The need for improved utilisation of rice straw as feed for ruminants in Vietnam: An overview

Nguyen Xuan Trach

Department of Animal Production, Hanoi Agricultural University,
Gialam, Hanoi, Vietnam.

Abstract

Ruminant production plays an important part in the predominantly agricultural economy of Vietnam, especially in mixed animal-crop production systems. In addition to providing meat and milk for human consumption, large ruminants essentially provide draft power and manure for crop production. These animals themselves largely rely on crop residues as feed. The scarcity of land and the trend of sustainable agricultural development in the highly populated country necessitate better utilisation of crop residues in general and rice straw in particular for ruminant feeding. Although rice straw produced every year is plentiful, the amount a ruminant can consume is not sufficient to sustain a reasonable level of production due to its low nutritive value. Therefore, rice straw has not been maximally utilised for ruminant production yet. Suitable treatment techniques in combination with nutrient supplementation could result in improved utilisation of rice straw with better benefits. Despite recent local research in this field, no methods for improved utilisation of straw are practically applied by farmers in the country, probably because none has proved to be relevant and sustainable under the local physical and socio-economic conditions. Further studies are therefore needed to develop acceptable straw feeding systems.

Key words: rice straw, treatment, supplement, ruminants, Vietnam

Introduction

Vietnam is a tropical country with a crowded population of more than 76 million living on a territory area of 332000 sq. km. The rural community account for around 80% of the population, among these approximately 70% rely almost exclusively on agriculture for their livelihoods. Since the agricultural sector is so much important, its future performance will continue to be the main factor influencing the living standards of the majority of the Vietnamese (Ogle and Bui Huy Nhu Phuc 1997). However, due to high population pressure serious consideration is being given to the development of sustainable agriculture (Le Viet Ly 1996). Current trends towards sustainable agriculture under protection of the environment with the emphasis on decreased reliance on environmentally hazardous chemicals may result in lower yields of cereal grains. Production of grain eating animals will probably be faced with increased costs because of decreased availability of feed. Ruminant production should thus become more ecologically and economically justified owing to the possibility of using fibrous feeds such as grass and crop residues. However, due to the scarcity of land for grazing and grass cultivation, better utilization of crop residues in general and rice straw, which is produced in abundance in the country, in particular is required for the improvement of ruminant production in Vietnam.

The present paper provides an overview of the current situation of ruminant production and rice straw utilization in Vietnam with emphasises placed on nutritionally limiting factors. It thereby highlights the need for improved utilisation of rice straw. Possible approaches to improve the utilisation of rice straw as feed are discussed with reference to the particular context of Vietnamese small farmers. Recent local studies in this direction are reviewed and further research directions are recommended.

Current ruminant production and rice straw utilization

There are currently around 3.0 million buffalo, 3.8 million cattle, and 0.5 million goats in Vietnam (FAO 1998). Except for a few number of state-run farms, which are fairly large, most ruminants are in the hand of small holders. Dairy production is practised with almost only exotic purebred and crossbred cattle, which account for a very small proportion (15 000 heads) of the total cattle population and are raised mainly in some highland plateaus and in peri-urban areas. Intensive beef production has not been practically developed. The majority of cattle and especially buffalo are of indigenous breeds and kept as an integral component of the traditional animal-crop production systems (Figure 1).

The dominant integrated buffalo/cattle-rice production system has long existed in the agricultural country. On the one hand, buffalo and cattle contribute a lot to crop production by providing draft power and manure; on the other hand, they rely much on crop production which provides residues as their feed. Annual rice production increased from 11.8 million tonnes in 1976 (after country reunification) to 16.0 million tonnes in 1986 (agricultural reform) to 26.3 million tonnes in 1996 (ten years later), and still higher in recent years. Since 1990 Vietnam has become one of the biggest rice exporters in the world. The improved rice production together with increases in production of other major crops has been an important factor behind the rise in the numbers of ruminants and other main animal species (Table 1) thanks to increased quantities of surplus grains and agro-industrial by-products available as animal feed in the late 1980s and early 1990s.

