In contrast to cereal grains, roughages generally are low in readily available carbohydrates. The amount of lignin is a critical factor with respect to digestibility. Lignin is an amorphous material which is associated closely with the fibrous carbohydrates of the cell wall of plant tissue. It limits fiber digestibility, probably because of the physical barrier between digestive enzymes and the carbohydrate in question.
The protein, mineral and vitamin contents of roughages are highly variable. Legumes may have 20% or more crude protein content, although a most of may be in the form of nonprotein nitrogen (NPN). Other roughages, such as straw may have only 3-4% crude protein, most others fall between these two extremes. Mineral content may be exceedingly variable; some roughages are relatively good sources of calcium and magnesium, particularly legumes. The phosphorus content is apt to be moderate to low and potassium content high; the trace minerals vary greatly depending on plant species, soil and fertilization practices.
Roughages are sub-divided into two major groups; dry and green or succulent roughages based upon the moisture content. Green roughages usually contain moisture from 60- 90%, whereas, dry roughages contain only 10-15% moisture. For the sake of convenience, succulent feeds are again classified into various types such as pasture, cultivated fodder crops, tree leaves, roots, and crops. Dry roughages have been further classified as hay and straw, based on the nutritive values and methods of preparation.
A method of conserving green crops is that of haymaking. The aim in haymaking is to reduce the moisture content of the green crop up to 15-20%, to inhibit the action of plant and microbial enzymes. Thus, a green crop in a mature stage is preserved for a long time.
Indian hay is seldom taken in the same in which this term is understood in the western countries. It consists of dry grass on which the seed has ripened and leaves have usually been shed. In feeding value, it mostly corresponds to the straw of cereals rather
than to hay made before the seed has ripened. Fig. 2.1 Legume Hay
During the later part of the monsoon season, when
the grass is ready to be cut for hay (the only time when grass is available for haymaking), the weather is often so wet that haymaking cannot be attempted. At the end of the monsoon season when there is still some chance of making hay from some good quality grasses that may be left, cultivators are too busy in making preparation for rabi sowing. According to the type of forages which are dried, hays are categorized as leguminous, nonleguminous and mixed.
Good legume hay has many characteristics that make it of special value to the dairy cattle. It has a higher percentage of digestible nutrients. It has more digestible proteins because of the high protein content. Furthermore, the proteins of legumes are of superior quality, as compared to proteins from other plants. Well cured legume hays are higher in vitamin contents. They are particularly rich in carotene and may even contain vitamin D. They are also a rich source of vitamin E. The legume
hays are particularly rich in calcium and generally palatable. Among various leguminous fodder crops lucerne, berseem, cowpea and soybean hays are considered first.
Non-legume hays made from grasses are inferior to legume hays. They are, as a rule, less palatable and contain less proteins, minerals and vitamins than the legume hays. Non-legume hays have the advantage over legume hays because their outturn per hectare is more than that of legume hays and the former can be grown easily. Hays made from green crops like oat and barley, compare very favorably with the other grass hays. For making good quality hay, these crops should be harvested in the milk stage. They are low in proteins and minerals, but rich in carbohydrates.
Hay prepared from mixed crops of legumes and non-legumes is known as mixed hay. The composition of such kind of hay will depend on the proportion of the different species grown as a mixed crop. Such a crop is generally cut earlier because of the variation in the seeding time of the mixed crops. If harvested early, cereals are generally richer in proteins.
Inadequate production of green fodder in the country compelled the farmers to utilize dry roughages as livestock feed particularly for the ruminants. In one estimate, it has been found that in the country, there are about 310 million tones of these dry roughages produced annually. Among these straw, bhusa, Karbi and hay are noteworthy. In all developed countries, feeding of high-quality hay is in practice. Due to unavailability of high-quality dry roughages, straw, bhusa and Karbi form the major bulk of livestock feed in India. Obviously, feeding of inferior quality
dry roughage is reflected in the low productivity of animals.
