Determining the Value of Rained-On Hay

George eating hay in his paddockRain occurring while cut hay is laying in the field causes both yield and quality losses that reduce the value of the crop as an animal feed and a marketable commodity.

Weather-induced losses are caused by:

  1. Prolonged plant respiration reducing soluble carbohydrates and overall energy content
  2. Leaching of soluble carbohydrates, protein, and certain minerals from the hay
  3. Leaf shattering and loss, removing the highly digestible and high protein portion of the forage
  4. Microbial activity metabolizing soluble carbohydrates and reducing energy content
  5. Color bleaching

How much does rainfall reduce dry matter yield?

Several researchers have studied the effects of rainfall on cut alfalfa. Wisconsin researchers measured dry matter losses of 22% when alfalfa was exposed to 1 inch of rain after 1 day of drying (curing). Similar hay dried without rain damage lost only 6.3% of the initial yield. Losses appear to be greatest after partial drying of the forage has occurred. In this same study, alfalfa exposed to 1.6 inches of rain over several days suffered a 44% loss in dry matter. Michigan researchers conducted several different studies to examine the effects of rainfall on field cured alfalfa. The first study reported maximum dry matter losses of 34%. In a second study, rainfall intensity was kept constant at about 0.7 inches but spread over periods of 1 to 7 hours. Dry matter losses ranged from 4 to 13%, with highest losses occurring when the rain was spread over a longer duration. Overall, dry matter losses were much lower in these experiments even though rainfall amounts were about 2 inches.

Other species have been studies as well. Yields losses of birdsfoot trefoil appear to be less than alfalfa, while red clover shows even less dry matter loss due to rain, and grasses suffer the least amount of dry matter losses. Dry matter losses are most crucial to the person responsible for baling the hay. Dry matter losses usually represent a significant decrease in income since less hay is available for baling, feeding, and selling.

How does rainfall reduce dry matter yield?

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 rain occurs. Unfortunately, most of these compounds are those highly digested by the animal. They include such components as readily available carbohydrates and soluble nitrogen, minerals, and lipids. About one-half of the dry matter leached by rain is soluble carbohydrates.

Unlike other livestock, losses of soluble carbohydrate can be beneficial for some horses. Laminitis is a painful and debilitating disease of the horse hoof. Laminitis typically occurs during periods of increased or rapid intake of water soluble and nonstructural carbohydrates. In order to manage lamintic horses and reduced amounts of carbohydrates in harvested forage, horse owners have resorted to soaking hay. A number of research trials have confirmed removal of carbohydrates from hay by soaking in either 30 minutes of warm or 60 minutes in cold tap water. Soaking hay is a cumbersome, messy, and time consuming process. Purchasing rained-on hay with naturally low levels of carbohydrates is a possible alternative.

Respiration (breakdown of soluble carbohydrates by plant enzymes) occurs at nearly 2% dry matter per hour in fresh forage, and declines almost in proportion to the decrease in moisture content until the plant reaches approximately 60% moisture. Every time the forage is wetted by rain, respiration is either prolonged or begins again in cases where the cured forage was below 60% moisture. In either case, additional dry matter is lost.

There is some disagreement in the research literature regarding the amount of leaf loss that occurs in cut alfalfa as a direct result of rainfall. In Wisconsin studies, leaf loss ranged from 8 to greater than 20% as a percent of the initial forage dry matter when rainfall amounts were from 1 to 2.5 inches. In Michigan studies, direct leaf loss was much lower (0.5 to 4.2%). Perhaps the issue of leaf loss from rainfall is a mute point. Experience and common sense tell us that rain damaged alfalfa is more predisposed to leaf shatter after it dries, and rainfall often means additional raking and more lost leaves.

How does rainfall intensity and forage moisture affect losses?

Research is conclusive on these two points. 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 Wisconsin rainfall studies, the maximum loss in dry matter (54%) was a treatment where 2.5 inches of rain fell on hay that was nearly dried.

How does rainfall affect forage quality?

Perhaps nothing is more frustrating than to see excellent quality alfalfa turn into unsuitable feed with each passing rain and subsequent raking. Most rainfall studies are in agreement that wetting of field dried alfalfa has little impact on protein concentration. For rained-on hay, it is common to see relatively high protein values in comparison to fiber concentrations, unless significant leaf loss occurs. With the leaching of soluble carbohydrates, structural fibers (acid and neutral detergent fibers) comprise a greater percent of the forage dry matter. Depending on numerous factors, the digestibility of rained-on hay may decline from 6 to 40%. Changes in fiber components are thought to occur by indirect mechanisms, where the respiratory activity of microorganisms has a concentrating effect on fiber components by oxidizing carbohydrate components; additional fiber is not made during the wetting process.