Table 1: Rice and animal production in Vietnam
	1976	1986	1996
Paddy rice , 1000 tons	11827	16003	26300
Cattle, 1000 heads	1486	2784	3800
Buffalo, 1000 heads	2194	2658	2954
Goats, 1000 heads	189	432	513
Pigs, 1000 heads	8 800	11 796	16 921
Chickens, million heads	56.9	64.8	90.0
Ducks, million heads	28.9	26.4	44.0
Source: FAO (Internet Database, 1998)

Nevertheless, the population growth rates of cattle and especially buffaloes have recently slowed down. Whereas, the role of ruminants in providing meat and milk for human consumption should have been rapidly growing as a result of the increased living standards and disposable incomes of consumers. There is also an increasing demand for meat as well as live animals for export. Milk consumption was only 1 litre/person in 1991 (70 million litres) and of that 90% was imported (Cuong et al 1992). According to 1997 statistical data of the Department of Agricultural an Forestry Extension (Table 2), the proportion of ruminant liveweight in the total animal liveweight was still very small, compared to those of pig and poultry production. Although beef and dairy development has been part of a government strategy for food production, ruminant meat and milk produced per capita are still incredibly limited at present. In the mean time, it is known that large amounts of milk powder together with certain amounts of expensive beef have been increasingly imported recently. That is, ruminant production in Vietnam has not met the increasing domestic demands for meat and milk yet.

Better development of ruminant production in Vietnam is therefore highly needed; however, it is faced with considerable constraints of which feed shortage is of most concern. Traditionally, buffalo and cattle are bred mainly to serve crop production and kept mainly in the cropping areas. Due to limited arable land (about 0.1 ha per capita) priority is usually given to crops, there is little grazing land for ruminants. They are usually allowed for only strictly controlled access to grazing on roadsides, fallow land and the raised boundaries between the rice fields and other cropping areas. During the winter time when maximum draft power is required for land preparation under humid and cold weather, working buffaloes and cattle are fed almost exclusively on rice straw since the growth of the limitedly available grass is stunted. However, the amount of straw a ruminant can consume every day is not sufficient to sustain a reasonable level of production due to the low nutritive value of this highly lignified residue. The reduced availability and the poor quality of this feed usually result in reproductive disorders and loss of condition of the animals. It also is the main cause for many deaths of drafting animals in the winter working season. Thus, the most widespread technical constraint to increased ruminant production for farmers in the mixed crop-ruminant farming systems is their inability to feed animals adequately throughout the year. This is also true for the dairy industry due to seasonality in patterns of grass growth and forage supplies (Nguyen Xuan Trach 1989). By the same token, beef production would be suffering from short and uneven supply of feed. The pressure of feed inadequacy will be further increased when more ruminants are raised, to say nothing of arable land being reduced due to infrastructure development and urbanization.

Table 2: Animal products of Vietnam in 1997
Products	All species	Pigs	Poultry	Cattle & Buffalo
Liveweight:
- produce, 1000MT	1 007.9	729.0	178.9	111.9
- percentage, %	100.00	76.80	15.00	8.20
- Annual growth rate (1990-1997), %		6.85	3.84	1.48
Liveweight/capita:
- produce, kg	19.59	15.04	2.95	1.60
- percentage, %	100.00	76.80	15.10	8.10
- annual growth rate (1990-1997), %	3.67	4.60	2.54	-0.50
Fresh milk:
- produce, million litres				31.27
- produce/capita, litres				0.41
- annual growth rate (1990-1997), %				19.26
Eggs:
- total produce, million pieces			3 169.65
- produce/capita, pieces			41.3
- annual growth rate (1990-1997), %			7.71
Source: Le Ba Lich 1998

