The use of ensiled cassava leaves in diets for growing pigs. 2. The influence of type of palm oil and cassava leaf maturity on digestibility and N balance for growing pigs

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

* Visiting researcher at UTA, 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 of mean initial weight  20.7 kg were allocated at random into four treatments according to a 4x4 Latin square arrangement to study the influence on digestibility indices of crude or refined palm (Elaeis guineensis) oil and the maturity of cassava leaves prior to ensiling. The silage was made from sun-dried, wilted, cassava leaves harvested after 4.5 to 5 months of growth (from farmers’ fields, managed for root production) and from young cassava leaves, which were harvested after 2 months of regrowth (from the UTA ecological farm). Mean environmental temperature was 30^oC at midday (12:00) during the trial from 28 July to 3 September 2002.

 

The characteristics of the silages were pH 3.93, 4.00; DM 38.5, 34.2; NDF 25.4 and 23.5; CP 24.5, 23.6 in dry basis, for young and old leaves, respectively. The cyanide content of the silage was 200 and 97.2 mg/kg DM for young and old cassava leaf silage, respectively. Feed intake was on average 44.3 and 41.7g DM/kg bodyweight for young and old cassava leaf silage, respectively and 44.7 and 41.1g DM/kg body weight for refined and crude palm oil, respectively. There was no significant interaction (P>0.05) among any factors for digestibility indices between the maturity of the cassava leaves and type of palm oil. Digestibility was higher for young versus old cassava leaves for DM (P<0.001), organic matter (P<0.001), crude fibre  (P<0.05), NDF (P=0.07), ether extract ( P<0.05), NFE (P<0.05) and energy (P<0.05). N balance indices also appeared to favour silage from young cassava leaves compared to old leaves. There was no significant effect of type of palm oil on nutrient digestibility or N balance indices.

 

It is suggested that the nutritive value for pigs of ensiled cassava leaves can be improved if young instead of old leaves are used for ensiling. Crude palm oil could be used in those places where it is available instead of refined palm oil, thus avoiding the extra cost of refining the product.

 

Key words: Cassava, ensiling, digestibility, leaves, maturity,  N balance, palm oil, pigs

 
 

Introduction

Many experiments have been carried out which demonstrate the potential value of using ensiled cassava leaves 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; Du Thanh Hang 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). However, there appears to be no information on the effect of the age of the cassava leaves used in the ensiling process on nutrient digestibility and growth performance of pigs.

 

One of the characteristics of ensiled cassava leaves is the relatively low energy density, due to the high cell wall content. Therefore, the inclusion of a high energy density feed in the diet, such as palm (Elaeis guineensis, Jacq) oil, could be a way of facilitating the use of higher levels of cassava leaves in the diet. There are favourable reports on the use of high levels of palm oil in pig diets where the protein supplement was soya bean meal (Ocampo 1994; Le Duc Ngoan et al 1994). However, no studies have been done on the use of palm oil in diets in which the protein has been derived from cassava leaf silage.

 

The main aim of the present experiment was to study the effect on nutrient digestibility and N balance in pigs of using silage made from old or young cassava leaves, with crude or refined palm oil as the energy supplement.
 

Materials and Methods  

Location and Climate

This experiment was carried out in the ecological farm of the University of Tropical Agriculture Foundation (UTA) at the Royal University of Agriculture, located in Chamcar Daung, in the outskirts of Phnom Penh City, Cambodia. Mean environmental temperature was 30^oC at midday (12:00) during the trial  from 28 July to 3 September 2002.

Experimental animals and design

Four Mong Cai x Large White castrate male pigs with an average initial body weight of 20.7 kg were used in the trial. The treatments arranged as a 2*2 factorial within a 4*4 Latin square were:

Age of cassava leaves:

Old versus young

            Type of palm oil

                        Refined versus crude

The four treatments were thus:

            YCPO: Young cassava leaves plus crude palm oil

            YRPO: Young cassava leaves plus refined palm oil

            OCPO: Old cassava leaves plus crude palm oil

            ORPO: Old cassava leaves plus refined palm oil

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 recording of feed refusals. The animals were housed in metabolism cages during the whole trial. The metabolism cages (80x80cm) were built to allow the quantitative collection of faeces and urine. The characteristic have been described elsewhere (Chiev Phiny and Rodriguez 2001). The metabolism cages were installed in an open stable.  

Characteristics of cassava leaves 

The old leaves were harvested from cassava grown for root production in farmers’ fields in Kandal province. The leaves were harvested when the plants were between 4.5 and 5 months old. The young leaves were harvested from a 2 month regrowth of cassava managed as a semi-perennial forage crop (Preston and Khieu Borin 2000) in the ecological farm of UTA. Both type of cassava leaves (after removing stems and petioles) were 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 containers tightly closed to prevent entry of air for 30 and 60 days for young and old leaves, respectively. Every container contained approximately 100 kg of fresh material. The chemical characteristics of both types of ensiled cassava leaves are listed in Table 1.  

