Digestibility and N-retention in crossbred pigs of diets with water spinach or water spinach mixed with mulberry leaves as protein sources in basal diets of cassava root meal plus rice bran, or sugar palm syrup plus broken rice

Chiv Phiny, B Ogle*, T R Preston** and Khieu Borin

Centre for Livestock and Agriculture Development, PO Box 2423, Phnom Penh 3, Cambodia
chphiny@celagrid.org  
^*Department of Animal Nutrition and Management, SLU
^**TOSOLY, UTA-Colombia, AA#48, Socorro, Santander, Colombia

Abstract

The aim of the study was to determine the digestibility and N retention in crossbred pigs fed water spinach or water spinach mixed with mulberry leaves, as protein sources in basal diets of cassava root meal (CR) plus rice bran (RB), or sugar palm syrup (SP) plus broken rice (BR). Eight castrated male crossbred pigs (Large White X Local breed) of average live weight 25 kg were used in the experiment. The design was a 2*2 factorial within duplicated 4*4 Latin squares with 12 days per period, 7 days for adaptation and 5 days for faeces and urine collection.

In the factorial analysis there were no significant interactions between energy and protein (leaves) sources in any of the measured traits. There were no differences due to source of energy for dry matter (DM) and crude protein (CP) intakes (P>0.05), but crude fibre (CF) intake was higher on the CRRB diet, reflecting the presence of the rice bran, which had a higher crude fibre content than all the other ingredients. Coefficients of apparent digestibility of DM, CP and CF were higher for the SPBR diets. The source of protein had no effect on either feed intake or apparent digestibility coefficients (P>0.05). However, when 50% of the water spinach was replaced by mulberry leaves, there were differences in N balance traits, with reduced N excretion in urine and higher N retention in absolute amounts and also in retained N as percentages of N intake and N digested. It is concluded that protein utilization efficiency is increased when the protein source is a mixture of water spinach and mulberry leaves rather than only water spinach.

Key words: Chemical analysis, crude fibre, crude protein, dry matter, faeces, urine

Introduction

In Cambodia, pigs are raised mainly to increase family income at village level and there are few commercial enterprises. The diets used by farmers 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. It has been shown recently that water spinach grown on poor sandy soil responds dramatically to fertilization with the effluent from a biodigester 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 (DM) with a crude protein (CP) content of 22% in the DM. Other reports indicate that the fresh leaves and stems of water spinach have a CP content of between 20 and 31% in DM (Le Thi Men et al 2000; Bui Huy Nhu Phuc 2000; Prak Kea 2003; Chhay Ty and Preston 2005) 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 also 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). The limitations in the use of water spinach in pig diets are likely to be its voluminous nature and relatively low digestibility. According to Ly et al (2002), in vitro digestibility of nitrogen is only 56%, compared with 75% in duckweed. The low energy density in water spinach can be corrected by supplementation or combination with energy-rich feeds, such as cassava root meal, rice bran, sugar palm syrup and broken rice.

Mulberry trees have been domesticated for many centuries for feeding silkworms (Tingzing et al 1988) and there are reports of their use in Cambodia for this purpose, but these activities have been developed only on a small scale (Delvert 1961). Mulberry leaves have been fed successfully to sheep and goats in Vietnam, and Vu Chi Cuong et al (2005) showed that for cattle, fresh mulberry leaves had the same protein value as cottonseed meal. Less is known about the nutritive potential of mulberry leaves for pigs. In a preliminary study in Cambodia (Chiv Phiny et al 2003), it was found that pigs showed a slight preference for fresh versus sun-dried leaves; however, a more interesting finding was that the DM digestibility of the diet increased linearly (R²=0.86) with increasing proportions of mulberry leaves (range of 0 to 50% mulberry leaves in the diet DM). From these data (Y = 0.131X + 75.9, where Y is % DM digestibility and X = proportion (%) of mulberry leaves in the diet DM), it can be predicted that with 100% mulberry leaves in the diet, the DM digestibility would be 89%.

The bulky nature of vegetative protein sources such as mulberry leaves and water spinach could be a factor limiting their intake by pigs. Thus there are likely to be advantages if the energy source is low in fibre. For this reason the energy source in the diets used by Le Thi Men and Bui Hong Van, (1993) was reconstituted sugar cane juice, which contains no fibre. In Cambodia, the use of syrup from sugar palm (Borassus flabellifer) as the energy source for pigs could be an interesting possibility for the small-scale farmer. Encouraging results were reported with sugar palm syrup supplemented with soya bean meal (Khieu Borin et al 1996). However, there are no reports on the use of protein-rich leaves as the protein supplement in diets of palm syrup plus broken rice.

