Cassava hay production and its supplementation effect on swamp buffaloes (Bubalus bubalis) in LOA PDR; a review of the literature
 

Ammaly Phengvilaysouk

Table of contents

 

Cassava production in Lao PDR.. ……………………………………………………………………………..1

Nutritive values of cassava foliage and root2

Cassava hay and root as a ruminant feed. 3

Buffaloes production systems in Lao PDR.. 4

uffaloes management in lowland areas. 5

Buffalo management in sloping land zones. 5

The importance of buffaloes in small-holder farming systems. 5

Supply of meat and milk.

Advantage of draft power and manure

Role of cassava hay supplementation for swamp buffaloes

Role of cassava hay supplementation for swamp buffaloes

Feed intake and digestibility of swamp buffaloes

Rumen ecology of swamp buffaloes

References

Cassava production in Lao PDR

The Lao PDR is a land-locked nation that lies within the watershed of the Mekong River. Approximately 80% of the land surfaces are hills and mountains. There are three main agro-ecological zones consisting of uplands, plateau and lowlands. The uplands are mountainous regions from 1,100 to 3,000 m altitude (60% of the total land area). The plateau ranges from 800 to 1,300 m and the lowlands are plains less than 800 m above sea level (Bouahom, 1995). The Lao PDR is seasonally tropical, with a pronounced wet and dry season. The lowest levels of mean annual rainfall are about 1,300 mm in the northwest, while the highest level is 4,000 mm in the Annamite range in the south. The majority of the lowlands have 1,500 to 2,000 mm annual rainfall (BCR, 2003).

Lao PDR has about 5 million hectares of land that is suitable for cultivation. Of these only 800,000 hectares are planted with rice or secondary food crops by farmers. Around 750,000 hectares are used as pastureland and 50,000 hectares for ponds for freshwater fish farming (MAF, 2002). In the uplands, complex soils, which are strongly leached and acidic, predominate. Soils in the lowlands are usually highly weathered, with moderate acid, and classified texturally as loams, sandy loams and loamy sands. These soils tend to be of low in organic matter content and have therefore a low cation exchange capacity and low base saturation. High levels of aluminium and iron are found in some soils, which have a low water-holding capacity that makes them prone to drought. Deficiencies of nitrogen and phosphorus are widespread. However, cassava can grow in poor soil and can withstand drought. It is an important reserve crop in countries with unreliable rainfall.

Cassava is a plant that originated from South America and is known under various names: Manihot esculenta, manioc, yucca and tapioca, andbelongs to the family Euphorbiaceae. The tubers are high in starch that can be used as animal feed and for human consumption, while the leaves have high protein content. They are important in many developing countries in Africa, South and Central America, India and Southeast Asia (Food Safety, 2005). In Laos, cassava is mostly grown on small farms, usually intercropped with vegetables, sweet potatoes, melon, maize etc. In the traditional cultivation, there are two common varieties of cassava; the bitter and sweet. According to CIAT (2001) cassava is currently the third most important crop in Laos, after rice and maize. It is widely grown throughout the country by upland farmers but in small areas using local varieties and with very low inputs. The roots are used mainly for human consumption and for feeding livestock. Recently, the use of cassava root and leaf has increased. In 2001, researchers conducted experiments on cassava production at Houy Khot station in Luang Prabang Province and the Livestock Research Center (NamSuang) in Vientiane Province. Eight varieties were introduced from Thailand and two local varieties were planted. Cassava root yields were highest (20 to 25 tonnes per ha) for varieties Rayong 72 and Rayong 90, and 13 to 15 tonnes per ha for two local varieties at Houy Khot, while, cassava root yields were highest (25 to 30 tonnes per ha) for varieties Rayong 72, Rayong 60 and KU50, versus 15 to 20 tonnes per ha for the two local varieties at Namsuang (Vongsamphanh, 2003). In addition, several research projects have been carried out on the use of cassava foliage to feed animals: fresh foliage and DM yields ranged from 0.8 to 13.8, and 0.3 to 4.0 tonnes per ha, respectively. The differences could have been due to differences in planting space, study site and subsequent harvestings (Chantaprasarn and Wanapat, 2005).

