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Articles of Interest - August 2001


In agriculture, dried grasses and other foliage used as animal hay. Usually the material is cut in the field while still green and then either dried in the field or mechanically dried by forced hot air. Typical hay crops are timothy, alfalfa, and clover. The protein content of grasses and legumes decreases, and the fiber and lignified tissue increases as growing plants advance in maturity. For good hay, the crop must thus be cut at the proper stage, handled so as to retain the leaves, and cured to prevent spoilage or discoloration. Hay is usually dried in small piles or stacks in the field, but a rainy climate may dictate forced-air curing in the barn. Properly cured hay with 20 percent or less moisture may be stored for months without danger of spoilage.

Until the middle of the 19th century, hay was cut by hand with sickles and scythes. In the 1860s early cutting devices were developed that resembled those on reapers and binders; from these came the modern array of fully mechanical mowers, crushers, windrowers, field choppers, balers, and machines for pelletizing or wafering in the field.

Balancing Loss and Hay Quality

The most important factors affecting the quality of hay are 1) moisture content at baling and time of storage, 2) stage of maturity at baling, 3) storage conditions, and 4) the forage species, of course. This guide has information on the first three factors as well as on hay preservatives. It does not deal with forage species.

Some forages, such as alfalfa, orchardgrass, red clover and so forth, have higher feeding values than some other forages. If you have questions on forage species, call your local University Extension center.

Moisture Levels & Testing

Moisture levels for safe storage of hay vary with size and density of the bale and type of hay. In general, hay in small rectangular bales should be baled at less than 22 percent moisture to keep molding and heating to a minimum. Large round bales retain internal heat much longer than conventional bales. Therefore, hay should be less than 18 percent moisture before baling in large bales. If you are storing or sheltering some of your big bales, this long-term heat retention affects the proper time to move big bales into storage. Hay baled with more than 22 percent moisture should probably not be put into storage for at least 30 days. This is especially true if bales are to be stacked several layers deep.

If hay has not been "sweated" properly due to rain and other bad weather and is more than 14% moisture content, mold and spontaneous combustion can be a problem. Smell the hay for freshness, and check the hay for moisture [see below]. Properly sweated hay is stacked for 21 days in the field and then stored in a hay barn. Hay barns are tall poles with a roof and open sides. The hay needs air circulation.

If the hay has been treated with sodium ascorbate, acetic acid, or proprionic acid as a preservative in damp or improperly cured hay, increased urination of the animals will become a problem if water intake is not increased. [note: apparently these act as diuretics in the animal if hay is too moist]. They are FDA and USDA approved preservatives in the USA.

Hay that is below 14% moisture has other problems, too little moisture, Hay can be as low as 11% moisture and still be palatable to most animals. Much below that is expensive straw and it really doesn't matter if it is grass hay or legume hay. Molds and dust can still be a problem even if the hay is too dry, don't be fooled by dryness.

To test for moisture content, do what the livestock people do. Take a handful of hay and twist it into a rope [try to spin it into thread]. If the twist falls apart immediately or breaks into many pieces, it is too dry and is valueless. If it stays tightly twisted and doesn't expand, then it is too wet and should be stored in an area that is open and has good air circulation. It should be used rapidly, or it will mold. Check it frequently for signs of mold, and smell it before using for freshness. Some molds will change the smell of the hay.

If the twist lightly opens but still holds its shape, then the hay has the correct moisture content, more or less. This hay can be used over a period of time. For horses it is recommended that hay be used within a 90 day period or less.

Electronic, hand-held moisture meters are not consistently accurate. These meters usually have a bale probe and windrow probe, and they depend on electrical conductivity between points on the probes. Inconsistent readings can occur when testing hay crops with relatively dry leaves and dry outer stems, but wetter inner stems. If such a problem occurs, a bale probe may give readings between 4 or 5 percentage points too low at the time of baling, depending on drying conditions and grass content.

Generally, the windrow probe has proven more accurate than the bale probe when it is used just prior to baling on a sample from the damper, bottom-side of the windrow.

However, the microwave oven and gram scale method of determining moisture appears to be the most accurate of all (see the accompanying description).

To determine hay moisture with the microwave oven and gram scale method, follow these steps:*

Step One. Fill in the blanks.

First weight of sample _____________ (a)

Last weight of sample _____________ (b)

(Note: These weights should not include the weight of the plate. Therefore, subtract the weight of the plate before going any further.)

Step Two. Complete this equation.

b a x 100 = percentage of dry matter.

Step Three. Complete this equation.

100 - percentage of dry matter = percentage of moisture in the hay.

*It might be a good idea to follow this procedure twice. First, follow the procedure with samples taken from an average spot in the windrow. Then run through it again, this time with samples taken from the wettest spots. That way, you become aware of the average moisture, as well as problem spots.

Maturity of Hay

Grasses, which are somewhat lower in feed potential than legumes to start with, follow the same decreasing pattern in feeding value as they mature. Grasses such as fescue and orchard grass will often be as low as 6 percent crude protein after blooming when the seeds are beginning to form.

Legume-grass mixtures should be harvested when the legume reaches the desired stage of maturity regardless of the growth stage of the grass.

If the plants are not under stress conditions, the recommended stages of maturity for harvesting common forage plants in Missouri are:

Storage Considerations

Grass hays [such as Timothy Hay and Sudan Grass] are good as long as they are free of insects, rodents, molds and weeds. The general storage period for them is 60-90 days. Grain hays [such as barley or oats] must be stored in a rodent and insect free area. If the heads shatter, the value of the hay is nothing. The pest and contamination problem [ergot molds etc.] and shattered heads are a major factor in the value of grain hays. Grain hays should be used within a month or you need to have lots of hungry cats around to keep the rodent population down. Remember, the grain head is the only part of value in a grain hay.

Legume hays [such as Lucerne/alfalfa] can be stored for as long as 6-9 months. Prebloom and bloom stages are the best quality. Moisture content is very important to the quality. As all of the plant is edible, you do get more for your money. With some of the legume hays, the estrogen content can be important. If you are having breeding problems, consult with the extension service or local Agricultural Ministry, or school. Remember, some legume hays like alfalfa [lucerne], the calcium oxalate can decrease calcium absorption in some animals. If you use alfalfa on a regular basis, you might want to consider supplementing the diet with a calcium rich food, such as calf manna.

I used the following references to compile this article - submitted by Kent Hall:

Jimmy C. Henning and Howell N. Wheaton
Department of Agronomy, University of Missouri-Columbia

University of Illinois at Urbana-Champaign

College of Agricultural, Consumer and Environmental Sciences

Cooperative Extension Service

North Dakota State University:

Randy Gaebe, Former Extension Agent
Greg Lardy, Beef Cattle Specialist
Karl Hoppe, Area Livestock Specialist