adjust crude protein accordingly.
Rain damages hay in several ways. It leaches soluble carbohydrates, proteins and minerals out of the hay. Leaves are lost. Extended drying time reduces carbohydrates due to plant respiration and microbial activity.
Three primary factors are involved in dry matter losses—leaching, respiration and leaf loss. Leaching is the movement of cell solubles out of the plant. Components of the plant that are very water soluble are leached out of the forage and lost when rained on. Basically, if a nutrient is highly digestible, it is also prone to leaching losses. About half of the dry matter leached by rain is soluble carbohydrates.
Most often, fiber concentration increases and crude protein concentration remains about the same after hay has been rained on. Digestibility and energy usually decline. The increase in fiber concentration is due to soluble carbohydrates and other components leaching from the hay—fiber isn’t actually increasing.
The digestibility of rain-damaged hay will be reduced. Many factors contribute to this: leaf loss, soluble carbohydrate leaching, the increased levels of fiber and ash by concentration. Forage digestibility may be reduced by just a little or up to a third.
The amount of change in nutrient concentration is highly unpredictable. If you are counting on hay that has been rained on or put up wet, a laboratory analysis for nutrient content will help you adjust the supplements you need to keep your livestock in condition