Rice straw produced every year is plentiful and, if well exploited, it could help overcome, at least in part, the shortage of feed to increase the number and performance of ruminants. Rice is the predominant food grain with 2-3 crops per year. Usually, it is estimated that approximately 1 kg of straw is produced for each kilogram of grain harvested (Devendra 1997). According to a case study recently carried out in the countryside of Hanoi on 5 rice varieties (Nguyen Xuan Trach, unpublished data), on the average 0.83 kg straw is produced together with each kilogram of paddy grains. Based on these figures, 25-30 million tonnes of straw could be expected every year now in Vietnam. However, straw has not been maximally utilised as feed for ruminants yet. Vast amounts of this renewable resource are burnt either in the field or as cooking fuel. Some is used for other purposes such as litter and mushroom production. Moreover, rice straw is usually fed untreated to ruminants without supplements in spite of the fact that many methods for improved utilisation of straw have been developed and recommended (see Sundstøl and Owen 1984; Preston 1995, Chenost and Kayouli 1997, among others) and that local research and extension activities in this area have been undertaken.

There are, perhaps, several reasons for farmers not yet to apply the already developed methods for improved utilisation of straw as feed. First, in addition to their poor understanding about ruminant nutrition and feeding, farmers have not been well informed and trained about the techniques. This is because there is no good linkages between agricultural educators, researchers, extension workers and target farmers. Second, risk aversion with respect to livestock production often results in a reluctance to adopt new technologies and thus priority is generally given to crop production in terms of labour use and cash investment as indicated by Ogle and Bui Huy Nhu Phuc (1997). Third, the ever-developed methods per se seem not technically and socio-economically suited to the local conditions under which small poor farmers are dominant. Consequently, as Preston (1995) once mentioned, increased production may not earn farmers sufficient income to pay for the treatment and, therefore, they lose interest and the technology is not taken up. This is in part because the prices of ruminant products are still low in Vietnam. Moreover, subsistence farmers have no cash-flow available to pay for inputs.

Possible strategies to improve straw utilization in Vietnam

The key to improve the use of crop residues for ruminants is to overcome the barriers to rumen microbial fermentation of lignocellulosics. The two well known factors of rice straw that limit bacterial digestion in the rumen are its high level of ligninification and low contents of nitrogen, vitamins and minerals. Therefore, in principle, there are two approaches, which should be taken in combination, being straw delignification treatment and nutrient supplementation. However, to develop any feasible strategies in a particular context, the local physical and socio-economic conditions must be taken into account. To follow, possible straw treatment and supplementation techniques to be studied and applied in Vietnam are discussed with reference to its circumstances.

Treatment

Numerous methods of physical, chemical, biological treatment have been worldwide researched and developed in order to improve the utilisation of straw and other fibrous by-products as feed for ruminants. Physical and biological treatments of roughage have received an appreciable amount of research, but no practical method has been successfully designed due to many difficulties in the development of useful and economical treatment processes. Biological approach may promise a new horizon for research, but it is, for the time being, too demanding and still early for applied research in a developing country like Vietnam. Industrial treatments which are energy dependent and thus costly should not be recommended for small farmers. Chemical treatment at farm level seems to be more practical.

Chemical treatment involves the use of alkaline, acidic or oxidative agents. Among these, alkali treatment has been most widely researched and appeared to be promising in Vietnam. According to the present state of knowledge, concentrated alkaline agents can chemically break the ester bonds between lignin and hemicellulose and cellulose, and physically make structural fibres swollen (Schiere and Ibrahim 1989; Chenost and Kayouli 1997). These effects enable rumen microbes to attack the structural carbohydrates more easily, increasing digestibility, and at the same time increasing palatability of the treated straw (Bod'a 1990). The most common alkaline agents ever used are sodium hydroxide (NaOH), ammonia (NH₃) and urea. Other chemicals with alkaline effects have also been tried.

