Livestock Research for Rural Development 13 (4) 2001

Citation of this paper

Effect of a single drench of cooking oil on the rumen ecosystem and performance of young local "yellow" cattle fed rice straw and cassava foliage  

Mom Seng, T R Preston*, R A Leng** and U ter Meulen***

 Royal University of Agriculture, P.O.Box 2696, Phnom Penh, Cambodia.

*University of Tropical Agriculture Foundation, Phnom Penh, Cambodia

** PO Box 361, Coolum Beach QLD 4573, Australia

***Institute of Animal Physiology and Animal Nutrition, Department of Tropical Animal Nutrition, Georg-August-University, Kellnerweg 6, 37077 Göttingen, Germany.



The following study aimed to improve the utilization of available resources and develop a system for fattening local cattle in Cambodia. It is based on two principles: ruminants use their feed more efficiently when protozoa are absent from the rumen and cassava foliage has been found to be a source of by-pass protein for ruminants. Twelve growing local "Yellow" cattle of mean weight 114 kg (SE ±4.35) received a basal diet of ad libitum rice straw and a rumen supplement (13% urea; 3% diammonium phosphate) at 300g/head/day. The 4 treatments, arranged according to a 2×2 factorial design, were the basal diet alone (RS), or RS plus fresh cassava foliage at 3% of LW (fresh basis) (RSC), RS plus a single oil drench (cooking oil at 5ml/kg LW) (RSO), or RSC with oil drench (RSCO). Rumen samples were taken at the 7th, 14th, 28th, 56th and 84th day related to the day of the oil drench to determine pH, ammonia concentration and protozoa count. Daily feed intakes and fortnightly live weights were recorded for 4 months.

The oil drench reduced the protozoa population. However, there was a rapid re-infestation of the small protozoa (mainly Entodinia) to a level comparable to the control groups. Only a few large protozoa (mainly Polyplastron and Holotrichs) were observed, being present in significantly smaller numbers than in non-oil animals. The overall protozoal biomass in the oil groups throughout the 84 day trial was estimated to be at least 4 times lower than in the non-oil groups. Rumen ammonia concentrations were significantly lower in oil-drenched animals. Feed intake increased significantly in both oil and non-oil animals when cassava foliage was given but was not affected by the oil drench.

Growth rates were increased significantly by the oil drench and the cassava supplement. The mean values were 53, 124, 210 and 302 g/day (SEM ± 30) for RS, RSO, RSC and RSCO, respectively.

Key words: Cattle, growth, cassava foliage, oil drench, rumen ecosystem, protozoa


Like in other developing countries in the region, large ruminants in Cambodia rely mainly on rice straw with addition of other crop residues and grass from uncultivated land. These feeds are imbalanced in essential nutrients and are of low digestibility, thus  production levels are low. Several approaches have been made to improve the utilization of rice straw such as treatment with ammonia and supplementation with urea-molasses blocks, green forage and sources of bypass protein (Chenost and Kayouli 1998). Rumen manipulation by removing the protozoa has been shown to improve the levels of production of ruminants fed low-protein diets (Bird et al 1979). Lipids are toxic to rumen ciliate protozoa (Newbold and Chamberlain 1988) and this approach for reducing rumen protozoa was used successfully by Nguyen Thi Hong Nhan et al (2001) with positive effects on growth rates of cattle.

The purpose of this study was to make a preliminary investigation into the feasibility of introducing this practice to the Cambodia situation to improve the utilization of the rice straw as the basal diet of local “Yellow” cattle. Cooking oil, which is available in the local markets, was used as the lipid source and fresh cassava foliage as the protein supplement.

Material and Methods

The experiment took place from November 2000 to April 2001 at the ecological farm of the University of Tropical Agriculture, located in the Royal University of Agriculture, Chamcar Daung, some 15 km from Phnom Penh, Cambodia.

