Feed intake, digestibility and N retention of a diet of water spinach supplemented with palm oil and / or broken rice and dried fish for growing pigs

Prak Kea, T R Preston^* and  J Ly**

Royal University of Agriculture,
Faculty of Animal Science and Veterinary Medicine

prakkea@yahoo.com / prakkea@hotmail.com

* University of Tropical Agriculture Foundation
Chamcar Daung, PO Box 2423, Phnom Penh 3, Cambodia

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

Abstract

 

The experiment was conducted at UTA (University of Tropical Agriculture, campus of the Royal University of Agriculture, Kingdom of Cambodia) where the annual temperature ranges from 26 to 31°C. The aim of the study was to determine the effect of different ratios of palm oil and broken rice on the intake, apparent digestibility and nitrogen retention by crossbred pigs of diets based on fresh water spinach (WS) supplemented with fish meal. Four castrated crossbred male piglets of 8-10 kg initial live weight were used in the trials. They were housed in individual cages and allocated to four treatments according to a 4 * 4 Latin square arrangement. The treatments were four diets in which water spinach was progressively substituted by 0, 5, 10 and 15% of palm oil. The diets were supplemented with fish meal to contain 15 % crude protein (Nx6.25).

The dry matter feed intake as a percentage of DM offered, and the apparent digestibilities of dry matter and organic matter decreased, as the proportion of palm oil increased. Level of palm oil had no effect on digestibility of crude fiber and N, nor on N retention.

It is concluded that fresh water spinach can provide up to 70% of the dietary protein for growing pigs, when it is supplemented with broken rice and up to 15% of palm oil.  

 Key words: Digestibility, nitrogen balance, palm oil, pigs, water spinach

  

Introduction

Cambodia is one of the poorest developing countries in the world. The country covers 181, 035 km² and has a population of over 11 million. The economy is based mainly on agriculture, of which rice production is ranked in the first place. Almost all of the people are farmers. Nearly 90% of the population earn their living in the agricultural sector in a crop-livestock production system dominated by smallholder farmers. Almost all farmers keep livestock; usually pigs, chickens, fish, cows and buffaloes. Cattle and buffaloes are kept mainly for draught power purposes, both for land preparation and transport. Pigs are raised mainly to increase family income at village level and there are few commercial enterprises.

The productivity of livestock is low as inputs such as labour, feed resources and other investments are also low. Nevertheless, monogastric animals play an important role in agricultural activities and meat production. On average, a farmer will hold 2 to 5 heads of pigs of the local breed or crossbreed between local and exotic breeds. As in other developing countries in the region, monogastric animals, particularly pigs, rely mainly on rice bran with addition of other crop by-products. The major problem in pig production is the lack of adequate feed because feed resources are scarce and, if available, the prices are prohibitive.

Most of the available feed resources have low digestibility and are low in protein and minerals, which results in low levels of performance. The need therefore is to identity feeds which can compensate for these deficiencies. Water spinach (Ipomoea aquatica) is a water and marsh plant with creeping, hollow, water filled stems and shiny green leaves. It is cultivated for human food and used as pig and other animal feed in Cambodia  and throughout Southeast Asia. The fresh leaves and stems of water spinach have a crude protein content of between 20 and 31% in DM  (Le Thi Men et al 2000; Bui Huy Nhu Phuc 2000) and ash concentrations of around 12% of DM (Göhl 1981; Bui Huy Nhu Phuc 2000). Water spinach is readily eaten by pigs and is a locally available feed resource throughout the country. It has been used successfully to replace part of the protein in a diet of sugar cane juice for breeding sows in Vietnam (Le Thi Men and Bui Hong Van 1993).

It has been shown recently that water spinach grown on poor sandy soil responds dramatically to fertilization with the effluent from biodigestors charged with pig manure (Kean Sophea and Preston 2001). Yields of up to 24 tonnes of fresh biomass/ha were achieved in a growth period of only 30 days from the time of sowing the seed. The fresh biomass contained 10% dry matter with a protein content of 22% in the dry matter. On an annual basis this represents of the order of 20 to 25 tonnes of dry matter/ha with 4 to 6 tonnes/ha of protein. This high yield potential enables many farmers to get a regular high income from harvesting water spinach and selling it in local markets.