Fig. 2.3 Wheat straw
Farmers utilize these poor quality dry roughages as energy feed, which unfortunately varies between 40-50% in digestible energy. Voluntary intake of animals is so low that it is barely sufficient to yield adequate energy to meet their maintenance needs. For some roughages, more energy is spent by the animal in chewing and digesting the roughages than what the animal derives from the dry roughages.
The poor nutritive value of these roughages may be attributed to the following facts:
- The digestibility of straw is limited due to the formation of strong physical and/ or chemical bonds between lignin and the structural polysaccharides (hemicellulose and cellulose). Although cellulose by itself has a highly ordered crystalline structure, it has a very strong association with lignin with the result that even most the potent cellulosic enzymes can not have easy access to the cellulose unless the bondage between lignin and cellulose are broken. The lignin thus acts as a barrier in the efficient utilization of cellulosic plant materials even as a source of Whether, the inhibitory mechanism involves the presence of lignocellulosic or ligno-hemicellulosic chemical bonds or the three dimensional macromolecular lignin network by itself acts as a protective barrier in the efficient utilization of cellulose as a source of energy is yet fully understood and established
- The crystalline structure of cellulose is also responsible for low digestibility of
- Highly deficient in other nutrients like minerals, vitamins, fatty acids and in proteins. The minimum crude protein requirement for efficient lignocellulose breakdown of roughages fed as the sole diet is claimed to be from 8-5.0%
- The high silica content of straws known to depress organic matter digestibility
- Due to dustiness of straw, the total intake is markedly affected
Paddy and wheat straw are by-products available after harvesting the grains, form the main bulk of roughages in the tropical region, including India. They form the staple feed for cattle and buffaloes throughout the region. Though they are poor in nutritive value, containing about 3% protein and 40-45% TDN, these straws can maintain adult non-producing cattle as a sole feed along with small quantities of protein supplements. However, certain factors like high lignin content, reduced palatability, dustiness, high oxalic acid content in straw which limits calcium absorption, limit their extensive use as cattle feed.
Most common pulses are (1) Urad/black gram (Vigna mungo), (2) Moong/green gram (Vigna radiata), (3) Moth (Phaseolus aconitifolius), (4) Cowpea (Vigna unguiculata), (5) Masoor (Lens culinaris), and (6) Arhar/program/pigeon pea (Cajanus cajan). After harvesting, seeds of pulses are threshed out of the pods to split to form dals used extensively as a protein adjunct to an otherwise starchy diet of the human population. The husks of the pods with leaves and tender stems are left behind as by-products and can be utilized as fairly nutritious cattle feeds.
Among the above-mentioned straws, those of urad, moong, and moth are highly palatable and nutritious, straws of arhar and masoor, although of comparable nutritive value, are not as palatable as the other three straws. The energy value of these straws is comparable with those of cereal straws but they are a fairly good source of digestible protein.
Cereal straws like wheat bhoosa and paddy straws contain 3% digestible protein and 40% TDN and can meet the maintenance requirements of adult cattle and buffaloes. Since these by-products (pulse straws) contain from 40-100% more of DCP, they can as well meet the production requirements of the animals to the certain extent. Supplementation with energy-rich feeds like cereal grains will, however, be necessary in the case of high milk producing cattle.
Groundnut is the major oilseed produced in India. At the time of harvesting, large quantities of leaves and stem become available for the feeding of livestock. Extensive studies were conducted on the groundnut bhoosa as a partial substitute for concentrates in the ration of milk cows. It is understood that in large parts of India, groundnut straw is commonly fed to livestock.
The DCP value of groundnut straw is superior to that of non-leguminous hays and is comparable to that of leguminous hay of cowpea. In energy value, as represented by TDN, groundnut straw is superior to most of the grass hays. It can be safely fed along with wheat bran and wheat straw to meet entire nutritional requirements of milch cows producing up to 5 kg of milk daily.
Being quite fibrous and good in nutritive value than pulse straws and groundnut straw, it should be fed in limited quantities in conjunction with cereal straws to non-productive animals.
It contains 4-6% crude protein, 51% crude fiber, 77% NDF and 62% ADF.