Experimental design

Twelve local “Yellow” cattle with mean live weight of 114 kg (SE ±4.35), received a basal diet of ad libitum rice straw and a rumen supplement (13% urea; 3% diammonium phosphate) at 300g/ head/ day. The 4 treatments, arranged according to a 2*2 factorial design, were:

·        RS:  The basal diet of rice straw and rumen supplement
·        RSO: The basal diet and a single oil drench (cooking oil at 5ml/kg liveweight)
·        RSC: The basal diet with fresh cassava foliage at 3% of live weight
·        RSCO: The basal diet with cassava foliage and oil drench

All the animals were housed in individual pens with a concrete floor in a shed roofed with Imperata leaves and open at the sides.  The animals that received the oil drench were housed in adjacent pens in one side of the shed separated by a space of 3m from the six animals that did not receive the oil.  All feeding, weighing and sampling activities were done first with the oil-drench animals and afterwards with those not given the oil.

Diet and feeding procedure

All animals received 300 g/day of a rumen supplement containing 13% of urea (Table 1). .

Table 1. The composition of the rumen supplement


Percentage by weight

Sugar palm syrup  (75 brix)




Rice bran




Diammonium phosphate








 The cassava foliage was the regrowth of cassava managed as a semi-perennial forage with repeated harvests at 50 to 80 day intervals (Preston et al 2000). The aerial part was harvested by cutting the stem at about 70 cm above the ground. The foliage was cut and chopped in pieces of about 10 cm, with no separation of leaves, stems and petioles, prior to feeding it to the animals. The feeds were divided into three meals per day. The feeding order of the RS and RSO groups was rice straw followed by 150 g of rumen supplement then 150 g of rumen supplement followed by rice straw. The RSC and RSCO groups received rice straw followed by rumen supplement, cassava foliage as a single meal and finally rumen supplement and rice straw. The animals had free access to fresh and clean water. Rice straw was purchased from local farmers and was sampled for analysis once as at the time of purchase of each new batch.  The cassava foliage was sampled every week.

 Oil treatment

The animals allocated to RSO and RSCO were adapted to the diets for 2 weeks before being given the oil. The oil used in this study was cooking oil available on the local market "Cabbage Brand". On day “–1” they were fasted but with access to water for 18 hours until 08:00 the next day (day 0) when they were given the oil drench. The quantity of oil was 5 ml/kg live weight and it was administered directly into the rumen using a stomach tube.


Daily feed offered and refused and fortnightly live weights were recorded for a 4 month period. The growth rate was calculated from the linear regression of live weight against time. Rumen samples were taken by stomach tube from all animals one hour after the first feeding on the 7th, 14th, 28th, 56th and 84th day after administration of the oil. Measurements were made of pH, ammonia and the protozoa count. The pH of the rumen fluid was determined immediately by using a glass electrode. A sub-sample of 10ml of rumen fluid  with 1 ml of formal saline was taken for the counting of the protozoa.. Another sub-sample, for ammonia determination, was acidified with concentrated sulphuric acid. The sub-samples were kept in a refrigerator (-20ş C) until the analysis and counting were done. Ammonia was determined by distillation according to the procedure described by Preston (1995).

Protozoa were counted using the relative counting method (R A Leng, personal communication). One drop of diluted sample (mixed well before sampling) was placed on a slide and a cover slip added. The protozoa were then counted in 20 different views on the slide, under 10x magnification, working progressively across the slide and down. The procedure was repeated 2 to 3 times for one sample. The calculation was the average of counts knowing the area and volume of the sample under the slide. The average count of 20 views was recorded and then the average between the slides for one sample was calculated (P). The  volume (V) of rumen liquor in one drop was calculated from the average weight of 100 drops. The protozoa count per ml of rumen fluid was then:


where “A” is the area of the microscope field at 10x magnification and B is area of cover slip. Protozoa were divided into large which were roughly 80µ and small which were  roughly 20µ.