Nutritive values of cassava foliage and root

Cassava roots are very starchy and therefore rich in carbohydrates, a major source of energy. In fact, the cassava plant is the highest producer of carbohydrates. It has been reported that cassava can produce 250 x 10³ calories per ha per day compared to 176 x 10³ for rice, 110 x 10³ for wheat, 200 x 10³ for maize, and 114 x 10³ for sorghum, according to UNU (1980). The chemical composition of cassava varies in different parts of the plant, different varieties and it also depends on the location, age, stage of harvesting, method of analysis, and environmental conditions. Although cassava roots are rich in calories, they are grossly deficient in protein, fat, and some minerals and vitamins. Consequently, cassava has lower nutritional value than cereals, legumes, and even some other roots and tuber crops, such as yams. According to UNU (1980) the cassava root contains from 64 to 72% carbohydrates, which are mostly starch, mainly amylose and amylopectin, and about 17% of sucrose is found in sweet varieties, and small quantities of fructose and dextrose. The lipid content of cassava is only 0.5 %. Cassava roots are poor in proteins (1-2% CP), and the amino acid profile of the cassava root is very low in some essential amino acids, particularly lysine, methionine and tryptophan. However, fermentation of the roots resulted in protein enrichment from 6 to 8%. Cassava is reasonably rich in calcium and vitamin C, but its thiamine, riboflavin, and niacin contents are low. Generally, cassava tubers are traditionally processed by a wide range of methods, which reduce their toxicity, improve palatability and convert the perishable fresh root into stable products; these methods consist of different combinations of peeling, chopping, grating, soaking, drying, boiling and fermenting (Tewe, 1991).

Cassava leaves are much richer in proteins than the roots. Although the leaves contain far less methionine than the roots, cassava-leaf has protein claimed to be superior to soybean protein. Cassava leaves are used as a protein source when the roots are harvested, but their intake and digestibility are low due to the high level of condensed tannins (Reed et al., 1982; Onwuka, 1992). However, harvesting of cassava foliage at an early growth stage (3 months) to make hay reduces the condensed tannin content and increases the protein content to 25% of DM. Crude protein in cassava hay has many essential amino acids similar to most vegetable proteins and with very low hydrocyanic acid, as stated by Wanapat et al. (1997). On the other hand, cassava leaves contain on average 21% crude protein, but values can range from 16.7-39.9% (Ravindran, 1991). Khuong and Khang (2005) found that fresh cassava foliage (DM basis) harvested at 45 days of re-growth contains 20.1% DM, 21.5 CP,7.8 Ash, 28.8 ADF, 38.2 NDF and 3.5% CT as compared to 20.2 CP, 36.4 ADF and 51.1% NDF in the experiment reported by Khang and Wiktorsson (2004). This wide variability is related to different cultivars, state of maturity, sampling procedure, soil fertility and climate. Almost 85% of the crude protein fraction is true protein (Eggum, 1970). The use of cassava in livestock feeding has been limited, due to the fact that cassava contains cyanogenic glucosides in the form of linamarin (93 per cent), and lotaustralin (7 per cent). The amount of cyanogenic glucosides varies with the part of the plant, age, variety and environmental conditions such as soil, moisture, temperature, etc. Certain varieties of cassava have long been designated as sweet or bitter in relation to their cyanogenic glucoside content. The sweet varieties are supposed to be much lower in HCN content than the bitter varieties (Wanapat et al., 1997).

Cassava hay and root as a ruminant feed

Cassava has one important characteristic, it can be managed to maximize production of carbohydrate (in form of roots) or protein by harvesting the leaves. For root production the growth cycle is from 6 to 12 months, at the end of which the entire plant is harvested. However, when maximum protein production is the aim, the foliage is harvested at 2 to 3 month intervals by cutting the stems at 50 to 70 cm above the ground, thereby encouraging the plant to re-grow. Dual-purpose production systems are also possible whereby one or two harvests of the leaves are taken before the plant is allowed to continue the normal development of the roots, as reported by Preston (2001). In addition, studies by Wanapat et al. (1997; 2000a; 2001) revealed the potential uses of cassava leaf and hay as a good source of protein. This was achieved by collecting the leaf or whole crop at an early stage of growth, and the harvesting of further biomass throughout the year. The accumulated yield of cassava hay ranges from 2 to 8 tonnes of DM per ha, depending on the variety, cultivation practice, use of fertilizer and soil moisture (Wanapat, 2001a).