Conclusion

Rained on hay can be a suitable forage, but quality depends on several factors. Forage quality tends to be retained if rain occurs soon after cutting when the forage has had minimal time to dry; the rainfall was a single event compared to a multiple day or drawn-out event; rainfall intensity was higher versus a longer, lower intensity event; and the forage has not been re-wetter numerous times. Rained on hay is actually beneficial for horses prone to laminitis and other metabolic disorders because of its reduced carbohydrate content. Analyzing forage for nutrient content is recommended, but can be especially useful when determining the quality of rained on hay.

This article is reprinted with permission from Dan Undersander, University of Wisconsin and Krishona Martinson, University of Minnesota. This and other horse nutrition articles can be found at http://www.extension.umn.edu/agriculture/horse/nutrition/.

When Should I Feed a Complete Horse Feed?

A complete feed is a fortified grain/forage mix that is formulated with high quality fiber sources to raise the total percent fiber in the feed, so that reduced hay feeding can be done safely. Some fiber sources in complete feeds include alfalfa, beet pulp, and soy hulls. These are all good digestible fiber ingredients for horses.

Here are some of the many reasons why you might decide to feed a complete feed.  

  • You have a horse with poor teeth or no teeth that can no longer chew and swallow hay. This can be a young or old horse.
  • Good quality hay is hard to find, obtain, or pay for. This situation will most likely occur in:
    • Drought situations when plants aren’t growing or they are very mature when they get tall enough to cut. When a plant gets too mature it has high levels of lignin that can’t be digested by the horse leading to digestive upsets or increased risk of colic. Plants also lose nutrient content the more mature they get.
    • Extremely wet conditions because it may be more mature by the time a farmer gets good weather to cut it and flooding can also bring debris onto fields that can be harmful to your horse.
    • Situatinos where hay gets more expensive as fertilizer and fuel costs rise.
  • There is a lot of hay wasted from handling, transporting, ect. More hay is wasted when horses are fed round bales. When hay is expensive and there is a lot of waste, complete feeds may be more cost effective.
  • Hay is hard to handle and round bales/large square bales require a tractor for handling and other equipment such as a flatbed trailer. Equipment requires fuel, tires, maintenance, ect. The cost of handling hay should be brought into consideration when cost is a major factor in feeding.

Long stem forage is an important part of the horses diet and a good source of forage should comprise of at least 50% of the horses daily intake when possible. However, when any of the above conditions exist it may be necessary to feed a complete feed only or reduce the amount of hay being fed. A horse that can no longer chew hay will need to get all of his daily requirements from a complete feed that is easy to eat such as a senior complete feed with softer pellets that can also be fed as a wet mash. If hay shortage, hay cost, or drought is the reason you feed a complete feed you may want to continue feeding some hay in the diet for long stem forage if possible.

It is important to read and follow the feeding recommendations when buying a complete feed, and they should list the recommended feeding amount both with and without hay on the tag. As you decrease the amount of hay, you will need to increase the amount of complete feed. Here are two examples of complete feeds and how much to feed a 1,000 lb maintenance type horse with no hay and with hay/pasture.

  • A senior horse feed – generally a highly digestible and highly palatable product that can be fed as a complete feed, and is designed for older horses. 
    • A 1,000 lb maintenance type horse would receive 12 – 14 lbs of a senior feed, if no additional hay is fed.
    • The same horse, if it was being fed hay, would receive 5 – 7.5 lbs of the senior feed.
  • A traditional complete horse feed – known as “hay replacers” or “hay stretchers” – are a complete feed that combines high quality roughage and grains in a pelleted form. It can be fed as a complete feed or with forage. 
    • If no hay is fed, a maintenance type horse would receive 1.5 lbs per 100 lb body weight. A 1,000 lb horse is recommended to get 1,000/100 = 10 x 1.5 lbs = 15 lbs of a complete feed.
      When feeding along with hay or pasture, a typical recommended amount to feed a maintenance type horse 0.5 lb per 100 lb body weight or 5 lbs.

Whether you chose to feed a complete feed with hay or without, it is important to feed the recommended amount and make adjustments as needed depending on if your horse is an easy or hard keeper. It is also important to provide free choice salt and clean, fresh water at all times. Complete feeds should be split into two or more feedings. Horses should be switched slowly from one feed to another and also when eliminating hay from the diet. When reducing the amount of hay fed, it is recommended to reduce hay over 1-2 weeks.