Livestock Research for Rural Development 14 (6) 2002

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The effect of methionine on digestion indices and N balance of young Mong Cai pigs fed high levels of ensiled cassava leaves

J Ly 

University of Tropical Agriculture Foundation
Royal University of Agriculture, Chamcar Daung, Phnom Penh, Cambodia  


Two groups each of 8 Mong Cai castrate male pigs of mean initial weight 19.2 and 22.5 kg were used in two experiments to assess N balance in animals fed ensiled cassava leaves supplemented with either 0.5 or 1.0% DL-methionine. The pigs were fed diets containing sugar palm (Borassus flabellifer) syrup, dried fresh water fish and ensiled cassava leaves (73.5% of the daily ration in dry basis), and were allocated to level of supplementary methionine according to a change over design. The silage was made from sun-dried, wilted, chopped leaves and petioles in two batches (one per experiment) of cassava foliage harvested after eight weeks of re-growth and thereafter ensiled during four weeks. The pH was 4.04 and 3.46, DM 46.2 and 48.3%, N 3.20 and 3.35% (in DM) in each silage batch respectively. 

The higher level of  DL-methionine in the diet in experiment 2 appeared to result in an increase in the digestibility of dry matter and organic matter. There were also trends for N digestibility and N retention to be improved with methionine supplementation In vitro (pepsin/pancreatin) N digestibility of the silage was high (65.2-66.6%). 

It is suggested that N balance in young pigs fed very high levels of ensiled cassava leaves can be improved by supplemetation with DL-methionine.

Key words: DL-methionine, ensiled cassava leaves, N balance, pigs,


The use of high levels of ensiled cassava leaves in pig nutrition is a possible alternative in tropical countries where cassava is a common local crop. In this connection, a complementary source of protein such as dried fish can be used as a possible source of sulphur amino acids, which in turn not only can balance the amino acid profile of the diet since cassava leaves are rather poor in methionine (Eggum 1970), but at the same time it may facilitate to some extent the detoxification process (Tewe 1992) of the remaining cyanide content in the ensiled cassava foliage. Ly and Pok Samkol (2001) have shown that total N digestibility by pigs of ensiled cassava leaves can be high when the dietary protein supply is high and rich in sulphur amino acids. 

The addition of DL-methionine to diets high in ensiled cassava leaves could be another alternative to be taken into account in this feeding system (Ly and Rodriguez 2001). Thus, the present paper describes several studies concerning the effect of three levels of DL-methionine supplementation in young Mong Cai pigs fed high levels of ensiled cassava leaves in the diet.

Materials and Methods  

Two experiments were conducted to evaluate the effect of DL-methionine supplementation on digestion indices and N balance of pigs. The DL-methionine was of commercial origin. Two groups each of 8 Mong Cai, castrate male pigs of 19.2 and 22.5 kg initial live weight on average were fed diets containing sugar palm (Borassus flabellifer) syrup, dried fresh water fish  and ensiled cassava leaves (Table 1). In experiment 1, the supplementation with DL-methionine was 0 and 0.5% and in experiment 2 it was 0 and 1.0%. The allocation of pigs to DL-methionine supplement level was according to a two-period balanced changeover design (Gill and Magee 1976; Gill 1978). The process of ensiling the cassava leaves was as previously described (Ly and Pok Samkol 2001). 

Table 1. Main ingredients and chemical composition of the diets (percentage in dry basis except for dry matter)


DL-methionine, %




Sugar palm syrup




Dry fresh water fish




Ensiled cassava leaves












Vitamins and minerals4





Dry matter








Organic matter












1 Average of experiments 1 and 2
2 Experiment 1
3 Experiment 2
4 According to NRC (1998) requirements for pigs

The silage was made from sun-dried, wilted, chopped leaves and petioles in two batches (one per experiment) of cassava foliage harvested after eight weeks of re-growth and thereafter ensiled during four weeks. The results corresponding to representative samples of silages used during the conduct of the balance trials (four per batch) are listed in Table 2.  

During the adaptation period, observations of feed intake were made in order to adjust animal consumption thus avoiding large amounts of feed refusal. On the other hand, preliminary formulations were made to use diets containing 75% of ensiled cassava leaves given in two daily meal at 7:00 am and 3:00 pm. Daily feed intake was calculated to be of the order of 30 g DM/kg body weight. Diluted sugar palm syrup (1:1 by weight with water) was mixed with the dried fish, minerals and vitamins and DL-methionine, and then was given to the pigs. 

The original sugar palm syrup contained N 0.27 and ash 0.89% in dry basis and the diluted product (1:1 by weight) contained DM 43.3 ± 0.23 %, brix 42.1 ± 0.40 and had a pH value of 4.66 ± 0.05 (average of two batches). 

After the complete consumption of this mash, the ensiled cassava silage was offered to the animals. Water was always available through drinking nipples. The amount of all feed refusals was recorded the following day at 6:00 am and samples were obtained for analyses. 