A number of NaOH treatment methods have been developed as referred to in the reviews by Home (1984) and Berger et al (1994). The major advantages of the various NaOH treatment methods were high digestibility and palatability of treated straw (Sundstol 1984). Nevertheless, each method had one or some of the following drawbacks: threat to environmental pollution, high content of Na in the treated straw, and rather complicated facilities and procedures. Due to these concerns, in developing countries where, in addition, NaOH is too expensive and not widely available, the application of NaOH treatment seems to be out of question under an environmentally sustainable agriculture and for resource-poor small farmers.

Ammoniation of straw by means of anhydrous and aqueous ammonia, urea and other ammonia releasing compounds have also been widely studied as reviewed by Sundstøl and Coxworth (1984) and Berger et al (1994). The mode of action of ammoniation is assumed to be similar to that of NaOH treatment owing to the hydroxide group (OH^-). Besides, ammoniation increases the nitrogen content of the straw. Furthermore, ammonia has a preservative effect inhibiting mould development during treatment. As a result, in addition to increasing digestibility of structural carbohydrates, ammoniation is an effective means of decreasing the amount of supplemental nitrogen and increasing acceptability and voluntary intake of the treated straw by ruminants. Although comparative studies have shown that ammoniation is not as efficient in improving the energy value of the straw as NaOH, it has become popular in many countries (Sundstol 1984). However, pressurised containers and a well developed infrastructure are required for anhydrous and aqueous NH₃ treatments. Because of these shortcomings in addition to its limited availability, NH₃ can see little applicability in an agriculture-based developing country.

When urea is used, ammonia is released after urea has been mixed with water and straw in the confines of a silo, or some other structure. This is a much safer method than those requiring handling of anhydrous or aqueous ammonia (Berger et al 1994). Urea is a solid chemical, so it is easy to handle and transport (Sundstøl and Coxworth 1984). Another advantage of urea is that in many developing countries, it is considerably cheaper than NaOH or ammonia, and is much more readily available. Therefore, urea treatment should be of more interest. However, the use of urea alone is still an expensive way of supplying nitrogen to ruminants, as the level required for effective treatment of straw is some 50% greater than what is needed by the rumen microbes (Preston 1995). In addition, the price of urea is tending to rise due to reduced agricultural subsidies, which may put an end to the application of this method one day. Suppose that only 50% of the total rice straw produced annually in Vietnam was treated with 5% urea for ruminant feeding, an additional amount of approximate 0.75 million tonnes of urea would have to be imported for this purpose alone. Therefore, it is worth trying levels of urea application lower than usually recommended (4-6%) complementing it with cheaper alkaline agents.

Urine is an enormous and perpetual but usually wasted source of urea. As a source of urea, in principle, urine can also be used and has been recommended for treatment of straw. Urine can be sprayed on the straw in a similar way for treatment with urea solution (Dias da Silva 1993; Preston 1995). Urine treatment of straw has been reported to give nearly as good improvements in digestibility and nitrogen content as other methods of ammoniation given the same level of urea (Coxworth and Kulman 1978; Dias da Silva 1993). However, research works on this subject have still been rare and there is currently not enough available information to define clearly the conditions to optimise urine treatment (Dias da Silva 1993; Sundstøl 1993). So far, the urine/straw application rate has been somewhat arbitrarily made between 1/1 and 3/1 in different experiments in which information on the nitrogen content of the urine used was not available (Dias da Silva 1993). It is apparent that urine is a voluminous by-product with greatly variable contents of urea (Owen 1993), thus too much urine has to be collected for treatment and it is difficult to guarantee the quality of the treated straw. In addition, practical problems with urine collection and preservation as well as aesthetic, health and hygienic concerns should be taken into account. In Vietnam, farmers normally collect urine to make fertiliser for crops; therefore, they should have no aversion with collecting urine for straw treatment if this method is proved to be effective and safe enough. Treatment of straw with urine, if well organised, may serve as a practical method for small farmers to treat a by-product with another by-product in a sustainable agriculture.

