Comparison of cassava hay yield and chemical composition of local and introduced varieties and effects of levels of cassava hay supplementation in native beef cattle fed on rice straw
 

Phanthavong Vongsamphanh and Metha Wanapat^*

Livestock Research Center, National Agriculture and Forestry Research Institute,
Ministry of Agriculture and Forestry, Vientiane, Lao PDR
phanthavongkv@hotmail.com
^*Department of Animal Science, Faculty of Agriculture
Khon Kaen University, Khon Kaen 40002,Thailand
metha@kku.ac.th

Abstract

In the first experiment, a local and an introduced cassava varieties were studied to compare yield and chemical composition using a 2x2 factorial arrangement in a randomized complete block design with 4 replications. The aims were to determine the effects of different initial and subsequent cuttings on yields and chemical composition of local and an introduced variety (Rayong72; RY72) from Thailand.

Dry matter (DM) and protein yields of cassava variety RY72 at each harvest were higher than the local variety. The CP percentages of the foliage (DM basis) were from 22.6 to 25.8% in RY 72 and 17.2 to 25% in the local variety. NDF was 54.2 to 58.8 % and 53.2 to 55.7 %, ADF 26.2 to 30.5 % and 24.7 to 34.2 %, and ADL 9.4 to 11.6 % and 11.3 to 11.8 %, in RY 72 and local variety, respectively. Condensed tannin (CT) was 3.3 to 3.4 and 3.5 to 3.8 %, in RY72 and local variety, respectively. In the second experiment, the effect of level of cassava hay (CH) supplementation on rumen parameters, digestibility and rice straw intake in growing native cattle was studied. Four, 2-year-old rumen fistulated bulls were randomly assigned to a 4 x 4 Latin square design to receive four dietary treatments; RS = rice straw (Control), RSCH2 = RS + 200 g CH/head/d, RSCH4 = RS + 400 g CH/head/d, RSCH6 = RS + 600 g CH/head/d. All animals were dewormed and injected with vitamin A, D₃ and E prior to commencement of experimentation. Each feeding period consisted of 14 days for rice straw intake measurement and was followed by a 7 days collection period of feed, rumen fluid, blood and fecal samples. Rice straw and CH contained in DM: 5.3 and 27.3% CP and (for CH) 3.6% condensed-tannins. of cattle were improved with CH supplementation. Intakes of rice straw and weight changes were enhanced by CH supplementation.   Ruminal NH₃-N and blood urea nitrogen were increased as CH level increased. Bacterial and fungal zoospore populations were  increased while protozoal population was decreased as a result of CH supplementation. Digestion coefficients particularly those of DM, OM, and CP were increased by CH supplementation.

It is concluded that CH supplementation improves intake of rice straw, rumen ecology, and digestibility in native cattle.

Key words: Cassava foliage, variety, rice straw, rumen ecology, cattle, digestibility, intake.

Introduction

Native beef cattle are the most important bovine animals on small farms in Lao PDR. The importance of cattle can not be judged only by their economic contribution from meat, since social, culture and other values such as draught power, transportation and manure are even more important at village level. However, farmers have experienced frequent animal losses through diseases due to very basic causes such as a shortage of feeds both in quantity and quality and this situation is still continuing. However, due to the enormous amount of crop-residues locally available, there is potential for their use as feed, especially for ruminants (Leng et al 1993). Wanapat (1999) reported that use of straw in animal feeding is limited by its low nutrient value due to the strong physical and chemical bonds between carbohydrates and indigestible lignin. 

Cassava or tapioca (Manihot esculenta, Crantz) is grown widely in tropical countries. This plant is well known for its adaptability to poor soil condition, drought resistance and pest tolerance. Usually, cassava is grown for root production and is regarded as a cash crop. However, attention has recently been focused on the potential of the whole cassava crop in livestock production (Preston 2002; Wanapat 2002). Select a variety available in the location, which has shown to produce the most abundant leaf and highest leaf to stem ratio. If not available, any local varieties can be used. Sweet variety could be better since it contain remarkable less hydro-cyanic acid (HCN) than bitter variety, however, sun-drying will help to eliminate HCN more than 90%. Recently, Wanapat et al. (1997) has paid attention on cassava hay, which combined leaves, stems and petiole of cassava plant for feeding to ruminants. The results revealed that cassava hay could be good quality roughage for ruminant production. However, the new approach, on addition, was to cultivate cassava for leaf / hay production by harvesting at early growth stage of 3 months and every two month thereafter to produce higher collective DM yield and higher crude protein and other important nutrients. Digestibility and intake studies in cattle resulted in relatively high values, which demonstrated that cassava hay was palatable and digestible. More recent work has been reported that cassava hay was a good source of plant protein for ruminants because rumen protein degradability was relatively low with could provide a higher content of rumen by-pass protein. The use of CH in ruminants particularly in dairy cattle has been successfully implemented in several ways such as on-top supplementation (Wanapat et al., 2000a, 2000b), inclusion in concentrate diet (Bezkorowajnyi et al.,1986, Wanapat et al., 1992), inclusion in high quality feed block (Koakhunthod et al., 2001).