Cassava is an annual tropical tuber crop, which is nutritionally valuable as a source of energy and protein for animals. Both fresh and dried cassava roots are consumed in different forms by ruminants (chopped, sliced, or ground). Dried cassava roots gave satisfactory results as the principal energy source for dairy cattle, intensive beef fattening and lamb growth. Cassava can replace almost all of the grain in the diets with little reduction in performance. Inclusion levels of up to 65%, preferably pelleted, do not seem to affect animal health, carcass quality or overall performance when the diets are carefully balanced. Palatability can be enhanced by the addition of molasses if pelleting is not possible (Animal Feed Resources Information System, 2006).

The protein content of cassava leaf and hay is relatively high, while fiber levels are low. Moreover, levels of the essential amino acids, methionine and threonine are similar to those found in soybean meal. Cassava bushes three to four months old are harvested by cutting about 40 cm above the ground and chopping in small pieces by hand or in a stationary forage chopper to use as foliage for cattle and other ruminants (Plant Guide, 2005). Cassava leaf or hay contains 20 to 25 percent crude protein in the dry matter and has minimal hydrocyanic acid (HCN) content, according to Wanapat et al. (1997), who recommended the use of cassava hay (leaves, stems and petiole) for feeding to ruminants. Wanapat et al. (1989) reported that cassava hay, as supplement to rice straw diets, increased rice straw intake, growth rates and digestibility in cattle and buffaloes. Supplementation of cassava hay to basal diets of untreated rice straw, cassava chips and cassava residues increased benefits to farmers (Viet and Kien, 2005).

Cassava hay contains tannin-protein complexes, which can act as a rumen by-pass protein and be digested in the small intestine. Therefore, supplementation of cassava hay at a level of 1 to 2 kg per head per day for ruminants could markedly reduce concentrate requirements. The condensed tannins contained in cassava hay have also a potential to reduce gastrointestinal nematodes; Kahn and Diaz-Hernandez (2000) emphasized parasites as a serious problem for ruminants in the tropics. Barry and Manley (1984) and Reed (1995) found that condensed tannins in the feed at more than 6% of dry matter reduce feed intake and digestibility; a CT level between 2 to 4% of DM helps to protect protein from rumen digestion and thereby increases rumen by-pass protein. Condensed tannins and protein can form a tannin-protein complex (TPC) by hydrogen bonding, especially under alkaline conditions. TPC is stable at pH 3.5-7.0, but the complex will dissociate at pH<3.0 and pH>8.0 (Jones and Mangan, 1977). In addition, cassava hay is an excellent multi-nutrient source for animals, especially because of its high level of protein. Nutrient availability can be improved by grinding and chopping. Overall, cassava has the potential to increase the productivity and profitability of sustainable livestock production systems in the tropics (Wanapat and Devendra, 1999; Wanapat et al., 2000b; 2000c and Wanapat, 2001a).

Buffalo production systems in Lao PDR

Swamp buffalo is indigenous in Lao PDR, and the majority originated from stock domesticated within Lao PDR, nearby China and Vietnam, and can be considered as an indigenous or traditional breed (MAF, 2001). Most swamp buffaloes are completely grey in color, and only a few are white. Normally, buffaloes have a lower heat tolerance than cattle, are slate gray, droopy necked, and ox-like with massive swept back horns. They wallow in any water or mud pools they can find or make. The swamp buffalo which is commonly seen in Laos is larger than native cattle, with males reaching 450 kg and females 350 kg. Females tend to have their first calf at four to five years, but calving intervals are lower than for cattle. Some reports put the annual calving rate at less than 50% (NAFRI et al., 2005). Commonly, buffalo is long lived and female buffalo can produce healthy offspring with an age above 20.

In Lao PDR, water buffaloes are predominantly of the swamp type, raised in extensive low input systems that take advantage of naturally occurring feed. The greatest difference is encountered between predominantly lowland areas in the Mekong corridor zone and the upland areas of the slopping land zones. Buffalo and cattle are mostly found in the central region, where they graze on vacant cropping areas for most of the year, but they also graze extensively in the sloping lands zone (FAO, 2003). Devendra et al. (1997) reported that the country is endowed with native pasture grazing areas, and out of a total of 8.5 million ha, 2.4 are found in the low lands, 0.4 are found in the plateaus and 5.7 million ha are found in the upland areas, respectively.

Figure 1. Number of large ruminants by province in the Lao PDR ('000) [Sources: JICA-MAF (2001),  Agricultural Census (2000)]

Buffalo management in lowland areas

Livestock is an important component of smallholder farms in lowlands areas of Lao PDR. Sales of livestock account for more than 50% of cash income in many upland areas. Over 95% of livestock is produced by smallholders (NAFRI et al., 2005). Buffalo density is high in the central and southern regions where a higher proportion of lowland rice is grown. This is the usual trend for areas in Southeast Asia where rice is harvested only once a year.

