The use of ensiled cassava leaves in diets for growing pigs.

1. The effect of graded levels of palm oil on N digestibility and N balance

Chhay Ty, T  R Preston and  J Ly*

 

University of Tropical Agriculture Foundation
Chamcar Daung, PO Box 2423, Phnom Penh 3, Cambodia
chhayty@utafoundation.org
regpreston@utafoundation.org

* Present address: Swine Research Institute,
PO Box 1, Punta Brava, La Habana, Cuba
jlyca@yahoo.com

 

Abstract

Four Mong Cai x Large White castrate male pigs weighing on average 9.6 kg were alloted at random into four diets to study the effect of graded levels (0, 5, 10 and 15% in dry basis) of refined palm (Elaeis guineensis, Jacq.) oil introduced in diets of broken rice and ensiled cassava leaves to study nutrient digestibility and balance of N according to a 4x4 Latin square design. The silage was made from sun-dried, wilted, chopped leaves of cassava  harvested after 4.5 to 5 months of growth. The cassava leaves were ensiled with 5% of sugar palm (Borassus flabellifer) syrup and stored during 30 days in plastic containers of 100 kg capacity.

The characteristics of the silage were pH 4.10, DM 50.7 %, ash 14.1, organic matter 85.9, NDF 47.0, crude fibre 35.3, and N 3.92 % in dry basis, respectively. The cyanide content of the silage was 110 mg/kg DM. Mean environmental temperature was 35^oC at midday (12:00) during the trial (May 2002). Observed feed intake was slightly lower than that programmed (50 g DM/kg body weight) and was on average 45.6 g DM/kg body weight. A non significant slight increase of feed intake from 88.4 to 92.2% from that programmed was found with increasing levels of dietary palm oil. During the entire trial the pigs were in a positive body weight balance and there were no symptoms of animal discomfort. Dry matter and organic matter digestibilities were decreased as the level of dietary refined palm oil was increased.  Energy digestibility was not significantly influenced by graded levels of palm oil in the diet.  In contrast, ether extract digestibility increased significantly (P<0.001) with increased levels of refined  palm oil in the diet. The digestible energy content of the diets increased from 14.03 to 17.26 MJ/kg DM with increasing levels of palm oil. Neither N digestibility nor N retention were affected by the inclusion of refined palm oil in the diet. N digestibility was relatively low (overal mean, 66.7%) but N retention as related to N digested was high (overall mean, 82.7%).

It is suggested that if refined palm oil is included in the diet up to 15% of the DM, there will be no adverse effect on nutrient digestibility and N balance of pigs fed diets based on high levels of ensiled cassava leaves and broken rice.  

Key words:  pigs, ensiled cassava leaves, digestibility, N retention, refined palm oil

 

Introduction

The use of ensiled cassava leaves for pigs and other animal species has been studied in different opportunities (see for example, Bui Van Chinh and Le Viet Ly 2001). In this connection, it has been shown the potential of leaves from cassava as a protein source in pig nutrition in the tropics (Bui Van Chinh et al 1992; Bui Huy Nhu Phuc et al 1996; Du Thanh Hang 1998; Nguyen Thi Loc et al 2000). On the other hand, considerable efforts have been devoted to study the ensiling process and its relationship with cyanide elimination from the leaves (Bui Van Chinh 1990; Ravindran 1990; Limon 1992; Chhay Ty et al 2001).            

One of the characteristics of the ensiled cassava leaves is the relatively low energy density, due to the fact that the high cell wall content results in decrease in the total tract digestibility of energy. Therefore, the inclusion of a high energy density feedstuff in the diet, such as palm (Elaeis guineensis, Jacq) oil, could facilitate an improved animal performance in diets with a high proportion of cassava leaves, without any deleterious effect on energy utilization by the animals. In this connection, several factors influencing the nutritive value of ensiled cassava leaves have recently been examined (Du Than Hang et al 1997; Nguyen Van Lai and Rodríguez 1998; Du Than Hang 2000; Ly et al 2001). However, little if any is known about the nature of the interdependence of such a mixture of ensiled cassava leaves and palm oil and its effect on the nutritive value of the diet for pigs.

The aim of the present experiment was to study the effect of the inclusion of graded levels of palm oil in the diet on nutrient digestibility and energy balance of pigs fed a high level of ensiled cassava leaves.

