Steam treatment

Steam treatment of crop residues under pressure has recently opened a new vista for their nutritional improvement especially in the situation when steam availability is cost effective. This technology is based on the hydrolytic action of high temperature steam that breaks chemical bonds, and causes various degradations that enhance the digestibility of residual product. Steam is available inexpensively at sugar mills where one of the major sugarcane byproducts i.e. bagasse can be treated conveniently. Steam pressure treatment on sugarcane bagasse, paddy straw and sorghum straw at low pressures (5, 7 and 9 kg/cm2) for relatively low treatment times (30 and 60 minutes) demonstrated the positive effect on DM digestibility, most noticeably on bagasse and sorghum straw.Keeping in view the necessity of improving the nutritional upgradation of crop residues, chemical or physico-chemical processing have been investigated more vigorously during the past decades in India and the objectives of the investigation include:

•  Cost effective technology
•  Easy availability of chemicals and other inputs
•  Easily adaptable technology
•  Environment friendly technology
•  A technology applicable at small and large scale.

Many attempts have been made to achieve the objectives of using chemicals ranging from alkalies (NaOH, NH3, urea, Ca (OH)2), acids (sulphuric acid) and oxidizing agents (e.g. bleaching powder) and their various combinations not only in India but also in various foreign laboratories.
Ligno-cellulosic bonds, the main hindrance in releasing the energy from crop residues, are labile to the alkali treatment and thus the alkali treatment helps in increasing the availability of energy to the animals. For this purpose sodium hydroxide was employed successfully and proved to be an effective agent to increase their energy value, but this technology was not found favourable due to the following reasons:

•  Cost of treatment
•  Corrosive nature of sodium hydroxide
•  Excessive load of chemical on kidney of animals to excrete the sodium.
•  Increased soil alkalinity as a result of mixing sodium rich urine
•  Need for the supplemental nitrogen

Since rumen microorganisms require nitrogen also for their growth and active functioning, ammonia (NH3) though a weak alkali, may prove more effective for straw improvement especially in the situation where animals are not provided enough nitrogen source. The effectiveness of NH3 for upgradation of straws depends upon its level, temperature, treatment time, moisture and the quality of material taken for  improvement. Since handling and transportation of gaseous ammonia is hazardous, the urea has been widely investigated as a source of NH 3  during the course of ammoniation of crop residues and the results from Indian laboratories showed that 4% urea (straw DM) and 40% moisture and a treatment period ranging from 10 to 30 days under closed conditions is most effective. The comparative utilization of ammoniated and untreated wheat straw in a long term feeding trial had shown better productive performance in cattle and buffaloes which has been reviewed in the International Workshop held at NDRI, Karnal under Indo-Dutch Bioconversion Project. However, when the freshly harvested paddy straw ensiled with urea (4%) was fed to buffalo calves as an exclusive source of dietary nutrients, the digestibility of CP was very low. Similarly, some other experiments also showed the poor utilization of nitrogen from ammoniated straw. But, when the straw was supplemented with urea as such at much lower level (2% of straw DM) the utilization of nitrogen was better than that from ammoniated straw. The effectiveness of ammoniation for improving the available energy of digestible straws was doubtless in all the experiments.

The economical analysis of ammoniated straw feeding has revealed that it is economical to feed calves of all the age groups and up to 5 liters of milk production in lactating animals. At higher level of milk production, ammoniated straw did not prove economical until it was supplemented with green fodder, concentrate mixture/bypass nutrients to meet the nutritional needs. In spite of effectiveness of ammoniation technology, it could not arouse desirable response from the farmers when it was demonstrated at their door-step. Lack of adoption of this technology is attributed to the requirement of additional labour and cost, slow production response and the scarcity of feeds during the season (summer) when farmers give priority to the harvesting and preparation for the next crop.

Among the various chemical treatments, urea/ammonia treatment of straw has clearly emerged as the most effective, practically feasible and relevant technique under tropical conditions. It is moderate in rendering the straw more digestible as well as palatable. Urea treatment at 4% increases the CP content of straws from 3 to 8 % and the TDN content from 40 to 55 %. The increase in milk yield reported by farmers ranged from 0.25 to 1.0 kg /day, on feeding of ammoniated straw. The response of the animals depends upon the availability of nutrients from other feeds. The technology is more effective in areas, where green fodder is not available. However, the poor response to this technology under field conditions is perhaps that the farmers feel that it is a labour intensive technology. Since the technology is useful in increasing the productivity of animals, may be it requires some more refinement and educationbefore it is again transferred to the field.

In the rumen, partial breakdown of lingo-cellulosics takes place mainly through the enzymes, produced by the diverse microorganisms. Plant fragments entering the rumen or hind-gut become extensively colonized by bacteria within an hour with a preference on the damaged areas during primary colonization. These bacteria have limited capacity to break down the cell-wall structure and lignin is not accessible to them. But in nature lignin is degraded by fungi as a result of oxidative process. Among  fungi, white rot fungi breaks the lignocelluloses bonds to some extent with less utilization of cellulose, the most important component of cell-wall. Therefore, single stage or double stage solid state fermentation technology was explored to upgrade the nutritive value by biological treatment using various species of fungi in various laboratories world over including India, where sizable work was carried out under Indo-Dutch project on bioconversion of crop residues. It was found that biological treatment of crop residues improved the nutritive value at the expense of precious cellulose and hemi-cellulose, which resulted in DM loss up to 20% during the biological treatment. Moreover, this technology can not be adopted by the farmers due to the intricate process and complex technical know how.

Ragi (Eleusine coracana) straw is being used without any processing under field conditions, which results in quite a substantial wastage, mostly of stem portion. It’s chopping with or without water soaking will enhance its utilization and reduce the wastage. Ragi straw (as such) was treated with urea solution. One type of straw was dried under sun, while the other type was ensiled in moist condition for 21 days. Feeding of treated straws improved the digestibility of dry matter and organic matter over untreated straw but highest values were observed with moist straw, which was attributed to the softening of straw due to moisture and also to the breaking of lingo- cellulosic bonds as a result of ammoniation.