Statistical analysis

The data were analysed according to the analysis of variance procedure using the general linear model (GLM) in SAS (Statistical Analysis System) version 6.12.  


Chemical composition of the diets

The dry matter content of samples of the rice straw and cassava foliage used in the experiment was in the range of 80 to 90% and 21 to 24%, respectively. Crude protein content (N x 6.25) in dry matter ranged  from 2.5 to 4 % and 18 to 22 %, respectively.

Table 2.  Mean values for effect of oil drench (5 ml/kg LW) on growth and rumen parameters in local "Yellow" cattle






Significance of











Growth parameters










Initial LW, kg










Final LW, kg










Daily LW gain , g










DM intake, kg/day










Feed conversion#










Rumen parameters










Protozoa (x 10 -4/ml)










Small protozoa##










Large protozoa##




















NH3-N, mg N/litre










RS = rice straw; RSC= rice straw+ cassava foliage
SEM= standard error of the mean;
ns= non-significant (P>0.05); * and ** denote significance at P<0.05and P<0.01, respectively.  
# DM intake/gain in LW.

## Small protozoa, roughly 20µ, mainly Entodinia;
### Large protozoa, roughly 80 µ, mainly Polyplastrons and Holotrichs

Growth parameters

Feed intake fell dramatically after oil administration but returned to normal in one week. Supplementation with cassava foliage increased the feed dry matter intake in both oil and non-oil animals but the oil drench had no effect on this parameter (Table 2). Both the oil drench and cassava foliage increased the growth rate and improved the feed conversion. The highest growth rate was achieved with the  combination of oil drench and cassava forage supplementation (Figure 1).


Figure 1. Least square means of daily live weight gain
 of local "Yellow" cattle with or without oil drench
Each bar represents the least square mean (±SEM)
(RS = rice straw, RSC= rice straw + cassava foliage

Rumen parameters

The small ciliate protozoa were mainly entodinia and the large one were mainly polyplastron and holotrichs. There was a rapid re-infestation by the small protozoa (Figure 2.). At first observation, on day 7, the populations of small protozoa were 0.51 and  3.78 (104/ml)  for the oil and non-oil treatments; while on day 84 the respective counts were 3.81 and 3.48 (104/ml).

The population of large protozoa was reduced markedly (P<0.01) in the cattle given the oil drench and this effect persisted throughout the experiment. On the 7th day after treatment the numbers of large protozoa were 0.26 and 0.0053 (104/ml) and on day 84 they were 0.25 and 0.055 (104/ml) for non-oil and oil-drenched animals, respectively (Figure 2.). The least square means of the population of large protozoa during the whole experiment of 84 days were 0.25 and 0.032 (104/ml), for non-oil and oil-drenched animals, respectively.


The rumen pH was not affected by the oil drench nor the cassava foliage supplement


The ammonia concentration in the rumen fluid (Table 2) of cattle given the oil drench was lower than in the non-oil treatments (P<0.01).  There was no effect of the cassava forage supplement.



 Figure 2. Numbers of large ciliate protozoa (mainly Polyplastrons and Holotrichs)and small ciliate protozoa (mainly Entodinia)  at different periods following an oil drench. Each bar represents the least square mean (±SEM).


Rumen parameters

The effect of the oil drench, which significantly reduced the protozoa population (Figure 2), is in agreement with various studies (Ikwuegbu and Sutton 1982; Sutardi and Jalaludin 1996; Nguyen Thi Hong Nhan et al 2001). Newbold and Chamberlain (1988) indicated that lipids are  toxic to protozoa. The toxic effect could be due to increasing acidity, resulting from the  free fatty acids liberated from the oil. Protozoa are more sensitive to pH than bacteria (Newbold et al 1986a).