 

Feeds and feeding system

The diets were formulated to contain 45% (in DM) of the two types of ensiled cassava leaves (Table 2) and 15% of either refined or crude oil from oil palm (Elaseis guineensis, Jacq), the remainder being broken rice and fishmeal. The refined oil originated from Malaysia; the crude oil was from the oil palm plantation in Cambodia (Mong Rethy Investment of Oil Palm of Cambodia). Broken rice and fish meal were purchased in the local market and were of Cambodian origin. A premix was purchased and added to all diets in recommended amounts according to NRC (1998).

The pigs were fed thrice daily with equal rations at 8:00 am, 12:00am and 3:00pm. The cassava leaf silages were offered mixed with the other components of the ration. Feed intake was programmed to be 47.0 and 45.0g DM/kg body weight for young and old cassava leaf silage, as it was observed that the silage made from old leaves appeared to be slightly less palatable than silage from young leaves. Water was permanently supplied through drinking nipples. The animals were weighed at the beginning of the trial and every ten days. Overall the daily working routine was the same as described by Chhay Ty et al (2003).

Data collection

Feed refusals and faeces were collected every day during the last 5 days of each period and were kept frozen in plastic bags until analysis.  At the end of every period, feed refusals and faeces were mixed thoroughly by hand, ground in a coffee grinder in the fresh state and, thereafter, representative samples were used for chemical analyses. Urine was collected in a plastic bucket to which a 10% solution of 4N sulphuric acid was added to maintain the pH below 4.0.   

Chemical analyses

Chemical analyses of the 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 and HCN. The DM content was determined using the microwave method of Undersander et al (1993). Fresh faeces were analyzed for pH according to a procedure described by Ly et al (2001a). The N content of urine was determined by the AOAC (1990) procedures. In vitro digestibility and water solubility of cassava leaf silage were determined by the methods described by Ly  and Preston (2001).

The gross energy of the feed ingredients, diets and faeces were 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 coefficient of 4.184 kjoule/kcal was used to convert kcal to joules.

Statistical analyses

The data were subjected to analysis of variance (ANOVA) using the General Linear Model (GLM) of the MINITAB software (Release 13.31, 2000). In the required cases means were separated by the Duncan’s multiple range test procedure (Steel and Torrie 1980). The model used was:

Y_{ij =} m + A_i + P _j +AP_ij  + e _ij    where  

 

Y_ij = Independent variable

m = overall mean

A_i = Effect of age of cassava leaves

P_j = Effect of type of palm oil

AP_ij  = Interaction of age of leaves*type of palm oil

e_ij = random error

 

Results

There were no health problems and the pigs gained weight during the experiment. Intake appeared to be slightly less for pigs given silage of old compared with young leaves and for crude palm oil compared with refined oil,  but the differences were not significant (Table 3).  

 

 

There was no significant dietary effect on pH of the faeces. Faecal DM content and material output was higher for silage from old cassava leaves compared with young ones, but there were no differences between crude and refined oil (Table 4).
 

 

There was no significant interaction (P>0.05) among digestibility indices between the age of the cassava leaves and the type of palm oil. There was a marked effect of cassava leaf maturity on nutrient digestibility (Table 5) favouring the silage prepared with young leaves.  The effect was more evident for DM, organic matter, crude fibre, ether extract, NFE and energy digestibility than for NDF digestibility. There was no effect of the type of palm oil on any nutrient digestibility index.

 

N digestibility was higher for young than for old cassava leaves (Table 6), and daily N retention (P=0.03) was higher also for the young compared with old leaves. Type of palm oil had no effect on N balance indices except for a trend to higher N intake with the refined oil (P=0.07).   

 

 

Silage made from young cassava leaves had a higher content of water soluble dry matter, organic matter and N than silage from old  cassava leaves. The same effect was found for in vitro (pepsin/pancreatin) values (Table 7).  Water holding capacity was higher for the silage made from old compared with the young leaves.

 

 

Figure 1: Comparison between in vitro digestibility and water solubility of DM
for silages made from young or old leaves 

 

Figure 2: Comparison between in vitro digestibility and water solubility of N
for silages made from young or old leaves  

Discussion

Young versus  old cassava leaves

Plant protein is mainly present as enzymes found in high concentration in the actively growing tissue.  The results in this study agree with the conclusions of Yao et al (2000), albeit with a different plant species,  who reported that mulberry leaves harvested in spring, when new re-growths are abundant, had superior nutritive value when compared to older leaves harvested in the autumn.

 

In a review of the literature concerning the use of ensiled cassava leaves as protein sources for growing pigs, Ly and Rodriguez (2001) contrasted the results of feeding ensiled cassava leaves in Cambodia, with similar studies carried out in Vietnam. They noted that digestibility and N retention were usually higher in the results reported from Cambodia and concluded that the explanation could be the fact that in Cambodia the leaves were always from young re-growths of cassava harvested as a perennial forage (Preston 2001), while in Vietnam they were usually the residues after harvesting the roots. Our results strongly support this hypothesis. 

