|Bioconversion of Organic Residues for Rural Communities (UNU, 1979)|
|Indian experience with treated straw as feed|
Straw, like all mature plant tissue, is relatively indigestible by the micro-organisms that inhabit the digestive tract of ruminants, This is because straw cell walls are heavily lignified or silicified. The objective of straw treatment is to increase digestibility by disrupting the cell wall. A number of methods have been developed, all of which have been described in detail by Jackson (4). These methods may be classified as chemical, physical, and biological. The chemical methods all involve the use of alkali solutions and are the most widely tested methods at present. Among the physical treatments, only pressure cooking alters the cell wall; simple grinding does not increase digestibility. A promising method of biological treatment is the growing of lignin-digesting fungi on straw. In the Indian village context, the feeding of alkali-treated straw will usually require the simultaneous feeding of additional nitrogen, as it will be the limiting nutrient in straw for both ruminant digestion and growth and production of the animal. As feed nitrogen is extremely scarce, the use of a urea supplement is an essential adjunct to straw treatment.
Sen et al. (5) experimented with the Beckmann method of straw treatment using wheat and paddy during the Second World War. In this method, straw is soaked for about 20 hours in 10 to 201 of a 1.5 per cent NaOH solution per kg straw, and subsequently washed with large volumes (up to 50 I/kg) of clean water to remove residual alkali. The results of the Sen et al. experiments (5) were similar to those from experiments conducted in Europe at the same time (6); the digestibility of the straw was increased by an average of 25 percentage units - from 40 - 50 per cent to 65 - 75 per cent. In spite of its effectiveness, this method of straw treatment did not become widespread in Europe, mainly because costs were too high. Some 8 kg NaOH are needed per 100 kg straw and the yield of treated straw is only 75 per cent.
In India, cost was not a factor (see Table 1, for example), but even so it never came into widespread use. Many state departments of animal husbandry began straw treatment by the Beckmann method on their livestock breeding farms, but it was not continued for long, and it was never really introduced into villages. There are several reasons for this. The units set up on livestock farms were ail small-scale, manual treatment installations that were too small for herds of 100 or more animals. The Beckmann straw treatment method gained ground in Norway only in the 1950s after a mechanized installation was designed (7), a development which did not occur in India. In any case, even if it had, the treatment of straw on a handful of government farms would not have much significance for the bulk of Indian livestock, which is owned by small farmers.
The reason the Beckmann method was never adopted by small farmers in India is primarily that new practices have to be demonstrated on the farm to convince farmers of their usefulness, and in the 1940s and early 1950s there were no organizations that could do this. The very concept of on-farm demonstrations of animal husbandry practices, though introduced two decades ago (8), did not receive any attention until very recently (4). A purely technical problem would probably severely limit the spread of the Beckmann method of treatment - it requires huge amounts of water. In many villages water is scarce.
In the early 1950s, Kehar (8) demonstrated the value of Beckmann-treated straw for animals maintained in villages by their owners (Table 1). The heifers with which he did his experiment were fed only very limited amounts of supplemental feeds, and even these supplements were given irregularly. The heifers suffered all the vicissitudes of a poor village environment. The simple treatment of the straw in their diet nearly doubled the rate of weight gain.
TABLE 1. Comparative Costs of Feeding Growing Heifers Untreated and Treated Paddy Straw (Beckmann Method) in Rural India
|Straw consumption (kg/day, dry straw basis)||3.00||3.00|
|Feed cost (Rs/head/day)||0.36||0.56|
|Liveweight gain (kg/day)||0.10||0.18|
|Days to gain 100 kg||1,000||555|
|Feed cost/kg gain (Rs)||3.60||3.11|
Source: Kehar (8).
Much more could probably have been achieved if a supplement of urea had been fed along with the treated straw, and if the straw had been fed ad libitum. These results are noteworthy for two reasons. First, they indicate that straw treatment can be profitable under village conditions. Second, it was the first, and probably still the only, example of what has now come to be considered an important technique for testing new animal husbandry practices. The need for on-farm testing of straw treatment techniques is emphasized later.