Materials and Methods

Location and climate

The experiment was carried out in the ecological farm of the University of Tropical Agriculture Foundation (UTA), located in Chamcar Daung, in the outskirts of Phnom Penh City, Cambodia. The ambient temperature was about 35⁰C in the middle of the day (12:00) during the trial in May 2002.

Experimental feeds

Cassava leaves were harvested after 4.5 to 5 months of growth from farmer’s fields in Kandal province, Cambodia. Stems and petioles were removed from the leaves and then the foliage product was sun-wilted for half a day before being chopped into small pieces and ensiled with 5% of sugar palm (Borassus flabellifer) syrup diluted with water 1:1 (fresh basis). Leaves and syrup were carefully mixed and  stored in plastic bags, inside rigid plastic containers. The bags were tightly closed to prevent air contact and stored for 30 days before feeding. Every container thus prepared contained approximately 100 kg of fresh material. The ensiled cassava leaves had a pH of 4.10 and DM content of 50.7%. Other characteristics of the ensiled product were: ammonia 37.6 mg/100 g DM, total acidity 83.6 meq/100 g, cyanide 111 mg/kg DM.

Four diets (Table 1), were formulated to contain 45% ensiled cassava leaves (DM basis), broken rice and fish meal, partially substituted by refined palm (Elaeis guineensis, Jacq) oil originally from Malaysia and currently available in the local market. Broken rice and fish meal were of Cambodian origin.

 

Experimental design

 

The experiment was done according to a 4*4 Latin Square arrangement of 4 dietary treatments with four Mong Cai x Large White castrate male young pigs weighing on average 9.6 kg. The animals were housed in metabolism cages during the whole trial. The metabolism cages (80 x 80cm) were built to allow the quantitative collection of faeces and urine (Photo 1). The characteristics of the cages have been described elsewhere (Chiev Phiny and Rodriguez 2001). The metabolism cages were installed in an open stable. Each experimental period consisted of five preliminary days when the animals were adapted to the diets followed by another five days for collection of faeces, urine and feed refusal.

Photo 1: The metabolism cage used in the experiment

 

The pigs were fed thrice daily with equal rations at 8:00 am, 12:00 am and 3:00 pm. The cassava leaf silage was mixed with the other components of the ration. Feed intake was programmed to be 50 g DM/kg bodyweight, and water was permanently supplied through drinking nipples. The animals were weighed at the beginning of the trial and every ten days.

.

Data collection

 

Feed refusals and faeces were collected every day and were kept frozen in plastic bags until analysis. A representative sample was obtained from every type of thawed material after a careful homogenization. At the end of each period, feed refusals and faeces were mixed thoroughly by hand and then homogenized in a coffee grinder, prior to taking representative samples that were analysed for DM, N, Crude fibre, NDF, crude fat and ash. Urine was collected in a plastic bucket to which sulphuric acid was added to maintain the pH below 4.0. At the end of each period the volume was measured and a sample analysed for N.

 

Chemical analyses

 

Chemical analyses of the feed ingredients, diets and faeces were undertaken following the methods of Goering and Van Soest (1970) and Van Soest et al (1991) for NDF, and AOAC (1990) for ash, N, crude fibre and ether extract. The DM content was determined using the microwave method of Undersander et al (1993). Fresh faeces were analyzed for pH with a glass electrode. The N content of urine was determined by the AOAC (1990) procedures. All the analyses were conducted in duplicate. The gross energy of diets and faeces was calculated according to energy coefficient values of 5.72, 9.50, 4.79 and  4.05 kcal/per cent of crude protein, ether extract, crude fibre and NFE, respectively (Nehring and Haenlein 1973). Thereafter, total digestibility of energy was estimated by standard methods of calculation. The conversion coefficient of 4.184 kjoule/kcal was used in the appropriate circumstances.

 

Statistical analyses

 

The data were subjected to analysis of variance according to the general linear model of the Minitab software (Minitab release 12; 1998). In the required cases means were separated by the Duncan’s multiple range test procedure (Steel and Torrie 1980). The model used was:

Y_{ijk =} m + Ti + Pj +ak + eijk   where  

 

Y = Dependent variable

m = overall mean

Ti = treatment effect

Pj = period effect

Ak = animal effect

eijk = random error

 

Results

The pigs gained weight during the trial and there were no symptoms of intoxication due to the consumption of ensiled cassava leaves. A slight decrease in voluntary feed intake, relative to the programmed amount, was observed in all treatments (Table 2). However, there was no treatment effect (P>0.05) on this index, which averaged 45.6 g DM/kg body weight.  