However, the use of CH for animal feeding in Laos has been negligible. It was therefore the objective of this experiment to investigate the cassava production and use of CH in various levels of supplementation in native beef cattle fed on rice straw.

2. Materials and methods

Experiment 1; Comparison of cassava hay yield and chemical composition of local and introduced varieties.

Site of experiment

The experiment was carried out during May 20, 2002 to December 20,2002 on sandy loam soil. The pH of the soil was about 4-5.

Land preparation and cassava planting

Soil was ploughed well to break soil clusters and to eradicate weeds by using small tractor. At initial time, fertilizer was applied at 150 kg/ha (N-P-K, 15-15-15). Each plot (4x8m) was prepared to grow cassava (4 plots for each variety). Spacings of 90x60 cm between row and plant were used. Cassava stalk of RY72 (from Thailand) and local varieties were cut (15cm) and embedded in prepared soil making about 60ºC angle to the soil. After about 10 days, all planting stalks started to produce young leaves.

Harvesting and determination of yield and chemical compositions

The initial cutting at 3 months was made on August 20,2002 and followed by second cutting at every 2 months. Approximately at 9.00 a.m. of the sampling day (when cassava leaves are free from fog), 4 samples were randomly collected from 4 sites by hand breaking of the stem about 20-30 cm above the ground (with 3-5 remaining branches) and weighed separately and recorded for fresh yield and sampling for dry matter determination.

DM, ash, CP were measured using procedures of AOAC (1990), NDF, ADF, ADL (Goering and Van Soest, 1970). Condensed tannins (CT) in cassava hay was estimated by Vanillin-HCL method (Burns, 1971 modified by Wanapat and Poungchompu, 2001).

Statistical analysis

All collected data from the experiment was subjected to analysis of variance using General Linear Model Procedure of SAS (1998) according to a 2x2 Factorial arrangement in Randomized Complete Block Design. (RCBD). Treatment means were compared by Duncan's New Multiple Range Test (Steel and Torrie, 1980).

Experiment 2; Effects of levels of cassava hay (CH) supplementation in native beef cattle fed on rice straw.

Location

The experiment was carried out at the experimental farm of Namsuang Livestock Research Center, 40 km from Vientiane city (May to September, 2002).

Animals

Four native bulls, about 2 years old with 150 kg average live weight, were fitted with permanent rumen fistulae. Vaccination program, deworming and vitamin A, D₃, E injections were given before the commencement of the experiment. Each animal was weighed at the beginning and the end of each period.

Housing

The animals were placed in individual pens with permanent roof. Clean, fresh water were available all times during the whole experiment, cleaning of the pen was done daily.

Experimental and statistical design

The animals were randomly assigned to receive respective dietary treatments according to a 4x4 Latin square design and treatments are as follows:

Treatments (T)

T₁: control (0 g of CH)

T₂: supplemented with 200 g /hd/d of CH

T₃: supplemented with 400 g /hd/d of CH

T₄: supplemented with 600 g /hd/d of CH

Experimental lay-out:

	Animals
Periods	Cattle 1	Cattle 2	Cattle 3	Cattle 4
Period 1	T1	T4	T3	T2
Period 2	T4	T2	T1	T3
Period 3	T2	T3	T4	T1
Period 4	T3	T1	T2	T4

Model: Y_ijk = µ + R_i + C_j + T_k + E_ijk

where Y_ijk = Observed value from row i column j treatment k

µ = Overall sample mean

R_i = Effect of row i

C_j = Effect of column j

T_k = Effect of treatment k

E_ijk = Experimental errors of the mean

Management and feeding

Rice straw (RS) were collected from the local farmers and transported to store for feeding at the station and was given on ad lib basis and weighed every day to measure intake.

Cassava hay (CH) was preparation after planting 3 months; hole cassava plant was harvested by hand with the cutting height about 10cm above the ground. The foliage was chopped into small pieces with the size of 2-3 cm by chopping machine. After that it was sun-dried from 2-4 days until the leaves are crispy dried to reduce moisture content > 85% DM and hydro-cyanic acid (HCN). CH was stored and fed to the cattle offered according to the respective treatments in two equal parts in the morning and in the afternoon during experimentation.

All animals were given 200 g/hd/d of mixed feed, which rice bran and 5% of urea (rice bran 190 g: urea 10 g).