In the late 1960s, a simple spray method of alkali treatment was developed. Some of this work was done in India (9, 10). This was an improvement over the Beckmann method in that less alkali is used (only about 4 kg/100 kg of straw), no washing is necessary, and recovery is 100 per cent. On the other hand, digestibility increases by only about 10 units on average. Greater increases in digestibility are theoretically possible with higher levels of alkali (up to 8 kg/100 kg of straw), but animals cannot tolerate such large amounts of sodium. Improved rates of weight gain in growing calves of 0.1 - 0.15 kg/head/day have been found by treating straw by this method (see, for example, data in Table 2) (11). The economics are also favourable, as the table shows.
TABLE 2. The Performance of Calves on Untreated and Treated (Spray Method) Straw Diets
|Straw consumption (kg/day)||4.5||6.0|
|Groundnut cake consumption (kg/day)||0.8||1.0|
|Feed cost (Rs/head/day)||0.95||1.39|
|Liveweight gain (kg/day)||0.25||0.42|
|Days to gain 100 kg||400||238|
|Feed cost/kg gain (Rs)||3.80||3.31|
|NaOH energy input (MJ) additional energy stored as body-weight gain (MJ)||12.1**|
|NaOH energy input (MJ)
total energy stored (MJ)
|NaOH energy input (MJ)total protein energy stored (MJ)||5.0***|
Source: Singh et al. (1 1).
* Straw was treated with 3.3 kg NaOH/100 kg straw.
** For the method of calculating this value, see Annex 2.
*** Protein energy content of the gains made by the calves is assumed to be half the total energy stored.
On the basis of this limited information, a set of recommendations for farmers has been prepared (Annex 3). A few progressive farmers here and there are treating their straw with this method. Demonstrations of straw treatment (alkali and urea) have also been done on animals in one dairy development project, and some experience has been gained. On the whole, however, there is a need for further testing under village conditions. A proposal for doing this has recently been made and is described in a later section. The exercise presented in Annex 4 indicates the type of evaluation of straw treatment that should be made, and the information that needs to be generated.
Two newer methods, more effective than the spray treatment, are potentially applicable under Indian village conditions, and experimentation has already begun on these. One is the modified Beckmann, also known as the Torgrimsby method. Straw is soaked as in the original Beckmann method, but washed in a fixed amount of water, which is then recycled. Straw is effectively treated as in the original method, but residual sodium is less completely removed. Recovery is 100 percent. Two digestibility trials to date have yielded increased digestibility values of 15 and 18 units. Further work is in progress in India (D.V. Rangnekar, personal communication, 1978) as well as in Europe (F. Sundstol, personal communication, 1978).
The second method is spray treatment and stacking. If the amount of NaOH solution applied to the straw is kept low (not more than 10 - 151/100 kg of straw), and the straw is stacked (minimum size of stack 3 tons), the heat generated in the chemical reaction between the alkali and the straw causes a temperature rise in the stack. This temperature rise increases the efficiency of treatment (units increase in digestibility/kg of NaOH used). To apply such small amounts of solution uniformly, specially designed treater-mixers must be used. Such treater-mixers have been designed for use in factories and for on-farm use in Europe. Capacity is 2 - 6 tons/hour.
A small machine, operated by a 5 hp electric motor and giving an output of 0.3 tons/day, has been developed in India (12). Farmers always stack their straw after threshing; it is envisaged that they could put it through this machine at the time of stacking. Many farmers already have an electric motor on their pump or wheat thresher that could be used on a straw treater. Manufacturing cost without the motor is about Rs 3,000. Evaluation of straw treated in this way is in progress.
Supplementation of Straw with Nitrogen and Minerals
It has been conclusively demonstrated that treated straw will not be digested to its full potential digestibility if the nitrogen content of the diet is below 1.2 per cent (E.R. Orskov, personal communication, 1977) (13). This corresponds to rates of supplementation of 1.5 per cent for urea or 10 - 15 per cent for oilcake. These levels of supplementation must be ensured if straw is to be treated. From the point of view of the ability of the animal to utilize the energy available from treated straw, these levels of supplementation must be considered a bare minimum. Under average village conditions, animals, particularly growing animals, do not receive even this level of 1.2 per cent nitrogen in the diet from the meagre supplements of grass/forage and milling offals they are fed. Thus, a urea supplement is an essential adjunct to straw treatment. Further experimental work on this subject is proposed in a later section.
In many parts of India, animals suffer from deficiency diseases such as rickets and anaemia. Some progress has been made in mapping these areas. General purpose mineral mixtures are now widely available, although still not as widely used as they might be. Obviously, where a mineral is the first limiting factor for productivity, increasing energy intake by straw treatment will be futile.