 

 

There was no significant dietary effect on measured faecal characteristics (Table 3). The alkaline reaction of faeces was noteworthy. On the other hand, overall faecal DM was relatively high.  

 

 

Overall, digestibility values for DM were low (Table 4). The refined palm oil used in the experiment decreased the digestibility indices of dry matter and organic matter (P<0.01). The digestibility of ether extract increased as the level of palm oil was increased (P<0.001). Digestibility of energy did not change by the introduction of graded levels of refined palm oil in the diet, and was on average 73.3%. As a consequence of higher gross energy values of the diet, the digestible energy content of the diet increased from 14.0 to 17.3 MJ/kg DM when the level of refined palm oil in the diet was increased from 0 to 15%.  

 

 

Figure 1. Relationship between digestibility of ether extract and level of palm oil in pigs

 

On all diets the digestibility of N was rather low; in contrast, the retention of N as percent of intake and of digested N was high (Table 5). There was no effect of the level of palm oil on these parameters.

 

 

Discussion

Feed intake

 

The use of high proportions of ensiled cassava leaves in the diet of pigs could be expected to reduce the voluntary feed intake, mainly due to the bulkiness of this feed. There are no previous reports concerning the effects on voluntary feed intake and growth traits in pigs when high levels of ensiled cassava leaves are included in the diet. In the present study, very few feed refusals were observed (see Table 2), which implies that the bulkiness of the diet was not limiting the feed intake.

 

The cyanide content of the cassava leaves could be another factor that could negatively influence voluntary feed intake of pigs, probably due to the bitter taste of the leaves (Ravindran et al 1987). Even so, González et al (1999) did not find any constraint to feed intake when 30% of cassava foliage from a bitter variety was included in the diet. The  bitter taste of cassava leaves could be highly masked by the strongly acidic nature of the silage, which had an average pH value of 4.10. A long term effect of cyanide on the pig’s voluntary feed intake has not been studied in detail (see for example, Tewe 1992). According to the analyses made on the silage, the cyanide level in the diets was some 50 mg/kg DM. This is below the recommended threshold of safety of cyanide concentration in food for human consumption (Gómez 1991). On the other hand, it was observed during the adaptation period of the animals to the metabolism cage and environment that the addition of sugar palm syrup at the moment of feeding the silage appeared to greatly enhance the voluntary feed intake of the mixed diet.

 

Fibre fractions and nutrient digestibility

Results from this experiment related to nutrient digestibility are in accordance with other previous studies where ensiled cassava leaves from a periodically cut plantation accounted for 50% of the diet (Ly and Pok Samkol 2001). Ly and Pok Samkol (2001) reported a DM digestibility value of 79.6%, which compares well with the data from this study using pigs fed a diet containing 45% ensiled cassava leaves of similar characteristics and no palm oil (77.4%, see table 4). Other data resulting from trials conducted with pigs fed ensiled cassava leaves of a probable high maturity are somewhat lower than those from these results (Bui Hong Ngu Phuc et al 1996; Du Than Hang 2000). It is known that with maturity, the fibrous fraction of cassava leaves changes its structure and proportions (Ravindran and Ravindran 1988), and this could increase the resistance to degradation in the digestive tract of the pigs.

 

On the other hand, Bui Hong Ngu Phuc et al (1996) and Du Thanh Hang (2000) showed that digestibility indices decreased with increasing level of inclusion of ensiled cassava leaves in the diet. However, little if any, is known on the influence of the degree of maturity of the cassava leaves maturity, and in consequence, the effect of possible changes in the linkage of nutrients to the fibre fractions, on nutrient digestibility in pigs. Several authors (King and Taverner 1975; De Goey and Ewan 1975; Kennelly et al 1978; Kennelly and Aherne 1980; Perez 1991) have found that a high content of fibre causes a reduction in the digestible energy concentration in pig rations. In this connection, Den Hartog et al (1988) found that apparent digestibility of organic matter and N were negatively  related to the dietary NDF. Similarly, Sandoval et al (1987) observed that there was a linear decrease in the digestibility of dry matter, crude protein, crude fibre, nitrogen free extract, organic matter and acid detergent fibre with increasing levels of dietary wood pulp. The total tract digestibility of nitrogen in pigs may fall by 1 to 1.5% in response to each 1% increase of dietary crude fibre according to INRA (1984). Other authors (Pond et al 1962; Cole et al 1967; Kass et al 1980; Just et al 1983; Frank et al 1983;  Noblet and Perez 1993) have observed that digestibility of nitrogen decreases with increasing dietary level of fibre. Sauer et al (1980) and Partridge et al (1982) also recognised that apparent crude protein and amino acid digestibility could decrease when additional fibre is included in pig diets.