The limitation to the use of water spinach in pig diets is likely to be its voluminous nature and relatively low digestibility. According to Ly et al (2002), the in vitro digestibility of the nitrogen is only 56% compared with 75% in duckweed. The low energy density in water spinach is another limitation and could be corrected by supplementation with energy-rich vegetable oils such as palm oil. The protein in water spinach, as in other plant proteins, is deficient in sulphur amino acids, thus dried fresh water fish, available locally in Cambodia, would be a logical supplement to complement the protein in water spinach.

The use of African palm (Elaeis guineensis) oil and its by products as a cereal grain replacement in pig production is a recent development of importance for tropical countries (Ocampo et al 1990a,b; Ocampo 1994a,b). In earlier experiments with palm oil the level in the diet was relatively low (less than 10%) and it was mixed with traditional ingredients (Balogun et al 1983; Abu et al 1984). By contrast, recent research has shown that the oil-rich fibrous by-product (Ocampo et al 1990a,b), the oil itself (Ocampo 1994a) or even the whole fruit (Ocampo 1994b) can be the basic component of the diet with oil levels reaching as high as 50% of the dry diet matter, and that growth and carcass traits are of the same order as in pigs fed diets based on cereal grain. Observations by Ocampo (1994b) indicated that in diets composed mainly of fibre and oil (as in the case of the whole fruit of the oil palm) there are advantages in including a small proportion of carbohydrate in the diet in the form of rice polishings. In Cambodia, the polishings are included along with the bran in a single product.  Broken rice which has a much lower content of fibre would seem to be a more suitable source of carbohydrate for conditions in Cambodia.

Chiev Phiny and Rodríguez (2001) and Khieu Borin et al (1997) reported that fresh water fish and broken rice are abundant in Cambodia. The Tonle Sap Lake is thought to supply about 70% of the protein consumed by the 10 million inhabitants. The lake was reported in 1990 to occupy an area of 460,000 ha. It is one of the richest inland fishing lakes in the world and is considered to be nearly 10 times as productive as the best fishing grounds in the North Atlantic, with fish yields of at least 65kg/ha, calculated on the basis of the dry season area of the lake. Fishing activities start when the water flows out from the lake into the sea and Tonle Sap river at the beginning of the dry season (December-March). There are two occasions, in January and February, when especially large quantities of fish are harvested along the Tonle Sap river. It is traditional practice to sun-dry the small fish that are harvested at this time and to sell the product to farmers as a protein supplement for pigs and chicken. 

The aims of the study

The aim of the study was to determine the effect of different ratios of palm oil and broken rice on intake, apparent digestibility and nitrogen retention by crossbred pigs of diets based on fresh water spinach (WS) supplemented with dried whole fish. The hypothesis to be tested is that there will be benefits in animal performance from a combination of palm oil and broken rice, compared with broken rice alone, when water spinach is used to supply the major part of the protein in the diet.

 

Materials and methods   

Location 

The experiment was carried out from May to June, 2002 in the Ecological Farm of the University of Tropical Agriculture (UTA), located on the campus of the Royal University of Agriculture, Chamcar Daung, Kva village, about 12 km from Phnom Penh. The average annual temperature in this location is in the range of 26 to 31°C.

Treatments and design

Four crossbred castrated male pigs of average weight 9.5 kg were allocated to 4 dietary treatments (levels of palm oil of 0 [po0], 5 [po5], 10 [po10] and 15% [po15]), according to a 4*4 Latin square arrangement with 4 periods each of 10 days, 5 for adaptation and 5 for collection of faeces and urine. The allocation of the pigs to the diets is shown in Table 1.

 Diets

The chemical characteristics of the ingredients in the diets are shown in Table 2.

 

The daily dry matter (DM) allowance was calculated at 5% of the body weight and was divided between the water spinach and the dry supplements according to the composition data in Table 3. The water spinach was purchased daily in the local market and was chopped into small pieces prior to offering it in one of two feed troughs; the other feed trough was used for the dry components (supplements) of the diet which were mixed before feeding. The daily allowances of the supplements were weighed and put in small polyethylene bags (2 kg capacity) in sufficient numbers for each 10-day experimental period. The pigs  were fed twice daily, first at 7 am and then in the afternoon at 4 pm. The water spinach was offered after the pigs had consumed the supplements. Water was offered ad libitum through the automatic drinking nipples.