In these areas, buffalo are grazed on available cropping areas, forest, communal lands, etc. In general, buffaloes depend mainly on rice straw, stubbles, and re-growth of rice after harvest, and grasses and weeds growing in and around fields. The management systems are extensive, with animals being allowed to graze and mix freely in large herds. During the rice growing season, animals graze in the upland and the forest areas away from the rice fields to avoid crop damage. They are also tied around the household and fed with rice straw. The amount of available grazing and other non-cropping areas are critical for animal production since there are no other feed resources during this time of the year. Most villages in the Mekong Corridor have access to such areas, which are grazed heavily during the wet season. Management inputs are minimal with animals grazing in small groups. When buffaloes are needed to prepare land, they are kept near the rice fields (often tethered) and are fed grass, rice bran and sometime sticky rice to ensure that they are strong enough for land preparation.

In areas where irrigation enables farmers to grow two rice crops per year, buffaloes can only graze the cropping areas for a few months during the year. Therefore, they depend on other grazing resources for most of the year. This limits the number of animals that can be raised in these areas. Growing crops out of the normal growing season also requires more herding and supervision of the animals to avoid crop damage. More and more farmers invest in hand-tractors for land preparation and transport in intensive agricultural areas, and often sell their buffaloes to finance this investment. Due to this buffalo numbers are declining in many lowland areas (ILRI, 2002). On the other hand, the management of health is minimal; some may be vaccinated against certain infectious diseases, but most are not. Farmers have little interest in bovine vaccination, except when disease outbreaks take place. Common infectious diseases in bovines are foot-and-mouth disease of type A, O, Asia-1, and Haemorrhagic Septicaemia is very serious in buffalo. In addition, internal parasites such as Strongeloides and Neoascaris are also found in buffalo (Chantalakhana and Skunmun, 2002).

Buffalo management in sloping land zones

The sloping land zones include the upland and mountainous areas. Buffaloes graze extensively in fallow upland fields, grazing areas and forests. Management inputs are minimal for most of the year. Buffalo and cattle production occurs mainly in mixed crop livestock farming systems in the sloping lands zones rather than in the Mekong Corridor. The reasons are feed resources limitation in the lowland areas while in the sloping lands zone, more extensive grazing is available, and the resources are ideally suited to breed and supply buffaloes and cattle (ILRI, 2002).

In these areas, the traditional knowledge is different among the ethnic groups and villagers; therefore the buffalo management differs between areas. The Hmong are well known for their skills, they build extensive fences using local materials to keep animals from cropping areas during the wet season. Many villagers herd buffalo communally in designated grazing areas. In other villages, families manage animals individually. For one part of the year, animals graze in remote areas where ample feed is available. At other times, animals are brought back to pens every night. Farmers in some villages provide additional feed to buffalo with newborn calves and keep sick animals in special pens where they get cut-and-carry feed. Most farmers provide salt to animals, often as an incentive to return to the enclosure by themselves (NAFRI et al., 2005)

The importance of buffaloes in small-holder farming systems

Most Asian countries are agrarian, with 60-80% of the population engaged in farm operations in one way or another. Livestock has been an integral component of traditional agriculture for many centuries in Asia (Nanda and Nakao, 2003). Livestock production is firmly based in the smallholder farmers in both the Mekong Corridor and the Sloping Lands. Nationally, about 30% of cash income from agriculture was derived from livestock in 1997/98. In general, the importance of livestock as a source of cash income is highest in upland areas with poor access to markets where villages have to carry goods over long distances to markets. This limits options to crop with a high value per unit weight and livestock such as buffaloes and cattle that can be walked to markets (ILRI, 2002). Livestock provides many on-farm benefits; they are also a source of savings to be sold when cash is needed. Only when households accumulate enough livestock to feel financially secure are they able to make long-term investments in their farming and livelihood systems (e.g. sending children to high school, planting fruit trees, buying a two-wheel tractor or micro rice mill), buffalo play a pivotal role in the overall social development of small farmers. It is the main source of draft power to cultivate crops and prepare paddy rice fields, the main fertilizer and meat-milk supply for small farmers in mountainous area (Tuyen and Ly, 2001)