Feed intake of each animal was recorded daily by weighing the given and refusal feed

Feed intake (kg)= Given (kg)-Refusal (kg)

Measurements and Chemical Analyses

For each period, there were consist of two feeding periods, the adjusting period and actual intake and sample collection period. All animals were adjusted to feeds for one week before they receive their respective feeds for three weeks. During this feeding period, rice straw intakes were measured. During the last two days of each period, rumen fluid were collected at 0, 2, and 4 h-post feeding. Rumen pH was measured immediately using field pH meter. Rumen fluid was prepared for later analysis of NH₃-N using KJELTEC AUTO 1030 analyzer (Bromner and Kennelly, 1965) and volatile fatty acids (VFAs) using HPLC model water 600; UV Detector (Millipore corp.) (Samuel et al., 1997). Blood was collected from jugular vein from each caw at 0, 2, and 4 h-post feeding and was analyzed for blood urea nitrogen (BUN) by method of Crocker (1967). Feeds were randomly collected and fecal samples were collected from rectum during the last 5 days for each period and composited for later chemical analyses. Feeds and fecal samples were analyzed for DM, ash, CP using procedures of AOAC (1990), NDF, ADF, ADL (Goering and Van Soest , 1970). Acid insoluble ash (AIA) was determined by Van Keulen and Young (1977). AIA was used to calculate for DM, OM, CP, NDF, ADF, ADL digestibilities. Condensed tannins (CT) were estimated by Vanillin-HCL method (Burns, 1971 modified by Wanapat and Poungchompu. 2001).

Sample chemical analyses were carried out at the Ruminant Nutritional Laboratory of Department of Animal Sciences, KhonKaen University, Thailand.

Statistical analysis

Analysis of Variance (ANOVA) was analyzed using Proc. General Linear Model (GLM)(SAS, 1998) and treatment means be compared by Duncan's New Multiple Range Test (Steel and Torrie, 1980).

3.Results and Discussions

Exp I; Comparison of cassava hay yield and chemical composition of local and introduced varieties.

Fresh matter, dry matter and protein yield of whole cassava crop

The data of fresh, dry matter (DM) and protein yield of cassava at initial cutting at 3 months and subsequent cutting every 2 months are presented in Table 1. The fresh, dry matter, and protein yields for RY72 and local verities were 35.1, 15.2, 7.7, and 3.5, 1.9, 0.8 ton/ha, respectively.

As obtained, the yield of RY 72 was significantly (P<0.01) different of fresh, DM and protein yield The DM yield was relatively higher than those reported by Wanapat et al., (1997) for cassava grown in Thailand and Vietnam. However, the different value may be depended on cultivar, age of plant, plant density, soil fertility and climate (Gomez and Valdivieso, 1984; Wanapat et al., 2000a).

Chemical composition of cassava foliage

The chemical analysis of cassava foliage (CF) of RY72 and local varieties are given in Table 2. the CP percentages were from 22.6 to 25.8 in RY 72 variety while 17.2 to 25 in local Variety. The CF of RY72 variety has been similar DM, NDF, ADF, ADL, CP, OM, Ash, Ca, P and condense tannins (CT). as previously reported by Wanapat, (2003). Furthermore, Moore and Cock (1985) reported that CP in cassava whole plant was 25.5%. Other studies Poungchompu et al. (2001) has shown CP value in range from 20.6 to 22.0 %. However, in this study was found that in local variety was lower CP content than RY 72 variety. Protein content in leave ranges from 16.7 to 39.9 % but it varies to variety, stage of maturity, soil fertility and climate (Ravindran, 1993; Wanapat et al., 1997).The nutritive value of CF may depend on cultivate, age of plan, plant density, soil fertility, harvesting frequency and climate (Gomez and Valdivieso, 1984; Wanapat et al., 1997). Lower protein content of local variety than RY 72 could be due to difference variety. Fiber components of cassava foliage in RY 72 and local variety, NDF were 54.2 to 58.8 % and 53.2 to 55.7 % respectively, ADF were 26.2 to 30.5 % and 24.7 to 34.2 % receptively, ADL were 9.4 to 11.6 % and 11.3 to 11.8 % .The values of NDF, ADF and ADL in the present study for both varieties were similar to those were reported by Wanapat, (2003) at 42.7 to 56.0; 25.9 to 38.0 and 10.4 to 13.6 % respectively. Fiber components of cassava foliage in local variety were slightly higher than RY 72 variety. The differences amount of NDF and ADL in whole plants could be effect from difference in age of plant, especially NDF and ADF in stems and indicating the formation of tannin-fire complexes that were not solubilized in the acid detergent solution (Getachew et al., 2001). In this study, condensed tannin (CT) in RY 72 and local variety were 3.3 to 3.4 and 3.5 to 3.8 % respectively. It was slightly lower as compared to from 3.8 to 4.2 by Poungchompu et al. (2001). Higher condense tannin was found in local variety than those in RY 72. Barry and McNabb, (1999) reported that concentration of condensed tannin was strongly different among genotypes.

Exp. II; Effects of levels of cassava hay (CH) supplementation in native beef cattle fed on rice straw.