Cassava root meal is low in both fibre and in protein, making the economic utilization of the roots in animal feeds highly dependent on the incorporation of other protein-rich ingredients (Balagopalan et al 1988). According to Preston and Murgueitio (1992), the low protein content of most tropical feeds that could be used as basal diets in pig and poultry feeding requires that almost all the dietary needs for amino acids must be supplied as an addition to the basal diet. However, there are no reports on the use of cassava root meal plus rice bran with the protein-rich leaves as the protein supplement in pig diets.

The hypotheses to be tested were that apparent digestibility coefficients of DM, CP and CF, and efficiency of protein utilization, would be higher: (i) when the energy component of the diet was low in fibre; and (ii) protein utilization would be improved when the protein was derived from a mixture of mulberry leaves with water spinach rather than water spinach alone.

Comparisons of fibre level were made by comparing a mixture of cassava root meal plus rice bran with sugar palm juice and broken rice. The protein sources were fresh water spinach alone or combined 50:50 (DM basis) with fresh leaves of mulberry.

Materials and methods

Location and climate

The experiment was carried out from November 15 to December 28, 2006, in the Ecological farm of the Center for Livestock and Agriculture Development, CelAgrid- Cambodia, located in Prah Theat village, Rolous Commune, Kandal Steung District, Kandal Province, near Phnom Penh City. The ambient temperature was about 35^oC in the middle of the day.

Experimental design and treatments

Eight castrated male crossbred pigs (Large White X Local breed) of average live weight 25kg were allocated to a 2*2 factorial arrangement within a replicated 4*4 Latin square design (Table 1).

The factors were:

• Energy source: Cassava root meal plus rice bran or sugar palm syrup plus broken rice
• Protein source: Water spinach or a 50:50 mixture of water spinach and mulberry leaves

The individual treatments were:

• WCRRB: Water spinach with cassava root meal plus rice bran
• WSPBR: Water spinach with sugar palm syrup plus broken rice
• WMCRRB: Mixture of water spinach and mulberry leaves (50: 50 DM basis) with cassava root meal plus rice bran
• WMSPBR: Mixture of water spinach and mulberry leaves (50: 50 DM basis) with sugar palm syrup plus broken rice

In each Latin square there were 4 periods each of 12 days, 7 days for adaptation and 5 days for faeces and urine collection.

The chemical composition of the dietary ingredients is shown in Table 2, and the ingredient and chemical composition of the experimental diets in Table 3.

Experimental feeds and feeding

Water spinach was purchased daily in the local market, but cassava root meal, rice bran, broken rice and sugar palm syrup were bought every week, also in the local market. Mulberry leaves were harvested in the CelAgrid ecological farm. Water spinach and mulberry leaves were chopped into 0.5-1cm pieces and mixed with cassava root meal plus rice bran or sugar palm syrup plus broken rice before feeding to the pigs. A premix of minerals, vitamins and salt was also added to the diets. The protein level was limited to 13% CP in the DM of all diets. The composition of these feeds (Table 2) is calculated from analytical data of the ingredients, which were analyzed in the CelAgrid laboratory. The proportions in each of the diets are shown in Table 3 (DM basis). All the ingredients were mixed together. The total amount fed was fixed at 80% of the ad libitum intake observed during the adaptation period. The pigs were fed three times per day, at 07.00, 12.00 and 16.00h.

Animals and housing

The pigs were housed in metabolism cages made from rattan and bamboo strips fixed to a wooden frame in a composite unit (1.6 m length and 0.8 m wide) for 2 pigs per unit (Photo 1). The metabolism cages allowed the pigs to move freely. The cages were fitted with automatic water drinkers. The floor area of each metabolism cage was 80 x 80cm and was designed to make it possible to collect the faeces and urine separately. 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. A solution of 10% of H₂SO₄ was added to maintain the pH of the urine below 4 during the collection periods.

Data collection

Faeces was collected and weighed every day, and then were kept frozen in plastic bags until analysis. At the end of each period, feed refusals and faeces were mixed thoroughly by hand and homogenized in a coffee grinder prior to analysis. Urine was collected in plastic buckets. At the end of each period the volume was measured and samples taken for analysis. The animals were weighed at the beginning of the trial and every 12 days.

Chemical analysis

Chemical analysis 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 and crude fibre. 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 AOAC (1990) procedures. All the analyses were done in duplicate. Amino acid analyses were carried out by AnalCen Nordic AB (Sweden) (Table 4).

