ENSILING HAY AND PASTURE CROPS

J. B. Shepherd, R. E. Hodgson, N. R. Ellis. J. R. McCalmont

MAKING part of the hay and pasture crops into silage has several advantages.

The grasses and legumes usually grown for hay and pasture are mostly biennial or perennial and are produced more cheaply than annual or cultivated crops. Silage can be made from them with about the same equipment (except a silage cutter) and labor that is needed for haymaking.

Because the crops are taken off the field and put into the silo soon after they are cut, there is little risk of weather damage during harvesting. About 80 to 85 percent of their value (as shown by experiments at Beltsville) is preserved for feeding; only 70 to 75 percent of the value of field-cured hay is preserved, even if it is made during good curing weather. Properly made grass silage will provide much more protein and several times more carotene in the ration than field-cured hay, increase materially the carotene and vitamin A content of winter milk, and help prevent an oxidized flavor in winter milk.

Surplus pasture herbage and heavy or weedy crops that might make only low-grade hay can be made into a palatable, nutritious silage, thus preventing waste. Silage is the best form in which to preserve surplus forage crops from one year to the next as insurance against drought. Ensiling also destroys the germinating powers of weed seeds and thus helps eradicate weeds from the farm.

Storing forage as silage ends the hazard of fire from spontaneous ignition of inadequately cured hay. Less space is needed to store crop dry matter as silage than as long, baled, or coarsely chopped hay. Silage is an easy form in which to feed forage to livestock; grass silage is particularly useful for feeding cattle and sheep.

About half of 1 percent of the American hay crop was ensiled in 1944 roughly equal to 1,500,000 tons of silage but relatively little as compared with the more than 40,000,000 tons made yearly from corn and the sorghums. In the Northeastern States, 1.6 percent of the hay crop was put into silos in Massachusetts, 3.3 percent, and in Rhode Island 4.6 percent. But as farmers turn more and more to grassland farming and as they learn more about making grass silage and the advantages of feeding it, we believe the amount of the silage made from hay and pasture crops will increase greatly.

Many crops can be made into silage: Timothy, bromegrass, orchard-grass, Sudangrass, Kentucky bluegrass, Johnsongrass, succulent range grasses, alfalfa, soybeans, lespedeza, red clover, Ladino clover, cowpeas, kudzu, alsike clover, crimson clover, and others, even though they differ widely in physical characteristics, in chemical composition, and in yield, as well as palatability.

Some of them can be ensiled in the same manner as corn or the sorghums. Others need a somewhat different kind of treatment.

Legumes or grass and legume mixtures usually make a more nutritious silage than do grasses alone. Adapted, high-yielding crops are the most satisfactory. Especially suitable for use as hay, pasture, or silage are combination crops such as alfalfa with timothy or bromegrass, and timothy, bromegrass, or orchardgrass with Ladino clover and red clover or alsike clover.

A rule of thumb is that crops that are palatable when grazed or fed green or as dry hay also make a palatable silage. Likewise, crops that are unpalatable when grazed or fed green or dry are usually unpalatable as silage. Furthermore, feeding trials conducted with some crops indicate that the dry matter contained in silage of good quality will have about the same feeding value as an equal quantity of dry matter in good-quality hay made from the same crop, and better than the dry matter contained in poor hay.

The transformation of green crops into silage is brought about by the changes that take place when the green forage is stored in a silo in the absence of air. Plant respiration, enzymes present in plant cells, and bacteria, yeasts, and molds present on the crop when it is ensiled all take part in this change.

After the crop is ensiled, plant respiration continues until the oxygen present in the air and trapped in the forage is used up and replaced by carbon dioxide and nitrogen. There follows a rise in the temperature of the forage, the extent of the rise depending upon the amount of oxygen present.

Enzymes are also active during this time. They break down sugars into alcohol, carbonic acid, water, and acetic, lactic, and butyric acids. The enzymes act on proteins to some extent, forming amino acids, peptides, and some ammonia.

As plant respiration and the activity of the plant enzymes slow down, the activity of the bacteria, yeasts, and molds increases. Molds cease growing as soon as the air is exhausted, yeasts soon disappear, and only the bacteria remain active thereafter. Bacteria produce additional acid from soluble carbohydrates and from alcohol, and are responsible for further break-down products from the other constituents of silage, notably protein. They are responsible for most of the losses of dry matter and feeding constituents that occur during fermentation and storage.

When the acidity of the silage increases beyond a certain point, bacterial action diminishes, and the silage-making process is completed.

The Massachusetts Agricultural Experiment Station found wide variations in the type of fermentation, the kinds of acids produced, and the quality of the silage. Many investigators have learned that the type of fermentation produced and the quality of the silage produced can be modified by suitable methods of silage making. They also learned that the inclusion of acids and sugars or other readily available carbohydrates at the time of siloing modifies the type of fermentation, increases the acidity, and tends to reduce the breakdown of protein compounds. Thus the farmer can control pretty well the fermentation process and produce good grass silage from many crops under many conditions.

Standards by which the quality of silage may be judged were set up by the American Dairy Science Association committee on silage methods in 1942. These standards are :

a. Very Good: Clean, acid odor and taste, no butyric acid, no mold, sliminess or proteolysis, acid pH of 3.5 to 4.2, ammonia nitrogen less than 10 percent of total nitrogen.

b. Good: Acid odor and taste, trace only of butyric acid, acid pH of 4.2 to 4.5, ammonia nitrogen 10 to 15 percent of total nitrogen.

c. Fair: Some butyric acid, slight proteolysis or some mold, acid pH 4.5 to 4.8, ammonia nitrogen 15 to 20 percent of total nitrogen.

d. Poor: High butyric acid, high proteolysis, sliminess or mold, acid pH above 4.8, ammonia nitrogen about 20 percent of total nitrogen.

Several factors influence the type of fermentation produced, the nature and extent of the losses occurring during fermentation and storage, and the quality of the silage produced. Among them are the maturity and chemical composition of the crop, the ratio of soluble carbohydrates to the mineral base content of the crop, its percentage Of moisture when stored, the rapidity and completeness with which air is excluded from the silo, and atmospherical temperatures when the crop is ensiled.