Chemical composition of diet

Feed ingredients and chemical composition are presented in table 3 Rice straw (RS) contained 5.3% CP, 89.4% NDF, 52.6% ADF and 10.3%ADL, while cassava hay (CH) consisted of 27.3 % CP, 67.7% NDF, 41.4% ADF, 13.2% ADL and 3.6% CT (condensed tannins), respectively.

RS was collected on second cropping in August and had higher CP, fiber and lignin fractions. Generally, straw in animal feeding is limited by its low nutrient value due to the strong physical and chemical bonds between carbohydrates and indigestible lignin. The lignin not only acts as diluents in the feed ration, but also represents a barrier, which protects the cellulose from microbial breakdown. Besides the lignified feeds was also low digestibility (15-44%), low crude protein content (1.5-6%), poor palatability and bulky. It is therefore to supplement in rice straw based diet in order to enhance its utilization.

The level of CP in CH was slightly higher than the standard mean value of 23.5%, as reported by Wanapat et al. (2003). Furthermore, Moore and Cock (1985) reported that CP in cassava whole plant was 25.5%. It was reported earlier that CP value in CH was 24.9% (Wanapat et al., 1997) and from 20.6 to 22.0% (Poungchompu et al., 2001) However the NDF, ADF and CT were in accordance with the previously reported values for CH. The slightly higher CP level may be caused by the time of harvesting, about 3 months after planting and the soil fertility. Nguyen et al. (2002) reported that the time of harvesting after planting affected chemical composition of CH and was found that the CP level decreased; while the fiber, lignin and CT fraction increased with early harvest after planting. The optimum quality of CH was obtained by harvesting 3 months after planting and at every 2 months continuously.

In addition, condensed tannin (CT) in CH was measured to be 3.6 % of DM (table 3). Result was found closer as compared to Poungchompu et al., (2001). who found range of CT was 3.8 to 4.2% in CH. this range of CT has been reported to be beneficial to ruminants, in terms of increased rumen by-pass protein, decreasing number of parasites and enhanced rumen fermentation (Kahn and Diaz-Hernandez 2000; Makkar, 2000; Wanapat et al., 2000a; Wanapat et al., 2000b). These findings imply that both harvesting time and season affected chemical composition. Wanapat et al. (2003) agreed by explaining that CH harvested at younger stage of growth (3 months) not only contained protein up to 25% CP and with a good profile of amino acids while CT were generally found lower.

The effect of cassava hay supplementation on live-weight change, DM intake, digestibility in native beef cattle

As shown in table 4, weight changes of cattle were not affected (p>0.05) by CH supplementation, but tended to linearly increase with increasing level of CH supplementation. As average day gain (ADG) of each period (21 days) were -0.05, -0.03, 0.08 and 0.11g per head per day for T1, T2, T3 and T4, respectively. The result shows that improved weight gain were obtained at 400, 600 g CH/head/d supplementation. This results were in accordance with the work conducted in the Dominican Republic that fresh cassava leaves as the only source of forage in a diet of molasses-urea, can support good growth rates (>800 g/day) in fattening cattle (Ffoulkes et al. 1978; Ffoulkes and Preston 1978; Ffoulkes and Preston 1979). Cassava hay with high level of protein could provide protein to the cattle for maintenance and possibly for growth. In other reports, dried cassava leaves were supplemented to ruminants; digestibility, intake, and average daily gain were improved (Wanapat, 1983; Devendra, 1985; Bezkorowajnyi et al., 1986). Protein requirements for expressed as a ratio of dietary CP to dietary TDN. Stage the amount of protein consumed daily to achieve a target growth rate in growing heifers is the amount of rumen degradable protein (RDP) require for microbial growth given the level of ruminally available carbohydrate (Preston 1982; NRC 2001)

The results of levels of CH supplementation on rice straw intake and total DM intakes in terms of %BW and g/kg W^0.75 are presented in table 4. Enhancing of CH supplementation could significantly (P<0.05) increase the total DM and OM intake without decreasing the intake of RS. and were highest in treatment at 600g/hd/d supplementation. This results were accordance with report by Wanapat et al. (2000a) that feeding CH to dairy cows increased RS intake of dairy cattle. As a consequence, total DM intakes were increased by CH supplementation as compared to control. The difference could be attributed to high digestibility and high rumen by-pass protein since it contained tannin-protein complex. Moreover, medium CT concentrations (30 to 40 g/kg DM) had no effect upon voluntary feed intake (VFI) (Wang et al., 1996) but have reduced protein solubility and degradation in the rumen (Min et al., 2001), increased the absorption essential amino acids (EAA) from the small intestine (Waghorn et al., 1987a; Barry and McNabb, 1999).

