ARTIFICIAL Drying Provides Means of Preserving Feeding Value of Immature Grasses
The possibilities of growing large amounts of forage for feeding purposes, and utilizing it when 1n its immature stages, have been emphasized by the advent of the commercial forage-drying machine. The purpose of preserving forage in a relatively immature condition is to obtain a roughage feed of high protein and nutrient content. The dry matter of young rapidly growing forage is high in protein, minerals, and vitamins, and low in fiber content. As the stage of maturity advances, the nutritive value of the forage decreases. This results principally from a change in the chemical composition and from a reduction in the digestibility of the nutrients.
If a satisfactory method of preservation is developed, a much larger percentage of the dairy ration can be supplied in the form of home-grown feeds. If, for instance, pasture grass can be dried artificially at a stage of maturity at which it still contains a high percentage of protein, the grass by itself, or in combination with hay and silage, will make a complete ration for dairy cows in the winter, just as pasture makes a complete ration in the summer. It would be necessary, of course, when putting up forage in this way to cut it several times during the season. Drying by artificial means could be accomplished at a time when the grass is ready to be cut regardless of weather conditions.
Artificial drying of forages has certain advantages over the conventional way of making hay. It reduces waste through leaching and loss of leaves, and can be done regardless of weather conditions. The success and future development of this method of preserving forage crops depend upon (1) the cost of drying and (2) the effect of drying upon the feeding value of the dried product. Pasture is well adapted to frequent cropping, because of its perennial nature and its quickness in recovery. It is also one of our highest yielding crops. During the last 4 years the Bureau of Dairy Industry, in cooperation with the Western Washington Experiment Station and the Washington Agricultural Experiment Station, has carefully studied the nutritive properties of artificially dried pasture herbage and the effect of the drying process on its feeding qualities. The pasture contained a mixture of grasses and clovers and was cut when 2 or 3 weeks of age and dried in an experimental artificial drying machine.
The high protein content of pasture herbage when cut every 2 or 3 weeks, averaging in many cases as much as 24 percent, is maintained throughout the growing season. Moreover, this immature herbage maintains a relatively constant low content of fiber throughout the season. A minor significant item in its composition, as compared with that of drier and more mature forage, is its high calcium and phosphorus content. These elements tend apparently to be more concentrated in herbage when it is growing rapidly, particularly if well distributed rains occur during the growing season.
When artificially dried pasture grass exclusively was fed to dairy heifers, it proved palatable and highly nutritious. Two-year-old heifers consumed approximately 15 pounds of the dried material per day. This was sufficient for maintenance and some gain in live weight. The digestibility of the various nutrients was not affected by the drying process. The herbage contained a digestible crude-protein content of 18 percent and a total digestible nutrient content of 65 percent. In these respects it compared favorably with many high-protein concentrate feeds.
Using grass 3 weeks old, the investigators studied the effect of the temperature of artificial drying on the digestibility and availability of the feed nutrients. Pasture herbage was dried in the machine at exhaust-gas temperatures of 250°, 300°, 350°, and 400° F. When compared with rations of green and sun-cured grass, the grass artificially dried at different temperatures did not change in chemical composition, except that drying at 400° produced a significant increase in the crude-fiber content. This indicated that portions of the more leafy materials were burned. Furthermore, the herbage that was dried at 400° had a much lower coefficient of digestibility for protein and to a lesser extent for dry matter, crude fiber, and nitrogen-free extract, than herbage dried at lower temperatures. Apparently the intense heat reduced the availability of the calcium. Nutrients in grass dried at lower temperatures were as efficiently digested and utilized as those in green and sun-cured herbage. As the temperature of drying was increased, the percentage of natural color in the herbage was adversely affected. It was evident that raising the temperature in the artificial drier to extremely high levels, to get increased efficiency in the utilization of fuel, lowers the nutritive value of the feed.
Further experiments determined the vitamin D content of artificially dehydrated pasture grass, as compared with, that of similar grass fed in a green and sun-cured condition. When rats received green, artificially dried, or sun-cured herbage, in addition to a basal diet, they developed significantly higher percentages of ash in their bones than did rats receiving only a basal diet deficient in vitamin D. Either the green or the artificially dried grass produced calcification as efficiently as the herbage cured by exposure to 15 hours of sunlight. When fed as 3 percent of the dry matter of the ration, there was sufficient of the calcifying factor in the grass to cause an increase in the calcification of the bones in the experimental animals. Dehydration at high temperatures for a short time did not destroy the calcifying property of the herbage.
Two feeding trials were conducted in which dried grass was substituted for part or all of the grain mixture fed to milking cows. In the first experiment, cows in heavy production were fed, in addition to alfalfa hay and silage, a grain and grass mixture of which 20 percent was artificially dried grass. The cows ate slightly less grain-grass concentrate mixture, gained less weight, and produced a little less milk than when they received a similar ration in which wheat bran and linseed meal were substituted for the grass. The consumption of feed and total digestible nutrients per unit of production, however, was slightly in favor of the experimental mixture.
The addition of grass to the concentrate mixture made it rather bulky, though it was palatable and readily eaten. The comparative differences were small, and indicated that where an adequate supply of artificially dried grass is available it may be efficiently substituted for as much as 20 percent of the protein-rich concentrate mixture.
In the second experiment, 2 cows were maintained on a ration of alfalfa hay and artificially dried grass for 4 weeks and then switched to an all-alfalfa ration, as compared with 2 other cows that were put on an alfalfa-alone ration and then changed to an alfalfa-hay and dried-grass ration. The addition of dried grass to the alfalfa-alone ration of milking cows caused a greater consumption of total digestible nutrients. This greater consumption of nutrients produced a larger gain in live weight and a larger output of milk and butterfat. While the nutrient consumption per unit of production was approximately the same, the increased consumption of feed brought about by the addition of dried grass to the ration caused the cows to produce more milk.
This experimental work demonstrates that a home-grown feed palatable to dairy cattle, and having a high protein content, can be produced from pastures by frequent cutting and artificial drying of the herbage; that artificial drying within certain temperature limits does not affect the nutritive value of herbage either in the organic or the inorganic constituents; and that artificially dried pasture grass may be used efficiently with other roughage feeds, and as a substitute for protein-rich concentrates in the rations of lactatin, dairy cows. The cost for drying equipment is the major item which limits a more general use of this means of preserving forage crops for feeding purposes.