 

As it is well known, NDF consists of cellulose, hemicellulose and lignin and can be regarded as a measure of the cell wall component. It is desirable that the concentration of NDF is low in diets to be fed to pigs due to the difficulty of cell wall digestion in monogastric animal species. Thus 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 digestibility of dry matter, crude protein, crude fibre, nitrogen free extract, organic matter and acid detergent fibre decreased with increasing levels of dietary wood pulp. The fact that the fibre and NDF fractions tended to be lower and were better digested in young rather than old cassava leaves, is in accordance with the report by Ravindran and Ravindran (1988), that with maturity, the fibrous fraction of cassava leaves changes its structure and composition. The superior nutritive value of young rather than old cassava leaves could be due to the effect of possible changes in the linkage of nutrients to the fibre fractions. Fernández and Jorgensen (1986) reported that a 1% unit increase of crude fibre depressed the digestion of protein by around 2% units. Le Thi Men (1999) also reported that the high fibre level of water spinach reduced the digestibility of protein for pigs

 

Faecal dry matter concentration decreased in the pigs fed silage from young cassava leaves as compared with silage from old cassava leaves, which may reflect the increase in microbial activity in the caecum and colon of pigs fed diets high in fibre (Jorgensen et al 1996).

 

Since the early report from Eggum (1970), it is well known that cassava leaves contain a relatively high proportion of lysine in the protein but a low proportion of methionine. The use of fish meal as a complementary protein source, rich in sulphur amino acids, could explain at least partially the good result in the present study.

 

The values of in vitro pepsin/pancreatin and water soluble dry matter, organic matter and N of the ensiled cassava leaves were similar to those reported by Ly and Samkol (2001), and reflected the differences in in vivo digestibility. Interestingly, values for water soluble N were similar to those obtained by the in vitro pepsin/pancreatin procedure.  The former is simpler and requires no chemicals and appears to be a good indicator of the protein digestibility.  

Type of palm oil

To the best of our knowledge, few studies, if any, have been performed to compare the nutritive value of refined and crude palm oil. A comparison of the nutritive value of the crude and refined palm oil used in the current study is not strictly valid,  since the refined palm oil was from the local market, and not from the Cambodia factory where the crude palm oil was obtained. Nevertheless, the evaluation of both types of palm oil did not reveal major differences between them them.

In temperate countries, where there is no availability of local crude palm oil, the use of refined palm oil used is logical. However, in palm oil producing countries and, amongst them Cambodia, the use of crude palm oil in pig feeding should be a very attractive nutritional strategy, in order to decrease the cost of feeding, if comparisons between both types of product reveal no major differences in the animal response. Several reports support this strategy (Ocampo 1994; González et al 1999; this experiment). Nevertheless, in some cases of experiments conducted in the lowland tropics it is very difficult to determine the type of palm oil that was used (eg: the experiment reported by Balogun and Fetuga 1984).

The fatty acid composition of refined and crude palm oil has been examined by Eekhout et al (1983). According to Eeckout et al (1983), palmitic and oleic acid are the two predominant fatty acids in both crude and refined palm oil (Table 8). In this connection, refined palm oil had a higher saturated fatty acid content than crude palm oil.  Nevertheless, Eeckhout et al (1983) reported a rather similar value for crude and refined palm oil digestibility in pigs of 73.1 and 75.9% respectively.  

According to the study of Chhayty et al (2003), the  digestibility of ether extract increased with level of palm oil (0 to 15%) in the diet containing 45% of cassava leaf silage but there was no influence of oil level on digestibility of other nutrients.

Conclusions

Diets with 45% of ensiled leaves from cassava managed as a semi-perennial forage with leaf harvest at 8 week intervals were digested better than diets with cassava leaves collected from mature (4 to 5 month old) cassava plants. There was a tendency for this difference to be reflected in higher values for N retention.

 

Water soluble dry matter and nitrogen were much higher for the silage made from the young compared with mature leaves of cassava, the differences being 30 and 50%, respectively.

 

There were no differences between diets due to the source of the palm oil (refined or crude).

 

Acknowledgements

The present experiment is a part of project directed to the study of the use of ensiled cassava leaves and palm oil in pigs, supported by the MEKARN project financed by Sida-SAREC, and was presented as partial requirement for the MSc degree at SLU, Uppsala, Sweden. The authors express their gratitude to all the personal of the Ecological Farm, from the University of Tropical Agriculture Foundation, for helping in assistance with the experiment. The authors thank Mr. Keo Saeth for his taking care of the pigs during the experiment. Thanks also to Mr. Pok Samkol for analytical assistance in the laboratories of the Ecological Farm.

  

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Received 15 June 2003; Accepted 8 August 2003

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