Backyard Gardener: Value of rained-on hay

Hello Mid-Ohio Valley farmers and gardeners! The summer continues to be hot and humid up as heat indexes rise into the danger zones this weekend. The warm temperatures and ample rain are producing great crops for beans, tomatoes and other vegetable. Although many farmers planted late this year corn and soybean crops are improving. This year is looking similar to last year as a tough time to harvest hay in a timely fashion.

Heavy and prolonged rainy periods have delayed hay cutting for many farmers. Producers have also have cut and watched hay get rained on. What is the value of this damaged crop? Rain occurring while cut hay is laying in the field causes both yield and quality losses that reduce the value of the crop as a livestock feed and a marketable product.

Most farmers have experienced hay getting rained on. First of all, there are many variable to consider. Both rain intensity and duration impacts the amount of damage caused to cut forages. Rain that occurs soon after cutting is less damaging than if rain occurs just before the cut forage is nearly dry or worse is raked into windrows and ready for baling. Recently cut forage is not going to soak in as much moisture from the rain, resulting in less nutrient loss and delayed baling.

Rain that soaks into nearly dry forage will cause leaf shatter and nutrient leaching. The amount of yield loss is highly variable and difficult to predict but University research has resulted in losses ranging from 5 to almost 50%.

Given the same amount of total rainfall, a low intensity rain will result in more leaching of soluble compounds than a high intensity rain. Also, as forage moisture content declines, it is more prone to dry matter loss from rain. In University of Wisconsin rainfall studies, the maximum loss in dry matter (54%) was where 2.5 inches of rain fell on hay that was nearly dry(this was alfalfa hay and there is more leaf loss with legumes than grass).

Rain has a negative impact on hay by reducing the energy content and increasing the fiber due to leaching and prolonged plant respiration. Leaching is the movement of highly water-soluble cell contents out of a plant and is most often encouraged by hay getting rained on. Unfortunately, most of these leached components are highly digestible by the animal, and include soluble carbohydrates, soluble nitrogen, minerals, vitamins and lipids. Almost half of dry matter leached by rain is soluble carbohydrate. As a result, energy values decrease with leaching of nutrients, and fiber content of the forage increases.

Respiration is the breakdown of soluble carbohydrates by plant enzymes. Each time cut forages are wetted by rain, respiration is prolonged or restarts and this also causes additional losses of sugars from the plants. Leaf loss is a particularly significant problem in legume hays as compared to grasses. Rainfall may mean additional handling of the swaths prior to baling to speed up drying resulting in more leaf loss, particularly from alfalfa. Every time hay is raked, there may be a 5% loss in tonnage due to leaf loss. Rain can also encourage more microbial activity resulting in metabolizing of soluble carbohydrates, thereby reducing forage energy content.

Hay baled too wet also is susceptible to heat damage, also called enzymatic browning. The hay will smell good and livestock will readily eat it but nutritional values may be low. These heat-damaged protein compounds are poorly-digested but often smell sweet like caramel. If sampling forages, special laboratory tests are available that can measure heat-damaged protein and then adjust crude protein values.

Mold can be an issue and is common in rained-on hay. Often the hay was baled too wet, either to avoid further rain damage or just to remove it from the field to reduce its impact on regrowth. Mold can render hay less palatable, which can result in lower livestock intake or outright refusal to eat the hay. Feeding moldy hay also has some risks involved.

Ruminant animals such as cattle are generally less sensitive to mold since many mycotoxins are broken down in the rumen. However, certain molds can cause mycotic abortions or aspergillosis. Horses are much more sensitive to mold and spores often contribute to respiratory and digestive problems like colic or heaves.

Also, keep in mind pregnant and young animals are at a higher risk and livestock in poor condition are more likely to be affected. Mold can also cause a condition called farmer’s lung, where the fungus actually grows in lung tissue.

Determining the risk of mycotoxin poisoning from moldy hay can be very difficult. Laboratory analyses for molds and mycotoxins are available but are relatively expensive. When sampling for potential toxins gather samples from what is thought to be the bales and areas within bales that are expected to be the most dangerous. Then feeding strategies can be developed to protect animals from what might be their worst-case scenario in terms of toxicity. If feeding moldy hay, consider spreading the hay out on the ground so that animals avoid the moldy portions while consuming good hay.

Rained-on hay does not necessarily mean ruined hay. The only true way to determine the real nutritional value of your hay is to take a good composite sample have it analyzed at a forage testing lab. Contact me at the Wood County WVU Extension Office 304-424-1960 or e-mail me at with questions. Good Luck and Happy Gardening!