Supply of meat and milk

Buffalo meat has a lower content of saturated fat than beef and pork, and 40% less cholesterol, 55% less calories, 11% more protein and 10% more minerals as compared to bovine meat, and therefore, it is healthier. The quality has been markedly improved with the crossbred in Australia, which it is hoped will be the future standard in the 'Tender buff program' which has gained much popularity in recent years (Lemcke, 1997). Buffalo milk is healthier, because it is richer in saturated fatty acids. It is high in total solids (18-23%), that make it useful to make into cheese, butter fat, and several kinds of traditional sweets and ice creams. Swamp buffalo milk has even higher fat (9-15%), protein (7.1%), lactose (4.90%) and ash (0.89%) according to work by Thac (1979). Riverine buffaloes produce more milk than swamp buffaloes. The average lactation yield in the best known dairy buffalo breeds, Murrah and Nili-ravi, is around 2000 L (Agarwal and Tomar, 1998). Elite buffaloes with up to 6000 L also exist in India, Italy and Pakistan; this indicates their great potential for milk production. Working swamp buffalo produce 1.94 kg/day in Thailand (Khajarern and Khajarern, 1990) and 1.55 kg/day in Vietnam (Thu, 1997) while a non-working swamp buffalo may yield 2.15 kg/day (Gongzhen, 1996), and crossed with Murrah can yield of 3.73 kg/day in 277 days lactation.

Advantage of draft power and manure

Using buffalo for ploughing is definitely cost efficient in rain-fed lowland mixed farming systems (Bunyavejchewin et al., 1994). Based on profits produced over the investment, a pair of buffalo is 2.6 times more efficient than a tractor (Thu et al., 1995). Advantages include fuel savings, low maintenance costs, high resale value, use of otherwise useless crop residues, reduced dependence on external inputs and solidarity with sustainability. Also, buffalo values increase over the years and they need no costly fuel, maintenance, and they reproduce (FAO, 2000). Comparatively, machines require considerable monetary investment and are usually much larger in size than required by a peasant (Chantalakhana, 2001). Buffalo for work can start at approximately 2 years of age or at 250 kg bodyweight. Young buffalo can pull an approximately 50-80 kg plank or log in a plowed field together with a trained buffalo. They are subjected to work for approximately 1 h per day, gradually increasing to 3-4 h daily. The average buffalo learns to obey commands within 3-4 weeks (Saadullah, 1998). The power and efficiency of animals is increased with age and gain in bodyweight. Buffaloes normally carry up to a 2.0 t load, but can pull more than six times their own bodyweight continuously for 2-3 h, totaling 5-6 h daily in summer and 6-8 h in winter (Acharya, 1988).The average buffalo works up to the age of approximately 11 years. In Thailand, buffaloes work on average 5 h per day for up to 146 days per year. Draft buffalo work approximately 109 days/year in Vietnam (Sanh et al., 1995). In China, one buffalo is sufficient to do all the work on 2-3 hectares of cultivated land. Swamp buffalo plow 0.30 ha/pair per day and harrow 0.73 ha/pair per day (Thu et al., 1995).

Buffalo manure is an excellent source of nutrients for crops. Approximately 40% of the value of an animal could be in the manure it produces (Hoffmann, 1999). An adult buffalo produces 4-6 tonnes of wet manure per year. Normally, dung is heaped to mature for a few months and spread onto fields to maintain soil fertility. Farmers in South-East Asia spread it in the early rainy season and plow down before planting rice (Devendra and Pezo, 2002).

Role of cassava hay supplementation for swamp buffaloes

In all countries of Southeast Asia, large ruminants are fed on low protein diets and for a major part of the year are fed on crop residues and mature grasses. These forages are often deficient in crude protein and minerals. It should be possible to solve this problem by supplementation of an extra protein source, particularly cassava foliage. Cassava hay contains condensed tannins (CT) and proanthocyanidins (PC), which are common in tropical plants. CT are polyphenolics, which can easily be solubilized in water and can precipitate protein. The presence of condensed tannins and protein can result in the formation of tannin-protein complexes (TPC) by hydrogen-bonding, especially under alkaline pH conditions. TPC maintains its complex at pH 3.5-7.0, and will dissociate under pH 3.0 and over 8.0 (Jones and Mangan, 1977). Condensed tannins have been found to increase N-recycling in the rumen and saliva (Reed, 1995). Moreover, they improve rumen ecology, especially through enhancing microbial protein synthesis (Makkar et al., 1995; McSweeney et al., 1999; Makkar, 2000).