Effect of levels of CH supplementation on rumen parameters, ammonium nitrogen (NH₃-N), blood-urea nitrogen (BUN)

Rumen ecology parameters were measured for temperature, pH, NH₃-N and BUN. As shown in Table 5, rumen temperature, pH, NH₃-N and BUN were similar among treatments and values were quite stable at 38-39 °C, pH in range of 6.4-6.6, NH₃-N (11.8-13.9), and BUN (10.2-12.4), respectively. All those values were in normal range as reported as an optimal for microbial digestion of fiber (Hoover, 1986), digestion of protein (Wanapat, 1990). Adhesion to cellulose of the three cellulolytic species was completely inhibited at temperature below 4 °C, and in R. albus and F. succinogenes adhesion also decreased in temperature above 50 °C and achieved maximal values at 30 to 38°C (Gong and Forsberg, 1989; Minato et al., 1993; Morris and Cole,1987; Pell and Schofield, 1993; Roger et al., 1990). Moreover, the rumen processes that ensure maximum feed intake and digestibility, efficiency, normal butterfat test, and healthy cows all operate within a narrow pH range of 6.4 to 6.8. Roger et al. (1990) showed that the adhesion of Fibrobacter succinogenes, to cellulose increased as pH was increased from 4.5-6, remained stable between pH 6 and 7, and fell abruptly above pH 7.5. Notwithstanding, Gong and Forsberg (1989) reported that the adhesion of this bacterium did not change over a pH ranger of 5.3 to 6.8. Roger et al. (1990) also showed that the adhesion of R. flavefaciens to cellulose was stable at pH value between 3.3 and 7.5, and decreased at pH 8, whereas Rasmussen et al. (1989) reported that the adhesion of the bacterium was not affected by changes in pH between 6 and 8. The adhesion of R. albus was not affected by changes in pH between 5.5 and 8 (Morris, 1988).

Moreover, differences in levels of CH supplementation did not significantly affect on ruminal ammonia concentration (P>0.05) but tended to be increased with enhancing levels of CH supplementation. (Table.5). This would indicate that available rumen NH₃-N could be used in microbial protein synthesis. According to numerous reports, optimal level of ruminal ammonia concentration for efficient digestion was from 5.0 to 25.0mg%5 (Preston and Leng (1987). 15-30 mg %, (Perdok and Leng, 1990; Wanapat and Pimpa, 1999). Likewise, Wallace (1979) earlier observed an increase in situ dry matter and CP degradation rates when rumen ammonia concentration increases from 9.7 to 21.4 mg % in rumen fluid. These studies assumed that increase degradation fermentation of rumen substrates was the result of increased rumen microbial activity and growth. However, different substrates required different concentrations of ammonia to achieve optimal microbial yield (Orskov, 1992). Therefore the microorganisms in rumen of cattle supplemented with CH could be more efficient and the digestion could be better. CH supplementation could improve the efficiency of microorganisms in the rumen. This result could be a good explanation for the higher intake and the tendency of increasing body weight in CH supplemented cattle as mentioned before.

The increases in rumen NH₃-N levels also resulted in increasing levels of BUN and the values were linearly increased as levels of CH increased in the diets. BUN has been known as a factor, which highly related to dietary protein. Protein in the form of ammonia or amino acids can be absorbed from to major sites in the ruminant animal, the rumen and the small intestine. Preston et al. (1966) stated the quantity of ammonia absorbed from the rumen was the reflect in circulating BUN and was highly correlated with CP intake by cattle, r²= 0.99. Bunting et al. (1987) reported that BUN levels reflecting protein status of cattle and corresponding positively to change in ammonia concentration in rumen fluid. Song and Kennelly (1989) reported that increasing ruminal ammonia nitrogen from 11.2mg% (in control) to 16.3, 24.8 and 34.9mg% by infusion of NH4HCO3 led to increase BUN linearly. BUN was also increased linearly with the results and was closely correlated to degradable protein fraction in the diet. However, DePeters and Ferguson (1992) noted that urea concentration in blood was determined more by protein catabolism than by ammonia concentration in the rumen. The trend of increasing BUN in the present study might be due to the increase in rumen NH3-N and absorbable protein from the small intestine. Moreover, BUN was also depending on P/E balance. Diets, which balance in P/E, BUN concentrations, were 12.7mg%. BUN lowers than this reference could be due to the insufficiency in CP per unit of energy (Hwang et al., 2001). BUN values in the current study particularly in the control were lower as compared to the mentioned reference. This result could be interpreted that the current feeding regime was low in term of P/E balance. Typically BUN concentrations peak about 4 to 6 h-post feeding. Likewise, Huntington et al. (2001) reported that rumen ammonia concentration increases with increasing dietary CP intake, but decreases with increasing rumen upgradeable protein (RUP) as a percent of dietary CP. BUN concentrations followed similar trends as rumen ammonia. Hutjens and Jordon (1994) stated that if BUN concentrations drop below 10 mg%, a shortage of protein may be occurring. However, the slightly higher BUN of the supplemented native cattle in this research indicated that CH enhanced protein nutrition.