Table 2. Characteristics of the ensiled cassava leaves

Ensiled cassava leaves
Experiment 1 Experiment 2


4.04 3.46

Total acidity, mequiv/100 g fresh material

14.0 17.1

Volatile acidity, % total acidity

14.5 24.6

Ammonia, mequiv/100 g fresh material

40.2 37.0

DM, %

46.2 48.3

Organic matter, %

92.4 91.3

NDF, %

61.3 59.1

N, %

3.20 3.35

Cyanide, mg/kg DM

108 115

DM solubility in water, %

42.8 46.4

Water holding capacity, g water/g DM

6.29 6.75

A preliminary adjustment period of five days was followed by another five days of collection of faeces and urine. Other details concerning pig housing and daily routine carried out during the trial have been described elsewhere (Ly and Pok Samkol 2001). 

The NDF content in faeces and feeds was carried out according to Van Soest et al (1991). DM concentration in feeds and faeces was determined using the microwave method of Undersander et al (1993) whereas the level of faecal short chain fatty acids (SCFA) and ammonia were determined as described elsewhere (Ly et al 2001). Faecal pH was measured with a glass electrode. In addition the in vitro pepsin/pancreatin technique was conducted for N evaluation in samples of fresh water fish and ensiled cassava leaves according to the method of Dierick et al (1985) as previously outlined by Ly and Pok Samkol (2001). Casein of reagent quality was employed as a protein standard. In addition, water holding capacity (WHC) of the ensiled cassava leaves was assayed as suggested by Leterme et al (1998): one gram of dry and ground ensiled cassava leaves was mixed with 20 ml of distill water, then left to rest during 16 hours. The sample was filtered with the aid of the gentle suction of a commercial dust aspirator and the remaining water was considered as the liquid that the sample could retain. Dry matter solubility of the silages was assayed in a commercial washing machine (Ly and Preston 2001). 

Total acidity was estimated in the silage following Chhay Ty et al (2001) and volatile acidity was determined by steam distillation of a supernantant aliquot prepared from a silage slurry (1:4 in water, by weight), then titrating the resulting distillation product. The cyanide content was measured in the opened silage by the distillation method described in AOAC (1990).  

In both experiments means were contrasted by the analysis of variance technique as described by Steel and Torrie (1980). Data were processed using the software package of MINITAB (Ryan et al 1985).

Results and Discussion 


The current studies were conducted during the raining season in Cambodia (August and September 2001) and air temperature at 12:00 am was 33.5 ± 2.5ºC. During the experiments there were no symptoms of animal discomfort due to the consumption of high amounts of ensiled cassava leaves in the diet. All the animals were in positive weight balance and average daily gain during both experiments was 143 ± 25 g. 

The characteristics of the ensiled cassava silages used in this study were similar to others previously prepared (Ly and Pok Samkol 2001). In this connection, the neutralizing capacity or total acidity defined according to Chhay Ty et al (2001), was 14.1 and 17.1 mequiv NaOH/100 g fresh material, from which 14.4 and 24.5% was volatile acidity only. In this connection, Chhay Ty et al (2001) reported pH and neutralizing capacity of approximately 3.9 and 12 m-equiv/100 g in fresh Cambodian ensiled cassava foliage. 

Feed consumption 

Feed consumption recorded in both experiments was 93.0 ± 4.9% of the planned feed intake (30 g DM/kg body weight), indicating a rather slight decrease of voluntary feed intake. As observed elsewhere (Ly and Pok Samkol 2001), the pattern of feed intake was characteristic, with all animals consuming very quickly the sugar palm syrup. A slight decrease of consumption of ensiled cassava leaves was evident in both experiments, and as a consequence the proportion of the silage in this study was 73.5% in dry basis. Even so, this figure is very high, and was equivalent to a consumption of ensiled cassava leaves of 20.5 g DM/kg body weight, or 42.5 to 44.4 g fresh silage/kg body weight.  

It has been proposed that the voluntary feed intake of pigs is largely governed by the bulkiness of the diet (Kyriazakis and Emmans 1995). Therefore, it could be thought that ensiled cassava leaves would be a type of feed, the intake of which might be limited due to its bulkiness. In the current study, the "bulkiness" properties of the ensiled cassava leaves were relatively high, as compared to other conventional fibrous feeds (Kiryazakis and Emmans 1995; Tsaras et al 1998). 