The reappearance of protozoa on the 7th day after treatment (Figure 2) is in agreement with the finding of Eadie and Shand (1981) who used a detergent (Synperonic) at 0.55 g/kg LW as defaunation agent.  They found that many ciliates were killed but 2 hours after treatment live organisms could still be found and the ciliate population returned to normal by the 6th day. In contrast, Nguyen Thi Hong et al (2001) found that their cattle stayed free of protozoa until the 15th day after treatment.  Nguyen Thi Hong Nhan et al (2001) used a higher level of oil (6 ml/kg live weight) compared with our study (5 ml/kg live weight). The other possible reason could be the contamination from the control group, even though a space of 3m was maintained between the two groups of oil and non-oil animals, and feeding, watering cleaning, sampling and measurements were done separately.

During the recovery stage, entodinia dominated which is quite similar to the findings of Soetanto (1985). Entodinia are more resistant to acidity and have a more rapid growth rate as compared with other genera (Williams and Coleman 1992). Entodinia multiply up to 4 generations in a day even without any allowance for the flow of rumen contents (Warner 1962).

The numbers of protozoa were low compared to studies reported by Warner (1962) and  Bird and Leng (1984) but similar to the findings of Kudo et al (1990) and Nguyen Thi Hong Nhan et al (2001),  who found the protozoa population to be in the range from 0.8 to 4.6 x 10-4 /ml.  The “relative” count method may under-estimate the true population.  Also a sample taken by stomach tube is unlikely to be representative of the overall population. Contamination with saliva would also result in an under-estimate of the protozoa population. 


There was no effect of  the oil drench on rumen pH. This result is in agreement with findings of Newbold et al (1986b) who found that defaunation or refaunation had no effect on rumen pH. In contrast, Nguyen Thi Hong Nhan et al (2001) reported that pH was lower in defaunated animals. The method of sampling rumen fluid by stomach tube, with variable degrees of contamination by saliva, could be the explanation of the failure to observe differences in the present study. In animals on high starch diets, the rumen ecosystem of ciliate-free animals becomes unstable and this leads to ruminal disorders such as acidosis (Itabashi et al 1984). In such a situation, protozoa play an important role in slowing down the fermentation by ingesting starch grains and taking up soluble sugars and converting them to storage polysaccharides (Schwartz and Gilchrist 1975). In our study, roughage provided over 80% of the diet hence the potential role of protozoa as a  stabilizing influence on the fermentation was not an issue.


The lower ammonia concentration in oil-drenched animals is in agreement with results of various authors (Abou Akkada and El-Shazly 1964; Ikwuegbu and Sutton 1982; Kayouli et al 1983/4; Soetanto 1985; Nguyen Thi Hong Nhan et al 2001). Protozoa have high a capacity for proteolytic and deaminase activities (Ushida et al 1984; Hino and Russel 1987); and there is an increase in the rumen outflow of protein from bacteria and fungi in the absence of protozoa (Newbold and Hillman 1990). There are several reports (Hungate 1966; Kayouli et al 1983/1984; Newbold and Hillman 1990) that defaunation or reduction in the  protozoa population leads to an increase in the bacterial population , which uses ammonia as the source of nitrogen for cell synthesis. Thus more ammonia is being used when the bacterial population is increased. The reduction in ammonia concentration could thus be due to high rate of ammonia assimilation by bacteria, as well as reduced sources of ammonia entering the pool when protozoa are absent or present in small numbers.

Although protozoa returned within one week of giving the oil drench, and the small ciliate protozoal population reached a level corresponding to non-oil animals within 2 weeks, there was a significant reduction of large protozoa in oil-drenched animals throughout the 84-day trial. In non-oil animals, the large protozoa comprised 7% of the total protozoa biomass, compared to only 1% for the oil-drenched animals. The difference in numbers of large ciliate protozoa between treatments markedly affects the total protozoa biomass because large ciliate protozoa are about 100 times bigger than entodinia (Warner 1962). It was estimated that the protozoa biomass of non-oil animals was four-fold higher on average than in the oil-drenched animals during the 84-day trial. The higher the biomass of total protozoa the more competition for space and food with other microorganisms. Furthermore, large ciliate protozoa (holotrichs and polyplastrons) have longer turnover rates and only a small percentage of these protozoa wash out from the rumen while small entodiniomorphid protozoa have a similar turnover rate to the turnover rate of the rumen fluid of cattle and sheep (Leng 1989). Protozoa contribute little to the total microbial outflow from the rumen (from 5 to15% according to Leng 1989 and up 20% according to Ushida et al 1984). Thus reducing the protozoa biomass in the rumen will lead to increased availability of microbial protein to the host.  An increase in N retention as a consequence of defaunation was reported by Veira (1986),  Bird et al (1994) and Santra and Karim (2000).