The effect of CH supplementation on the microbial ecology in the rumen fluid

Effect of rumen microorganisms, total counts of bacteria, protozoa and fungal zoospores were measured at 0, 2, and 4 h-post feeding, and are presented in Table 6. Total bacteria counts were significantly different at 2 and 4 h-post feeding. As shown, CH supplementation was linearly increased (P<0.05) with increasing supplementation level in bacterial and fungal zoospores population than the control, respectively. Total bacteria count was highest in T2, fungal zoospores were significant but no differences T2, T3, and T4. Meanwhile, protozoal population were found slightly decreased as levels of CH supplemented increased, 5.0 to 3.7x10⁵ cell/ml, in control and treatment with CH supplementation, respectively. It appeared that CH supplementation in cattle fed rice straw might play an important role in changing rumen microorganism populations. It is possible that CP level and CT presented in CH may play importance role. As previously reported by Makkar et al. (1995); McSweeney et al. (1999) that condensed tannins improved rumen ecology especially enhancing microbial protein synthesis, however, mode of action needs to be substantiated. Apparently, enhanced levels of CH supplementation tended to decrease the number of protozoa, may explain the increase in fungal zoospore per ml rumen fluid. As removal of protozoa has been associated with an increase in the concentration of fungal zoospore (Leng, 1982). In addition, in the present study CH supplementation could maintain an optimal ruminal pH and increased the level of NH₃-N closer to 15 mg%. These factors may have contributed to enhanced bacterial growth. Song and Kennelly (1990) found that total mixed bacteria tended to increase with increasing level of NH₃-N in the rumen fluid of cattle. Dietary protein breakdown or protease activity is accomplished by a number of rumen microorganism and in a series of steps with each step involving different rumen microorganism. Argyle and Baldwin (1989) showed that growth of ruminal bacteria was greatly stimulated by the addition of dietary peptides and amino acid.

The effect of cassava hay supplementation on feed intake, digestion coefficients, digestible nutrient intake and estimated metabolizable energy (ME) intake in cattle

Table 7 shows data on intake and digestibility of nutrients. Intakes in terms of % BW and g/kg W^.75/d were significantly enhanced by CH supplementation are found (P<0.05) and were T1<T2<T3<T4 ,respectively. Digestion coefficients of DM, OM, CP, NDF and ADF were also found significantly increased (P<0.05) which ranging from highest to lowest were T4>T3>T2>T1 respectively, As a result, digestible DM, OM and CP intakes as well as estimated energy intake (Mcal ME/d, ME kg/kg DM) were significantly different (P<0.05) T4>T3>T2>T1, respectively, Higher level of CP in CH may attribute to the higher values.

As a result, coefficient digestibilities were highest in 600g of CH supplementation group. These data were in agreement with those reported by Wanapat et al. (1997, 2000a). CH had a high DM digestibility (71%) and high ruminal by pass protein since it contained tannin-protein complex. Moreover, CT concentrations (30-40 %) had no effect upon voluntary feed intake (VFI) (Terrill et al., 1992b; Wang et al., 1996) but have reduced protein solubility and degradation in the rumen (Min et al., 2001) increased the absorption essential amino acid (EAA) from small intestine (Waghorn et al.,1987a; Barry and McNabb, 1999).

In this study, CT in CH was present at 36 g/kg DM. It may have led to increased absorption of EAA from the small intestine and increased animal productivity without effecting VFI, thus improving the efficiency of food conversion. However, ADF showed a trend to be higher but was not significantly different. It is possible that the high fibrous fraction (ADL) could have attributed to lower digestibility (Hart and Wanapat, 1992; Wanapat et al., 1997, 2000a), especially the large proportion of lignified cell walls with low fermentation rate and digestibility, leading to low rate of disappearance through digestion or passage and limited feed intake. There is a negative relationship between cell wall constituents (CWS) and voluntary intake (Van Soest,1965; Osbourn et al., 1974). Mertens and Loften (1980) concluded that changes in the composition of cell wall involving lignin and possibly silica limited the potential extent of digestion whereas the rate of digestion is limited by the chemical entities other than by crystalline or physical nature of fiber. Wanapat et al. (1997) found that ruminal DM degradability of all parts of CH increased as time progressed to 72 hours. Highest DM was shown for leaf, whole crop and stem (78.7, 68.2 and 61.7%, respectively). These high degradability support increased nutrient intake as shown in this research. This result agreed with work of Preston and Leng (1987), in animals fed low nitrogen diets, supplementation with by pass protein stimulates feed intake. Likewise, Clark et al. (1992) further explained that when rumen ammonia concentrations were grater than 5 mg/dl in rumen fluid, passage of microbial protein synthesis may be more highly correlated with organic matter intake. Intake of metabolizable energy (ME) was significantly (P<0.05) enhanced in CH supplemented cattle as compared to control. CH could significantly increased intake and digestibility as shown in table 7. The high DM degradation of whole crop CH (Wanapat et al., 1997) may explain the increased ME intake in cattle.

4. Conclusions and Recommendations

Under these current experiments, the following conclusions and recommendations could be made:

= Cassava cultivation to produce cassava hay could be practiced under Lao condition.