Table 3. Nutrient digestibility and N balance in pigs

DL-methionine, %

SE ±




DM digestibility, %

Experiment 1





Experiment 2





Organic matter digestibility, %

Experiment 1





Experiment 2





NDF digestibility, %

Experiment 1





Experiment 2





N digestibility, %

Experiment 1





Experiment 2





N retention, % consumption

Experiment 1





Experiment 2





N retention, % digestion

Experiment 1





Experiment 2





* P<0.05; ** P<0.01

As was to be expected, the digestibility indices for dry matter and organic matter were lower in the present study (Table 3) than in a previous experiment reported by Ly and Pok Samkol (2001), reflecting the respective levels of cassava leaf silage in the diet (73% versus 50% of the diet ). The substantial increase of cell walls in the diet undoubtedly was responsible for the depression in nutrient digestibility as observed by several authors (Fernández and Jorgensen 1986; Close 1993; Bach Knudsen and Jorgensen 2001). The higher level of  DL-methionine in the diet in experiment 2 appeared to result in an increase in the digestibility of dry matter and organic matter. As there were also trends for N digestibility and N retention to be improved with methionine supplementation, the implication is that the effect was mediated though a better balance of amino acids at the sites of metabolism, and / or the methionine assisted in the detoxification of the HCN. A similar trend for a positive effect of DL-methionine addition on N digestibility was observed in pigs fed high levels of full-fat rubber seeds (Pok Samkol et al 2002), and water spinach (Ly et al 2002).  NDF digestibility was high with or without methionine supplementation,  suggesting that the physico-chemical characteristics of cassava leaves favor cell wall degradation in the alimentary canal. In this connection, Le Goff et al (2002) have suggested that the botanical origin of fibre can affect its  digestibility in pigs, and this may be more decisive than other factors (Varel and Yen 1997).   

Faecal characteristics 

A trend was observed for faecal pH to increase and DM concentration in faeces to decrease with increasing levels of DL-methionine in the diet (Table 4). Similar trends for faecal concentration of ammonia to increase (P<0.01) and of SCFA to be depressed with more methionine in the diet were apparent. There is no apparent explanation as to why addition of methionine should affect the excretion of these metabolites, which result from microbial fermentation in the large intestine. On the other hand, the fresh faecal output was very high, on average 1550 g/kg DM intake, indicating the bulkiness effect of the ensiled cassava leaves. A high fresh material excretion via faeces has been observed in pigs given a diet with 80% alfalfa meal (see Varel 1987). 

Table 4. Faecal characteristics of pigs fed ensiled cassava leaves and methionine

DL-methionine, %

SE ±




Faecal pH

Experiment 1





Experiment 2





DM, %

Experiment 1





Experiment 2





SCFA, mmole/100 g DM

Experiment 1





Experiment 2





Ammonia, mmole/100 g DM

Experiment 1





Experiment 2





Faecal output, per kg DM intake 

Fresh material, g

Experiment 1





Experiment 2





DM, g

Experiment 1





Experiment 2





Water, g

Experiment 1





Experiment 2





SCFA, mmol

Experiment 1





Experiment 2





Ammonia, mmol

Experiment 1





Experiment 2





* P<0.05; ** P<0.01; *** P<0.001 

Organic matter digestibility coefficients in individual pigs varied widely from a low value of 62% to a high value of 83% and were negatively related with faecal outputs of ammonia and SCFA (Figure 1). It seems reasonable to assume that when digestibility is high there is less substrate available for fermentation in the large intestine and hence reduced production of the metabolic products of microbial fermentation.  According to Varel et al (1984), a low faecal output of SCFA and ammonia can be interpreted as an enhanced metabolite absorption across the colonic wall and / or less SCFA and ammonia production.

Figure 1: Relationship between organic matter digestibility and output of metabolites
in faeces of pigs given diets rich in ensiled cassava leaves

The results obtained in the current study concerning N retention suggest that pigs can make an efficient use of the  N compounds contained in ensiled cassava leaves. This idea is in line with data reported by Ly and Pok Samkol (2001) and fully supports the statement that ensiled cassava leaves prepared from foliage periodically harvested has a nutritional advantage over silage prepared with foliage collected at the moment of  harvesting the roots (Ly and Rodríguez 2001).

In vitro N digestibility of the two batches of ensiled cassava leaves was very similar and high (Table 5). On the other hand, the comparison between in vitro N digestibility of ensiled cassava leaves and dried fish was in agreement with other previous results from this laboratory (Ly and Pok Samkol 2001; Ly et al 2001), indicating the high in vitro digestibility of dried fish.

Table 5. In vitro digestibility of ensiled cassava leaves

In vitro digestibility, %


Organic matter


Ensiled cassava leaves

Experiment 1




Experiment 2




Dried fresh water fish




SE ±




In vitro DM digestibility of casein was 98.8 ± 0.3%
*** P<0.001;  ab  Means within the same column with different superscripts differ significantly (P<0.05)


It is suggested that N balance in young pigs fed very high levels of ensiled cassava leaves can be improved by supplementation with DL-methionine.


The present investigation is part of a collaborative work between the University of Tropical Agriculture Foundation and the Swine Research Institute, Havana, Cuba. Special thanks are given to the personal of the Institute for assistance in literature searching and to Mr. Pok Samkol from the UTA Foundation, for his analytical support in the laboratory. The preparation of the silage was in the hands of Mr. Chiev Phiny to whom the author is very grateful.


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Received 1 November 2002

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