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During the interval from cutting until the forage is dry enough to keep in storage, a progression of events promotes losses and deterioration of the quality and feeding value of the forage. These field losses generally originate from three sources: Respiration and fermentation (chemical and bacteriological), mechanical damage, and weather damage. The amount of destruction caused by the three factors varies according to conditions and determines the amount of field losses. Field operations should be managed to keep these factors to a minimum.
Freshly cut forage is living material. The plant cells continue to respire, and plant enzymes continue active for some time after the crop is cut. In addition, micro-organisms naturally contained in the forage continue activity as long as air is present and shore is sufficient moisture These fermentation processes affect principally the soluble carbohydrate fractions and the carotene. If drying is prolonged, however, important losses in dry matter and protein may also occur. Losses amounting to 5 to 15 percent of the total crop have been found to occur from so-called field fermentation losses.
The methods of handling the forage in the field should be designed to promote the most rapid evaporation of moisture so that these losses may be kept to a minimum.
Hay that is drier than it need be for safe storage is very susceptible to leaf shattering, and such hay usually is graded lower in quality because of lack of leaves.
Leaching and bleaching also cause losses when forage is dried in the field. Rain falling on partly dried forage produces losses that result from shattering of the leaves and from the leaching of soluble nutrients from the forage. Various workers have shown that hay that has been rained on is lower in protein, nitrogen-free extract, and carotene and higher in crude fiber than hay not rained on. Rain promotes mold development and this also contributes to nutrient loss and lowered feeding value. Excessive exposure of forage to the sun increases its vitamin D value but causes a decrease in color and carotene content.
Field-cured hay generally will sweat after it is stored. If it is undercured, it will heat in the mow and this heating produces losses in dry matter and feeding value. Frequently such hay will lose 5 to 15 percent of its dry matter and nutrients while in storage. If heating is excessive in the mow, brown and black areas of charred and burnt hay may develop and, as is all too frequently the case, heating may continue until spontaneous combustion occurs and the hay and storage barn are burned. Brown and black hay appears to be palatable to livestock, but numerous investigations have shown that this type of hay has a decidedly lowered feeding value.
When partly dried forage is placed on a barn hay finisher, it is still wet enough to allow rapid fermentation to take place. Air moving through the mass of hay carries with it the moisture evaporated from the forage. The temperature of the air will govern how much moisture it will pick up. Heated air will pick up more moisture than unheated air, and drying will be hastened if the air is heated before it enters the drier. The heat created by fermentation may also increase the temperature of the air and thereby increase its water-holding capacity. It is important to spread the forage evenly over the drying system and to have the same degree of packing throughout. The air will then flow evenly through the forage and the hay will dry thoroughly in all parts of the mow. The hay dries from the bottom up, and when the top layer is dry enough to prevent heating, the lower layers are even drier.
The drying should be completed as rapidly as possible to retard fermentation. The longer fermentation takes place the greater the losses of dry matter and nutrients because optimum temperature and moisture conditions are present for microbiological activity.
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