In the absence of supplemental sources of bypass protein from cassava leaf meals which have condensed tannins at optimal levels to protect proteins from degradation in the rumen (Leng, 2005). Wanapat (2001a) discovered that the condensed tannins (CT) contained in cassava hay at levels of 3.05-4.20% are beneficial for ruminants. Condensed tannins can protect proteins from fermentation in the rumen and hence increase the supply of amino acids to the small intestine (Kiyothong and Wanapat, 2003). Wanapat et al. (1997) reported that condensed tannins in cassava hay form a complex with the protein, so that much of the protein escapes the rumen fermentation which contributes amino acids directly to the animal.

However, in the tropical countries cassava is usually grown for root harvesting, so cassava leaf is a residue from cassava root production. Dried cassava leaf has successfully been used as supplement for ruminants fed straw based diets and increased rice straw intake according to Wanapat et al. (1992). This result agrees with Vongsamphanh and Wanapat (2004) who summarized that supplemented cassava hay increases both intake of rice straw and total DMI, while Leng (1997) concluded that cassava hay supplementation to native cattle, fed a rice straw basal diet and a rumen supplement, improves feed intake, rumen ecology and digestibility. Anexperiment was conducted on farm with supplemented cassava hay (500 g/head/day), which increased the growth rate by 50% and improved the feed conversion by 16% in local beef cattle fed on rice straw diets in the winter season in North Vietnam (Viet and Kien, 2005).

Recently, attention is now being focused on the potential use of whole cassava crop in integrated livestock production systems. In Thailand, the cassava research programmes are mainly focused on converting the cassava foliage into hay with the aim to reduce the risks of HCN toxicity (Wanapat, 2001a). The results of several experiments showed that cassava hay supplementation could replace concentrate fed to dairy cows (Wanapat et al., 2000b), and could reduce the level of nematode worm infestations in grazing buffaloes (Neptana et al., 2001).Providing a good source of roughage like cassava hay increases the ratio of protein to energy, and hence increases productivity in ruminants.

Role of coconut oil supplementation for swamp buffaloes

Dietary fats supply energy, carry fat-soluble vitamins (A, D, E, K) and are a source of antioxidants and bioactive compounds. Fats are also incorporated as structural components of the brain and cell membranes. Coconut oil consists of highly saturated fat (over 90%) and is rich in lauric acid. Saturated fatty acids are more digestible in ruminants than in nonruminants (Palmquist and Jenkins, 1980). Scientific Psychic (2005) reported that coconut oil is a common fatty acid which contains 8% unsaturated fatty acids 6% oleic (C18:1), and 2% linoleic (C18:2) acid. Coconut oil also contains 92% saturated fatty acids, including 6% capric (C10:0), 47% lauric (C12:0), 18% myristic (C14:0), 9% palmistic (C16:0), and 3% stearic (C18:0) acid.

Several studies were conducted to find out the appropriate utilization of oil, particularly supplementation to large ruminants. Wanapat et al. (2005) stated that energy in diets containing cassava chips and cassava hay are still low in energy density. Hence, it is possible to enhance energy density by other sources such as oil or fat. However, dietary fats are antimicrobial and interfere with normal function of the luminal microbes and result in fiber digestion depression. Fat is rapidly hydrolyzed in the rumen and the resultant long chain fatty acids are absorbed onto the fiber, which decreases its accessibility to microbial attack (Leng, 1987) or have a direct toxic effect on the luminal microorganisms, and hence reduce fiber digestibility. Depression of fiber digestion is most severe for fat sources which are high in unsaturated fatty acids than in saturated fatty acids (Jenkins, 1993).

Normally, fat content of ruminant diets is low (< 50 g/kg) and if it is increased above 100 g/kg the activities of rumen microbes are reduced (McDonald et al., 2002). Looper (2001); Palmquist and Conrad (1978) suggested a limit of total fat from 6 to 7% in dry matter. While, Chantaprasarn (2005) indicated that feeding fats to lactating dairy cows by using sunflower oil 2.5% in the concentrate with cassava hay could be a way to meet the energy and nutrient requirements to improve rumen ecology as well as milk yield and quality. Wanapat et al. (2005) stated that supplementation of coconut oil could improve rumen fermentation in terms of the fermentation-end-products.