Growth parameters

Feed intake and growth rate increased and feed conversion rate was better when cassava foliage was included in the diet. This is agreement with the report of Do et al (2001) who used fresh cassava foliage as a supplement for cattle fed rice straw, and Ffoulkes and Preston (1977) who fed fresh cassava foliage to cattle fattened on a diet of molasses-urea. Many studies have shown increases in digestibility and dry matter intake, and improved rumen function, when roughage of low nutritive value is supplemented with green forage (Bird et al 1994; Leng 1997; Nguyen Van Thu and Uden 2001).

Appetite was depressed following the oil drench but returned to normal within one week. Similar findings were reported by Eadie and Shand (1981) and Chaudhary and Srivastava (1995). The depression may be due to several reasons such as reduction of the rumen microbial population, as both bacteria and fungi as well as protozoa are affected by the oil treatment. An increase in heat increment resulting from the booster dose of the oil drench could be another factor.

The reduction of the protozoa population had no effect on feed intake measured over the whole period, which is supported by earlier reports (Bird et al 1979, 1994; Bird and Leng 1984; Chaudhary and Srivastava 1995). Digestibility is one factor which influences feed intake. The effect of defaunation upon feed digestibility is still debated. Defaunation or reduction of the protozoa population led to depressed digestion of fibre according to Ikwuegbu and Sutton (1982) and Chaudhary and Srivastava (1995). In contrast, Bird et al (1994) and Nguyen Thi Hong Nhan et al (2001) indicated that defaunation was associated with an increase in in sacco digestibility.

The most probable explanation for the increase in growth rate, without changes in feed intake, of the cattle drenched with oil is the reduced protozoa biomass in the rumen. This interpretation is supported  by the findings of Bird et al (1979), Bird and Leng (1984), Santra and Karim (2000) and Nguyen Thi Hong Nhan et al (2001). Conflicting reports are those by Chaudhary and Srivastava (1995) and Abou Akkada and El-Shazly (1964), in which there were no differences,  or reduced animal performance, caused by defaunation. The differences could be due to the nature and level of protein in the diets. The diets used by Chaudhary and Srivastava (1995) and Abou Akkada and El-Shazly (1964) were based on concentrates and contained high concentrations of protein, with digestible crude protein up to 12% (Chaudhary and Srivastava 1995). The basal diet used in the study reported here was rice straw, a roughage with low crude protein content (average of 30 g/kg DM). This was chosen because it is widely use as feed for ruminants in Cambodia.

The oil drench and cassava foliage supplement appeared to have an additive effect on animal performance, presumably because both contributed to an enhanced flow of protein to the intestines.


·       Cooking oil, which is freely available in all local markets in Cambodia, can be used as a defaunation agent.

·       Administration of a single drench of the oil (at the rate of 5 ml/kg live weight), and supplementation with fresh foliage from cassava re-growth (30 g/kg live weight) enhances both rate of live weight gain and feed conversion of cattle fed rice straw and limited amounts (300 g/day) of a urea-rich (15%) rumen supplement.

·       There was a synergistic effect of the oil drench and the cassava foliage on animal performance.


Financial support was mainly given by GTZ (The German Agency for Technical Co-operation) and the University of Tropical Agriculture Foundation. The support from these organisations is gratefully acknowledged.


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