= Cassava hay (CH) harvested at 3 months and followed by 2 months resulted in higher DM and protein yields in RY72 than in local variety.

= Cassava hay supplementation for native cattle can improve rumen ecology by maintaining normal pH, temperature, increasing bacterial and fungal zoospore population and decreasing protozoal population particularly at 600 g/hd/d.

= Cassava hay supplementation increased intake, digestibility and ME of feed

especially when fed with rice straw diet.

= Cassava hay should be recommended to be used as a protein source especially during the dry season.

= Furthermore, on-station research on CH and energy levels (cassava chips)

and on-farm research should be conducted in relation to its supplementation effect and farmers' perspectives and adoptions.

5. Acknowledgements

The senior author wishes to extend warmest gratitude to all who have supported the research and development work on this study particularly Swedish International Development Agency (SIDA) and Swedish Agency for Research Cooperation with Developing Countries (SAREC) for financial support; National Agriculture and Forestry Research Institute (NAFRI); Livestock Research Center (LRC) and Ruminant Nutritional Laboratory of Department of Animal Science, Khon Kaen University, Thailand. for providing facilities and animals for conducting experimental work and chemical analyses of samples.

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Table 1:A comparison of fresh, dry matter and protein yield of cassava varieties Rayong72 and Lao local (ton/ha)

Fresh yield Dry Matter yield Protein yield

First cutting

Rayong72 18.2 a 4.0 ^a 1.0 ^a

Lao local 9.6 ^b 2.2 ^b 0.6 ^b

Significance ** ** **

CV, (%) 13.9 14.1 13.5

Second cutting

Rayong72 11.9 ^a 2.4 ^a 0.5 ^a

Lao local 4.3 ^b 0.9 ^b 0.2 ^b

Significance ** ** **

CV, (%) 17.9 18.2 17.3

Third cutting

Rayong72 4.9 ^a 1.3 ^a 0.3 ^a

Lao local 1.3 ^b 0.3 ^b 0.08 ^b

Significance ** ** **

CV, (%) 27.1 27.2 28.4

Total cutting

Rayong72 35.1 ^a 7.7 ^a 1.9 ^a

Lao local 15.2 ^b 3.5 ^b 0.8 ^b

Significance ** ** **

CV, (%) 16.3 16.6 16.0

Table 2:Effects of different cutting on chemical composition of cassava foliage

Rayong72 Local First Second Third First Second Third

DM, % 92.5 94.4 93.6 91.9 94.7 91.6

% DM

NDF 54.2 58.8 54.5 57.1 55.7 53.2

ADF 30.5 31.0 26.2 34.2 33.5 24.7

ADL 10.3 9.4 11.6 11.8 11.3 11.8

CP 25.8 22.6 25.7 23.0 17.2 25.0

OM 92.7 94.9 92.4 93.4 95.1 94.9

Ash 7.2 5.2 7.5 6.5 4.9 5.0

Ca 1.2 0.74 1.26 0.8 0.72 0.8

P 0.39 0.29 0.25 0.32 0.29 0.25

Condensed tannin 3.4 3.3 3.3 3.8 3.6 3.5

DM=dry matter, NDF=neutral detergent fiber, ADF=acid detergent fiber, ADL=acid detergent lignin, CP=crude protein, OM=organic matter,

Table 3. Chemical composition of cassava hay (CH), untreated rice straw

(UTRS), and mixed feed (DM basis)^a ____________________________________________________________

Items DM Ash OM CP NDF ADF ADL CT AIA

% DM

Cassava hay (CH) 93.7 8.0 91.9 27.3 67.7 41.7 13.2 3.6 1.3

Rice straw (RS) 94.7 12.7 87.2 5.3 89.4 52.6 10.3 0 7.5

Mixed feeds ^b 90.8 12.8 87.2 34.4 63.1 42.9 6.7 0 9.1

________________________________________________________________

^aDM = dry matter, Mixed feeds ^b = Rice bran+Urea, CP = crude protein,

OM = organic matter, NDF = neutral-detergent fiber, ADF = acid-detergent fiber, ADL = acid-detergent lignin, CT = condensed tannins.

Table 4. Effect of various levels of cassava hay on weight change, rice straw, cassava hay and total dry matter intake.