 

Several factors have been mentioned to explain the mode of action of the different fibre fractions on total tract digestibility. Schneeman (1978) stated that fibre may absorb trypsin and chymotrypsin, as shown by a decrease in the activities of these enzymes. On the other hand, Just (1983) suggested that high levels of fibrous material in the ration could shorten the time for digesta to be enzymatically digested in the small intenstine, where the absorption of almost all nutrients takes place. Whittemore (1998) considered that non-starch polysaccharides reduce the digestibility of amino acid through coating and protecting effects. Some dietary protein is shifted away from the small intestine to the large intestine, where adsorption of amino acids is less efficient (Whittemore 1998).

 

It has been argued that, in contrast with a negative effect of fibre fractions on total tract digestibility of N, ileal digestibility of N is only very slightly affected in pigs fed different types and levels of fibre (Sauer et al 1991). Therefore, a negative effect of fibre on N disappearance in the large intestine, decreasing the extent of this process in this organ, could be even benefical for pigs, since this N is generally absorbed in non-amino acid forms by the pigs (Zebrowska 1973, Just et al 1981). This fact in turn should positively affect the energy metabolism of the animals, since an increase in the Krebs-Henseleit cycle in the liver to eliminate those N-compounds requires a considerable input of ATP. More information is necessary to support this theoretical discussion relating to possible factors influencing digestibility of nitrogenous compounds in pigs fed high levels of ensiled cassava leaves. Nevertheless, as a working hypothesis, it is proposed that a decrease in total tract digestibility of N in pigs fed high levels of cassava leaf silage does not necessarily result in a concomitant decrease in amino acid availability.

 

Dietary fat and nutrient digestibility

The results from the present experiment are in agreement with those from González et al (1999) who studied  graded levels of palm oil up to 10% in diets containing 30% cassava foliage. According to these researchers, digestibility of DM, NDF, N and organic matter was not affected by the level of dietary palm oil. In the Venezuelan report, an improvement in total tract digestibility of ether extract was observed when pigs were fed diets containing 30% of cassava foliage meal with increasing levels of refined palm oil, which also agrees with our results. Balogun and Fetuga (1984) also observed there was no negative effect of palm oil up to 10% of the diet on the N balance of piglets fed on cassava root diets. These observations are in accordance with those from this study. Le Duc Ngoan (1994) reported very low digestibility indices when Colombian palm oil was used in diets of fattening pigs based on sugar cane juice.  It is probable that the small number of observations (n=3) and the use of an indirect method for determining the total tract digestibility could have been factors leading to these low values. In contrast, Morgan et al (1984) found a total tract digestibility of palm oil as high as 95.8% in pigs. Eeckhout et al (1983) found that the digestibility of the ether extract of refined and crude palm oil was 86.0 and 85.4%, respectively.

 

There are a number of factors that can influence the nutritive value of diets containing different types and levels of lipids (Li et al 1990; Pech Sovanno et al 2002). Pettigrew and Moser (1991) and Leibbrandt et al (1995) observed that young pigs are less capable of digesting and utilizing dietary fat than are older pigs. Kurival and Bowland (1962) found that the digestibility of energy did not depend on the level of dietary fat; while Whittemore (1993) suggested that fat products with high levels of free fatty acids are less well digested.

.

Conclusions

 It is concluded that:

·    Up to 15% of palm oil can be included in the diet of pigs fed high levels of ensiled cassava leaves without affecting nutrient digestibility and N balance.

·    Adding palm oil to diets formulated with high levels of ensiled cassava leaves results in an increase in the digestible energy density in such diets.

 

Acknowledgements

The present experiment is part of a study on the use of ensiled cassava leaves and palm oil in pigs, supported by the MEKARN project financed by the SIDA-SAREC Agency. The authors express their gratitude to all the personal of the Ecological Farm, of the University of Tropical Agriculture Foundation, for help with the experiment, especially Mr. Keo Saeth for his assistance in taking care of the animals. Thanks are also expressed to Mr. Pok Samkol for analytical assistance in the laboratory of the Ecological Farm.  This paper formed part of the MSc thesis (MEKARN-SLU, Uppsala, May 2003), of the senior author.

 

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Received 21 May 2003; Accepted 1 July 2003 

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