In contrast, coconut oil can be utilized as a dietary fat supplement to eliminate protozoal population, its potential to improve DM intake, digestibility and animal growth performance. In addition, reduction of the protozoal population increased fungal zoospores and bacteria (Leng, 1982; 1989); (Preston and Leng, 1987). Nguyen Thi Hong Nhan et al. (2001; 2005a); Mom Seng et al. (2001) showed that oil eliminated protozoa from the rumen and cattle grew faster. Nguyen Thi Hong Nhan et al. (2005b) emphasized that drenching of soy bean oil at the rate of 6 ml/kg live weight at the start of the trial improved feed intake, growth rate in cattle and economic profitability.

Feed intake and digestibility of swamp buffaloes

Ruminants are adapted to utilize 'bullky' foods, such as hay and straw. Rice straw and maize stover are roughages with a low nutrient content and low digestibility, which are usually fed to buffaloes as a main diet during the dry season in many Asian countries (Thu, 2001). Therefore ruminants have evolved a special system of digestion that involves microbial fermentation of feed prior to its exposure to their own digestive enzymes. The success of wild ruminants can be largely explained by their ability to digest fibrous plant materials (Hungate, 1966). Ruminants themselves do not produce fiber-degrading enzymes, but they harbor bacteria, fungi, and protozoa that can. The host provides the microorganisms with a suitable habitat for growth, and the microbes supply the animal with protein, vitamins, and short-chain organic acids. Microbial protein accounts for as much as 90% of the amino acids reaching the small intestine, and energy from short-chain organic acids (primarily acetic, propionic, and butyric acids). Ruminal microorganisms can also ferment starch and sugars, and these nonfibrous materials increase fermentation rate and animal productivity (Nocek and Russell, 1988). The rumination and fermentation are relatively slow processes, and fibrous feeds have to stay in the digestive tract for along time until digestible components are extracted. It is long recognized that there is a positive relationship between the digestibility of feed and intake in ruminants; total intake increases when digestibility is high, but intake is actually more closely related to the rate of digestion of diets than to digestibility; although the two last measures are generally related to one another. In other words, feed that are rapidly digested, and have a high digestibility, promote high intake. The faster the rate of digestion, the more rapidly is the digestive tract emptied, and the more space is made available for the next meal. The primary chemical component of feeds that determines their rate of digestion is neutral-detergent fibrous (NDF), which is itself a measure of cell-wall content, the physical form of cell walls also effect intake. The mechanical grinding of roughages partially destroys the structural organization of cell walls, thereby accelerating their breakdown in the rumen and increasing feed intake.

However, nutrient deficiencies that reduce the activities of rumen microorganisms are liable to reduce feed intake. The most common are proteins and nitrogen deficiency, which can correct by supplementation with rumen-degradable protein or with simple source of nitrogen such as urea. The effects of ammonia availability through digestibility and straw intake of cattle; there are two critical ammonia levels. These are 80-100 mg N/l for optimum fibrolytic activity and 150-250 mg N/l for optimum microbial activity (McDonald et al., 2002). In the present study with animals fed on low quality rice straw there were significant improvements of DM, OM and NDF diet digestibility for the supplemented diets compared to the non-supplemented diet. Murphy (1990) reported that increases in nitrogen supply or sparing effects of the branched amino acids led to an increase in the numbers of cellulolytic bacteria and fiber digestion. This agrees with Yuangklang et al. (2001), who found that DM intake and digestibility coefficients were higher for urea-treated rice straw and for cassava hay than for rice straw and ruzi grass hay. Supplements of undegradable protein may also increase the intake of low-protein forages. Other nutrient deficiencies that are liable to restrict feed intake in ruminants are sulphur, phosphorus, sodium and cobalt.

Animal factors affect the intake in ruminants, and if capacity of the rumen is a critical factor in determining the feed intake of ruminants, then circumstances that change the relationship between the size of the rumen and the size of the whole animal are likely to affect intake. Thus, any variations between cattle and buffalo in the proportions and numbers of ruminal bacteria, protozoa and fungi might contribute to the explanation of differences in digestive capability due to fermentation end-products available for absorption and utilization by ruminants (Wanapat, 2001b). When cattle and buffalo are kept under similar conditions, buffalo utilize feed more efficiently with a digestibility of the feeds being typically 2-3 percentage units higher (Wanapat, 1989; Wanapat et al., 1994; Kennedy and Hogan, 1994). Nitrogen utilization in swamp buffalo was found more efficient than that in Malaysian cattle (Devendra, 1985). The feed intake of ruminants follows approximately the proportionality to metabolic bodyweight (W^0.75). In pregnant animals, the increased need for nutrients for foetal development also causes intake to rise. The increased intake in ruminants with the onset of lactation is well known. There is a noticeable lag in the response of food intake to the increased energy demand of lactation. The stress effect is important, namely low environmental temperatures increase intake and high temperatures decrease intake; similarly Leng (1990) reported that the poor condition of cattle in the tropics is more likely to be the result of inefficient digestion in the rumen and inefficient utilization of the nutrients absorbed. In hot environments the heat generated by such inefficiencies is hypothesized to low overall feed intake, which is then expressed as a frank energy deficiency.