Treatment of rice straw with lime (CaO/Ca(OH)₂) should be given priority for research at the moment since it is cheap and readily available. Lime is not only an alkaline agent, it can also be used to supplement calcium which has been found in negative balance in cattle fed on rice straw (Nath et al 1969). A number of researchers have studied the effect of treatment with lime on the quality of cereal straw. Results from available reports (Nath et al 1969; Dumlao and Perez 1976; Pacho et al 1977; Owen and Nwadukwe 1980; Verma 1981; Saadullah et al 1981a; Hague et al 1981; Bass et al 1982; Garmo 1984; Djajanegara et al 1984;  Hadjipanayiotou 1984; Pradhan et al 1997) seem to be equivocal. There have been two methods for straw treatment with lime: soaking and ensiling. From the data provided, it may be said that the soaking method was unsatisfactory in improving the feeding value of straw. Usually, digestibility was increased, but dry matter intake was decreased due to unpalatability. Lime is a weak alkali with low solubility, thus ensiling for longer periods of time seems to be required for effective treatment of straw. Recent studies by Pradhan et al (1997) showed that ensiling rice straw with 4% or 6% Ca(OH)₂ gave higher in-vitro dry matter digestibility (IVDMD) than with 4% or 6% urea. However, heavy mould growth was observed in the Ca(OH)₂ treated straw, as also observed in previous studies on barley straw (Owen and Nwadukwe 1980; Bass et al 1982; Hadjipanayiotou 1984). Furthermore, the problem of unpalatability due to high levels of lime (and magnesium in it as well) should still remain there.

It seems that a combination of lime with urea would give better effects than urea or lime alone. Such a combination would take advantage of highly increased digestibility and calcium supplementation due to lime and the well known alkaline and preservative effects together with the increased nitrogen content of straw due to urea. Additive effects of two chemical have been demonstrated (Saadulah et al 1981b; Verma 1981). Therefore, the levels of application for both lime and urea in combination can be considerably reduced. Moreover, additional effect may be achieved as calcium hydroxide enhances the decomposition of urea into ammonium hydroxide (Van Soest 1994). By experiment, Zaman and Owen (1995) have drawn a conclusion that mixtures of Ca(OH)₂ and urea would be the alternative chemicals to NaOH or ammonia for improvement of the nutritive value of straw. Pradhan et al (1997) have also found that addition of urea to Ca(OH)₂ improved the IVDMD. Comparing a number of treatment inputs, Sirohi and Rai (1995) have shown that a combination of 3% urea plus 4% lime at 50% moisture for 3 weeks reaction time was the most effective treatment for improving digestibility of paddy straw. Apparently, this area warrants further detailed research, especially in vivo and on-farm studies to evaluate animal responses.

Supplementation

Supplementation with biologically effective supplements which are locally available should be a strategy for better utilisation of rice straw. Untreated straw may at most support only the maintenance requirements of the ruminant. Treated straw without supplements can support production levels far below the level potentially made available by the increase in digestibility and intake due to treatment (Preston and Leng 1987). This is because rice straw is not only highly lignified, but also has low contents of nitrogen, minerals and vitamins. Therefore, as Chenost and Kayouli (1997) pointed out, it is necessary firstly to provide the rumen microbes with the nutritive elements which they need for self-multiplication and for degradation of the cell walls of straw, and following this, to ensure all conditions for maintenance of good cellulolysis. In order to allow the animal to develop target performance levels, one must also ensure additional supply of nutritional elements for production, but this should not hinder the cellulolytic activity of rumen microbes.

In Vietnam, there is a great variety of byproducts which can be utilised as feed supplements. The annual production of rice bran from paddy rice processing is around 1.0 million tonnes. Production of protein feed sources amounts to 10 000-15 000 tonnes of fish meal, 10 000-20 000 tonnes of soy bean and 20 000-25 000 tonnes of various types of oil cakes such as groundnut, soy bean and coconut (Le Viet Ly 1996), 7500 tonnes of cottonseeds (FAO 1998). All of these byproducts can be well incorporated into straw-based diets for better responses from ruminants. In addition, mineral and vitamin supplements may be made commercially available to ruminant holders.