Item	Level of cassava hay supplementation, g air-dried/hd/d					SEM
	0	200	400		600
Initial weight, kg 153.0 153.5 151.0 150.0 1.55 Final weight, kg 150.8 151.1 153.4 154.2 1.28 ADG, g/hd/21 days/period -0.05 -0.03 0.08 0.11 0.06 Rice straw DM intake/hd/d
kg	3.3 a	3.4 a b		3.4 a b	3.5 b	0.04
%BW	2.17 a	2.20 a b		2.26 b c	2.33 c	0.02
G/kgW0.75	76.3 a	77.6 a b		79.3 b	81.6 c	0.64
Total DM intake/hd /d* kg	3.5 a	3.7 b		3.9 c	4.1d	0.35
%BW	2.3 a	2.4 b		2.6 c	2.7 d	0.02
g/kgW0.75	79.8 a	84.9 b		90.7 c	97.6 d	0.64

^a,b,c,d values on the same row with different superscripts differ (P<0.05)

DM = dry matter, OM = organic matter; SEM = standard error of the mean

*All cattle received total feeds including mixed feed (rice bran and urea) at 150 g DM/hd/d

Table 5. Effect of various levels of cassava hay on temperature of rumen (^oC), ruminal pH ammonia nitrogen (NH₃-N) and blood urea nitrogen (BUN, mg/dl)

	Level of cassava hay supplementation,g air-dried/hd/d				SEM
	0	200	400	600
Temperature of rumen °C
0 h- post feeding	38.5	38.7	38.2	39.1	0.25
2 4	38.4 38.5	38.4 38.4	38.0 38.7	38.2 38.7	0.19 0.17
Mean	38.5	38.5	38.3	38.7	0.14
Ruminal pH
0 h- post feeding	6.4	6.6	6.5	6.6	0.05
2 4	6.4 6.4	6.6 6.5	6.6 6.4	6.6 6.5	0.05 0.06
Mean	6.4	6.6	6.5	6.6	0.06
NH3-N, mg/dl
0 h- post feeding 2	10.6 12.2	9.8 13.2	11.3 14.9	12.5 13.8	0.97 1.15
4	13.8	12.5	15.5	14.3	1.33
Mean	12.2	11.8	13.9	13.5	0.97
BUN, mg/dl
0 h- post feeding 2 4	10.6 10.7 12.0	8.6 10.9 11.0	10.0 13.1 14.2	10.7 12.0 13.6	0.86 1.26 1.41
Mean	11.1	10.2	12.4	12.1	1.06

SEM = standard error of the mean

Table 6. Effect of various levels of cassava hay on bacterial, protozoal and fungal zoospore population.

Total count	Level of cassava hay supplementation,g air-dried/hd/d							SEM
	0	200		400		600
Bacteria, x1010cells/ml
0 h- post feeding 2	5.6 5.1a		6.4 8.0 c		5.4 6.2a b		5.5 7.1b c	0.61 0.44
4	5.0a		6.4b		6.7 b		7.0b	0.40
Mean	5.3a		6.9b		6.1a b		6.5a b	0.39
Protozoa, x105cells/ml
0 h- post feeding 2	5.9 4.4		5.3 4.2		4.0 3.8		5.2 2.5	1.07 0.66
4	4.7		4.0		3.6		3.3	0.68
Mean	5.0		4.5		3.8		3.7	0.73
Fungal zoospores, x106cells/ml
0 h- post feeding 2	3.0 a 3.4 a		3.3 a b 4.6 a b		4.0 a b 4.8 a b		4.5 b 5.4 b	0.36 0.47
4	3.4 a		4.3 a b		4.7 a		4.9 b	0.31
Mean	3.3 a		4.0 a b		4.5 b		4.9 b	0.30

^{a , b, c} values on the same row with different superscripts differ (P<0.05)

SEM = standard error of the mean

Table 7. Effect of various levels of cassava hay on feed intake, digestion coefficients and digestible nutrient intake (kg/d).

Items	Level of cassava hay supplementation,g air-dried/hd/d				SEM
	0	200	400	600
DM intake, kg/d Kg	3.5 a	3.7 b	3.9 c	4.1 d	0.35
% of BW	2.3a	2.4 b	2.6 c	2.7 d	0.02
g/kg BW 0.75	79.8 a	84.9 b	90.7 c	97.6 d	0.64
Digestion coefficients %
DM	55.1a	55.8a	56.6a	58.3b	0.44
OM	60.8a	61.4a b	62.0a b	62.9b	0.53
CP	49.2a	51.9b	52.9b	56.5 c	0.47
NDF ADF	60.9a 46.7a	61.2a b 47.0a	61.6a b 47.9b	62.3b 48.1b	0.31 0.26
Digestible nutrient intake, kg/d
DM OM CP	1.97 a 1.86a 0.11a	2.04 b 2.01 b 0.15 b	2.08 b 2.06b 0.17 c	2.20c 2.14b 0.21d	0.02 0.04 0.02
NDF	0.35 a	0.41 a b	0.44 b c	0.50c	0.02
ADF	0.86	0.90	0.91	0.92	0.02
Estimated energy intake 1/
Mcal; ME/d	7.08 a	7.65 b	7.83b	8.15b	0.15
ME, /; kg DM	2.01a	2.04a b	2.07a b	2.10b	0.02

^{a b c-d} Means within rows not sharing a common superscripts are significantly different (P<0.05); SEM = standard error of the mean

^1/ 1 kg = DOM = 3.8 Mcal ME/kg (Kearl, 1982)