Rumen ecology of swamp buffaloes

Rumen ecology plays an important role in fermentation process and in providing end-products to ruminants. The stomach of a ruminant is divided into four compartments: these are rumen, reticulum, omasum and abomasum. In an adult, the reticulo-rumen comprises 85% of the total capacity of the stomach; it provides a continuous culture system for anaerobic bacteria, protozoal and fungi. The digestive tract of ruminants is ideally suited for fermentation (Hungate, 1966). The rumen is a large chamber, the selective retention of large feed particles by the omasum increases the residence time of fibrous feed materials. When large feed particles are ruminated, the surface area and fermentation rate are both increased. Rumination also triggers saliva flow, which maintains the optimal of pH to the microbes and the animal. The optimal pH of rumen for fiber digestion ranges from 6.5 to 7.0 according to Wanapat (2001b). Kopecny and Wallace (1982) reported that muscular contractions mix fresh feed with microorganisms and wash the epithelium with fermentation fluids so the microbial short-chain organic acids can be absorbed. Feed and water enter the rumen and feed is partially fermented to yield principally of volatile fatty acids, microbial cells and the gases methane and carbon dioxide. The gases are lost by eructation and the volatile fatty acids are mainly absorbed through the rumen wall. Microbial cells, together with undegraded feed component, pass to the abomasums and small intestine; there they are digested by enzyme secreted by the host animal, and the products of digestion are absorbed. In the large intestine is a second phase of microbial digestion in the intestine. The volatile fatty acids products are absorbed, but microbial cells are excreted with undigested food components in the faeces.

According to McDonald et al. (2002) the bacteria number is 10⁹-10¹⁰ per ml of rumen content. Over 200 species have been identified, and most are non-spore-forming anaerobes. Microorganisms are an important feature of rumen fermentation. A further point is that the activities of given species of bacteria may vary from one strain to another species. The total number of bacteria and the relative population of individual species vary with diet of the animal; for example, diets rich in concentrate promote high total counts and encourage the proliferation of lactobacilli.

Protozoa are present in much smaller numbers (10⁶ per ml) than bacteria but, they are larger and may equal the latter in total mass. Over 100 species have been identified in the rumen. In adult animals, most of the protozoa are ciliates belonging to two families; the Isotrichidae and the Ophryoscolecidae or Oligotrichs. The large protozoa consume smaller ones, significant numbers of ruminal bacteria can be consumed by protozoa, resulting in an inverse relationship between protozoal and bacterial densities (Williams and Coleman, 1992). Ruminal protozoa are not essential to their host's nutritional status. Nevertheless, many protozoa take up and store small starch granules, thereby modulating the fermentation rate and protecting the animal from acidosis. However, bacterial predation and protozoal lysis can deprive the animal of microbial protein and increase the excess of ruminal ammonia. Some protozoa appear to digest cellulose; up to one-third of fiber digestion can be protozoal (Williams and Coleman, 1997).

According to McDonald et al. (2002) the fungi of the rumen have been studied for less than 30 years, and their place in the rumen ecosystem still has to be fully characterized. They are strictly anaerobic, and their life cycle includes a motile phase (as a zoospore) and a vegetative phase (sporangium). During the later phase they attach to feed particles by rhizoids, which can penetrate cell walls. At least 12 species or strains have been identified, typically those belonging to the genus Neocallimastix. The rumen fungi are capable of utilizing most polysaccharides and many soluble sugars; some carbohydrates not used by these fungi are pectin, polygalacturonic acid, arabinose, fucose, mannose and galactose. The contribution of rumen fungi to fermentation of feed has not yet been quantified, but it is known that they constitute 10 per cent of the microbial biomass when diets are rich in fiber. The rumen microorganisms can be envisaged as operating together, as so called consortia, to attack and break down feeds. Some, like the fungi, are capable of invading and colonizing plant tissues; others follow up to ferment the spoils of the invasion

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