Supplementation of straw in Vietnam may be in the form of

• Supplements consisting of only urea,
• Mixtures of molasses and urea,
• Multinutritional blocks,
• Supplements with green forages and crop residues,
• Supplements using local byproducts

For details of these methods of supplementation one may consult Chenost and Kayouli (1997).

Recent local research for better utilisation of rice straw

In response to the high need for improved utilisation of rice straw as feed for ruminants, studies on straw treatment and supplementation have recently been carried out in the country. The following works can be referred from local and international publications.

At laboratory level

There have been experiments on the effect of ammoniation on chemical composition of straw. Nguyen Trong Tien (1993) followed changes in chemical composition of rice straw treated with urea as affected by levels of urea application (0, 3, 4 and 5%) and times of incubation (0, 10, 30, 60 and 90 days). A similar study was carried out by Nguyen Xuan Ba (1997) with 0, 3, 4, and 5% urea and 0, 10, 20, 30, and 60 days of incubation. Both authors concluded that dry matter (DM), crude fibre (CF) and crude protein (CP) of straw reduced over the time of incubation and that urea treatment increased CP and reduced CF of treated straw as compared with untreated straw. Based on the results of these studies, straw treatment with 3% urea was reasonable and the incubation time should be at least 10 days, but not exceed 30 days. Nguyen Xuan Trach et al (1998) also analysed a number of factors (urea level, moisture content, treatment duration) affecting chemical composition of urea treated straw. Their results indicated that treatment duration from 10 to 30 days and the water/straw ratio form 0.5 to 1/1 did not differently affect NDF and ADF contents of 5% urea or 3% urea plus 0.5% lime treated straw. However, the fixed nitrogen content increased significantly after 20 days of treatment and in 5% urea treated straw compared with 3% urea plus 0.5% lime treated straw. In a study with cattle urine, Nguyen Trong Tien (1991) found that urine ammoniation also reduced CF and increased CP contents of rice straw.

In situ studies

A few in situ studies on fistulated cattle have been undertaken to determine rumen degradability of straw and microbial development as affected by urea treatment. Dang Thai Hai and Nguyen Trong Tien (1995a) examined degradability of dry matter (DMD), crude fibre (CFD) and crude protein (CPD) of straw ensiled with 3, 4 or 5% urea at 50% moisture content for 21 days. It was found that DMD, CFD and CPD were all improved due to urea treatment and that CFD and CPD were significantly increased when the urea level increased form 3% to 4 % and 5%, but DMD was not significantly different between the various levels of urea application. These authors (Dang Thai Hai and Nguyen Trong Tien 1995b) also reported that 3% urea supplementation or 3% urea treatment of straw fed to cattle increased the number of bacteria in favour of cellulolysis; however, the population of protozoa was not significantly affected by the supplementation or treatment with urea.

Feeding trials

Feeding trials have been conducted for beef cattle. Nguyen Kim Duong et al (1996) showed increased straw consumption and liveweight gain in growing cattle fed on 4% urea treated straw supplemented with cotton seed cake and molasses compared with those of cattle fed on untreated straw sprayed with 4% urea and given the same supplements. Vu Van Noi and Le Viet Ly (1996) demonstrated in one experiment that liveweight gain was nearly doubled when grazing crossbred calves were given urea treated rice straw together with molasses urea block. In another experiment they found major improvements in growth rate of grazing crossbred calves additionally given urea treated rice straw plus molasses and cotton seed. Bui Van Chinh and Le Viet Ly (1996) reported encouraging results on growth rate and feed intake of crossbred beef cattle fed on rice straw treated with 2.5% urea, 0.5% lime and 0.5% salt. Nguyen Xuan Ba (1997) compared 4% urea treated straw, 4% urea sprayed straw and untreated straw fed to grazing crossbred cattle and found that daily gains and feed intake were highest for those fed 4% urea treated straw, followed by 4% sprayed straw and untreated straw. However, in the above studies, no economic evaluation was indicated and it was not possible to dissect out the components of the diet and their specific effect on growth rate.