Animals and housing

The pigs were penned in metabolism cages made from rattan and bamboos strips fixed to a wooden frame in a composite unit (1.6m length and 0.7m wide) for 2 animals per unit (Photo 1).  The metabolism cages allowed the pigs to move freely. The cages were fitted with automatic water drinkers. Plastic netting was suspended below the floor to collect the faeces. The urine passed through the plastic net and was collected over a sheet of polyethylene leading to a filter placed in a funnel suspended over a plastic bucket containing sulphuric acid (10 ml of 4N acid) so as to maintain the pH below 4.0. The floor area of each metabolism cage was 80*80 cm. 

Photo 1: The metabolism cage made from rattan for measuring digestibility and N retention

 

Digestibility and N retention

During the 5-day collection period, the faeces were collected daily just before each morning feeding and kept in polyethylene bags at -20 ^oC. The total volume of urine was recorded daily and 10% of the total collection for each day was kept in plastic containers at -20 ^oC until the end of the experiment. At the end of the collection period the faeces were thawed and mixed thoroughly to provide a representative sample for each pig.

The pigs were weighed at the beginning of the experiment and then every 10 days. The feed refused was weighed and recorded daily and a sample was kept for analysis.  

Laboratory analyses

Dry matter, nitrogen and crude fibre were determined in feed offered and refused and in faeces. The urine was analysed for N. The chemical analyses were done following standard procedures according to the Association of Official Analytical Chemists (AOAC 1988), except for DM which was determined by micro-wave radiation (Undersander et al 1993).  The NDF was determined according to Van Soest et al (1991). 

Statistical analysis

The data for feed intake, apparent digestibility and N balance were subjected to analysis of variance according to the general linear model of the Minitab software (Minitab release 12.21, 1998). The model was:

Yi = μ + di + pi + ai + ei

 

Where Y = the dependent variable

μ = the overall mean

d = the effect of diet

p = effect of period

a = effect of animal

e = the residual error 

 

Results

In one of the pigs there were symptoms of diarrhea (loose faeces) during the two week period of adaptation to the cages before starting the experiment, apparently caused by the consumption of water spinach and oil. Subsequently the health of all animals was good. The values for dry matter, organic matter and crude protein of water spinach (Table 2) were similar to those in other reports (Bui Huy Nhu Phuc 2000; Le Thi Men et al 2000; Bruemmer and Roe 1979; Bun Tean et al 2002; Ly et al 2002). Feed intake was depressed slightly by addition of palm oil, especially at the 15% level (Table 4). This contrasts with the data of Chhayty et al (2003) where there were no effects of palm oil levels (0 to 15%) on feed intake.

 

There was an indication that the DM content of the faeces and fresh and dry faecal output were increased by including palm oil in the diet (Table 5). The values for faecal DM content were considerably lower than was reported by Chhayty et al (2003) for diets of ensiled cassava leaves supplemented with palm oil (range of 40 to 46%). Presumably this reflected the higher digestibility of the water spinach compared with ensiled cassava leaves, which in turn would be expected to increase the rate of passage of digesta and therefore less time for the absorption of water.

 

Apparent digestibility of DM and OM decreased as the level of palm oil was increased (Table 6).  The value for both these parameters on the control diet (zero palm oil) (89% for DM digestibility, and 90% for OM digestibility), were similar to those reported by Le Thi Men et al (2000) (range of 88.5 to 90.2 for digestibility of DM for diets with increasing levels of chopped water spinach), and were higher than those reported for diets in which similar levels of palm oil were added to a basal diet with 45% (in DM) of ensiled cassava leaves (71.2; 83.3%, respectively) (Chhaty et al 2003).  Ash digestibility was also depressed by increasing levels of palm oil.  Crude fiber digestibility was relatively high and not affected by palm oil inclusion in the diet.

 

The addition of palm oil to the diet based on water spinach had no effect on digestibility of N nor on N retention  (Table 7).

 

Discussion

There appear to be no reports in the literature on the effects of palm oil on the digestibility of a diet based on high levels of fresh water spinach. On a basal diet of ensiled cassava leaves, addition of palm oil at up to 15% of the DM, also reduced the digestibility of DM and OM digestibility in the work of Chhay Ty et al (2003).  The overall higher values for digestibility of DM and OM in this study compared with those reported by Chhay Ty et al (2003) presumably reflected the higher digestibility of water spinach compared with ensiled cassava leaves.