To improve household dairy production in Ho Chi Minh city, Doan Duc Vu et al (1997) replaced untreated straw in the diets of lactating cows with 4% urea treated straw alone or 4% urea treated straw together with multinutritional blocks. In both cases, straw intake and milk yield were significantly increased. As a result, the economic profits were also enhanced, especially for low producing cattle (<15 litres/day). The combination of urea treated straw and multinutritional blocks brought about better results in terms of milk yield and economic profits, compared with feeding urea treated straw alone. In the countryside of Hanoi, Nguyen Thi Luong Hong (1995) substituted 20% green forage in the routine diet of lactating cows with 2% urea treated rice straw. The results showed that milk yield was increased (by 15.1%) and milk quality was improved (higher fat and protein contents, lower acidity).

Based on studies with buffaloes, Nguyen Van Thu et al (1994a) indicated that giving molasses-urea cake to native buffaloes in the Mekong river delta fed on rice stubble and straw improved health and productivity. Studying effects of multinutritional cake supplementation on performance of growing and working local buffaloes and cattle fed on straw or straw and grass diets, these researchers (Nguyen Van Thu et al 1994b) concluded that supplement cakes containing urea, molasses, rice bran, coconut oil meal, salt, bone meal and trace elements supported good health and working capacity of native cattle and buffaloes in areas where feed and water shortages occurred. In addition, Thu et al (1996), reporting several on-station and on-farm experiments, showed that 4% urea treated rice straw either fed alone or together with urea-molasses cake resulted in increased nitrogen content of straw, feed intake, health status, draught power and milk yield of working and dairy buffalo compared with those of buffalo fed on untreated straw as controls.

Although there have already been laboratory experiments, in sacco studies, on-station and on-farm trials in Vietnam, most of the research works have so far been carried out separately and devoted mainly to urea treatment which has been widely researched in the rest of the world. There is still a lack of systematic research into straw treatment and supplementation from laboratory to production. There have not been comprehensive comparative studies on biological and economic effects of different treatment and supplement inputs including those locally available other than urea to suggest the best or alternative solutions. Neither are there currently any information on the quantity and quality of straw from local cultivars of rice. Rice breeders have so far concentrated their efforts only on improved paddy grains for direct consumption of humans.

Conclusions and recommendations

Ruminant production has had and will continue to play a very important role in Vietnam. However, its further development is confronted with major problems related to the scarcity of grazing land and low quality of crop residues which are the major sources of available feed for ruminants. Improved utilisation of rice straw and other crop residues would be a strategic solution to encourage farmers to increase both the numbers and productivity of their ruminants, meeting the traditional demand for crop production and the increasing demand for livestock products. The question arisen then is what are the strategies that can be technically and socio-economically relevant and acceptable to farmers under the local conditions. Despite encouraging results of several techniques which have been developed, none has yet been proved to satisfy all biological, practical, economical and environmental requirements.

To be sustainable an acceptable feeding system for improved rice straw utilisation should be simple, machinery-independent, use cheap and freely available inputs, and easily fit into the farmer normal routine (Sundstol 1984). In this perspective, further research should be directed to treatment of straw with locally available inputs such as urea, urine, CaO or Ca(OH)₂ and their combinations. It is also important that treated straw be soundly supplemented with protein-rich byproducts such as fish meal, cotton seed or oil cakes as well as necessary minerals and vitamins. In addition, there should be studies on the quality and quantity of crop residues as ruminant feed to provide information for plant breeders to develop crop cultivars which can produce large amounts of high quality residues without at the expense of grain yield and quality.

Acknowledgements

The author is very grateful to Prof. Frik Sundstol, Noragric, Agricultural University of Norway, for his valuable comments on the first manuscript of this paper.

References