Since the early work of Low et al (1976), it is known that faecal ash digestibility can vary over a wide range of values, from 47 to 74%, according to the nature of the diet. Pallauf and Huter (1993) reported a range of 55.3 to 61.6% for ash digestibility in piglets weighing 10 kg.  Partridge (1978a) observed a range of 33 to 75% for calcium digestibility in growing pigs fed on a variety of diets.

Several factors can influence ash and calcium digestibility in pigs (Faliu et al 1971; Collings et al 1979; Helander et al 1994; Kemme et al 1997; Larsen et al 1999). In this connection, it has been suggested that some major proximal components of the pig’s diet such as cell wall constituents and ether extract (Partridge 1978b; Molnar and Thole 1987; Dintzis et al 1995) can be mineral sinks. Furthermore, the cell wall effect has been attributed to the cation exchange capacity of certain insoluble polysaccharides in the pig gut lumen (Partridge 1978b) whereas the ether extract effect was interpreted as a consequence of the enhanced reaction of calcium with fatty acids (Molnar and Thole 1987; Pallauf and Huter 1993). It is well known that a major part of the total lipid content of faeces is largely saponified in nature. Therefore, The results from the current study are supported by previous observations of Jorgensen et al (1983) who found that by increasing the level of dietary minerals, there was a consequent reduction in crude fat digestibility, indicating a binding of fat by the minerals.

In the current study, the crude fibre concentration was similar in all diets examined. However, the increasing amounts of  palm oil included in the diets could favour the formation of fatty acid salts, thereby depressing calcium absorption in particular and ash digestibility in general. This hypothesis needs to be supported by more experimental evidence.

Very little is known concerning the influence of the introduction of graded levels of palm oil on nutrient digestibility in pigs. In this connection, a slight decrease in ileal DM digestibility but not in ileal N digestibility has been observed in pigs fed up to 20% palm oil in the diet (Albin et al 2001). On the other hand, when palm oil was increased from 3.0 to 9.7% in the diet of weanling pigs, total N digestibility and retention was depressed in a Nigerian experiment (Balogun and Fetuga 1984). The use of 0, 5 and 10% of palm oil was studied by Gonzalez et al (1999) in Venezuela, with diets based on cassava foliage meal for growing pigs. In this study, it was observed that NDF digestibility decreased and ether extract digestibility was enhanced with increasing levels of dietary palm oil. However, there was no treatment effect on DM, organic matter and N digestibility.

The data showing no effect of the level of palm oil  on digestibility of N nor on N retention (Table 7) agree with the report by Chhay Ty et al (2003) where there was no effect of the palm oil on these parameters in diets based on ensiled cassava leaves. The range of values for N retention in this study (4.4 to 5.4 g/day) were lower than in the report of Chhay Ty et al (2003) (range of 7.2 to 8.00 g/day), which appeared to be due to higher N intake on the ensiled cassava leaf diet (13 to 14.7 g/day) compared with the diets in the present experiment (8.2 to 9.7 g/day). Another report concerning the use of palm oil in diets based on cassava leaves indicated no dietary influence on N balance of the pigs (Gonzalez et al 1999).

 

 Conclusions

On the basis of the findings in the present experiment there would appear to be no benefits from using palm oil to increase the energy density of a basal diet of fresh water spinach fed to growing pigs.

Acknowledgements

 The authors wish to thank the MEKARN project, financed by sida/SAREC for supporting this reseearch. The senior author expresses  gratitude to Dr T R Preston, Director of the University of Tropical Agriculture (UTA), for patient guidance and encouragement and allowing the use of the ecological farm and laboratory facilities throughout this study. Thanks are also given to the staff of the University of Tropical Agriculture Foundation for assistance during the entire experment, especially Mr Phin Phoung for taking care of the feeding and management of the pigs.  Dr. Julio Ly provided valuable assistance in helping to analyse the data and in the correction of the thesis. This research was submitted by the senior author as partial requirement for the MSc degree of Swedish University of Agricultural Sciences, Uppsala.

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Received 30 May 2003; Accepted 8 August 2003