Statistical analysis

The data were analyzed using the general linear model option of Minitab ANOVA software (Minitab release 31.31, 2000). The model used was:

Y_ijkl= μ + E_i + L_j + E_i*L_j + A_k + P_{l +} e_ijkl

where:

Y = Dependent variable,
μ = Overall mean,
E_i = Energy effect,
L_{k =} Leaves effect,
E_i*L_j = Interaction Energy*Leaves,
A_k = Animal effect,
P_l = Period effect,
e_ijkl = Random error

Results

In the factorial analysis there were no significant interactions between energy and protein (leaves) sources in any of the measured traits. The results for feed intake, apparent digestibility and N balance are therefore presented as main effects (Table 5).

The pigs were in good health and gained in live weight during the trial. There were no symptoms or signals of discomfort from the consumption of the diets.

Effect of energy source

There were no differences due to source of energy for DM and crude protein intakes, but crude fibre intake was higher on the CRRB diet (Table 6), reflecting the presence of the rice bran which had a higher crude fibre content than all the other ingredients (Table 6). The DM content of the faeces was lower for pigs fed the SPBR diet (Table 7) indicating a faster rate of passage of digesta. Coefficients of apparent digestibility of DM, crude protein and crude fibre were higher for the SPBR diets, probably because of the lower content of crude fibre (Table 8 and Figures 1 and 2).

Figure 1.  Mean values for apparent digestibility of DM in pigs fed cassava root meal plus rice bran [CRRB] or sugar palm syrup plus broken rice [SBBR] with water spinach or water spinach + mulberry leaves	Figure 2.  Mean values for apparent digestibility of crude protein in pigs fed cassava root meal plus rice bran [CRRB] or sugar palm syrup plus broken rice [SBBR] with water spinach or water spinach + mulberry leaves

Effect of protein source

The source of protein had no effect on either feed intake (Table 6) or apparent digestibility coefficients (Table 8; Figures 1 and 2). However, there were differences in N balance traits, with reduced N excretion in urine and higher N retention in absolute amounts and also in retained N as percentages of N intake and N digested (Table 9 and Figures 3 and 4), when 50% of the water spinach was replaced by mulberry leaves.

Discussion

The higher values of the apparent digestibility coefficients for dry matter, crude protein and crude fibre when the energy source was sugar palm syrup and broken rice rather than cassava root meal and rice bran, are in accordance with the first hypothesis concerning the expected effects of a lower level of fibre in the diet. Chhay Ty and Preston (2005) recorded higher growth rates when broken rice was compared with a mixture of cassava root meal and rice bran. However, there were not the expected benefits from lower fibre levels on N retention, which in the present experiment did not reflect differences in dietary fibre content.

The finding of increased urinary N loss and decreased N retention (as percentage of N intake and of digested N), when the proportion of water spinach in the diet was increased, was similar to effects noted by Chhay Ty and Preston (2005b) in an experiment where water spinach was increased from 17 to 47% of the diet DM. Chittavong Malavanh and Preston (2006) also observed decreased efficiency of utilization of dietary N (increase in urinary N and lower N retention) in growing pigs, as a result of increasing the proportion of water spinach replacing the fresh leaves of sweet potato. These two reports and the findings of the present experiment provide support for the first hypothesis that high levels of water spinach in the diet lead to increased losses of N in urine and poorer N retention. Chhay Ty and Preston (2006) found that high levels of water spinach (more than 30% of diet DM), replacing fresh cassava leaves, reduced the growth rate of pigs, probably also as a result of the diuretic effect of water spinach. The significantly higher N retention in the diets when the protein was supplied as a mixture of mulberry leaves and water spinach, compared with water spinach alone, could also in theory have been partly a result of the superior protein quality of the foliage mixture. However, although mulberry contains somewhat higher concentrations of lysine, methionine plus cystine and threonine than water spinach, the levels of these amino acids as a proportion of the lysine are similar in both feeds, and closely resemble the ideal protein, and so differences in the amino acid balance between the foliage mixture and water spinach alone can not explain the differences in N-retention.

Conclusions

• When energy sources with low concentrations of crude protein (combinations of cassava root meal with rice bran or sugar palm syrup with broken rice) are used in pig diets, it is possible to provide all the supplementary crude protein from vegetative sources such as water spinach and mulberry leaves.

• Protein utilization efficiency was increased when the protein source is a mixture of water spinach and mulberry leaves rather than only water spinach.

Acknowledgements

The authors wish to thank the MEKARN project, financed by Sida/SAREC for supporting this research. Thanks are also given to the staff of CelAgrid for assistance during the entire experiment, especially Mr Oum Sitha, Seng Theara and Seun Brosfor taking care of the feeding and management of the pigs. Thanks are also expressed to Mr Chhay Ty and Pek Samnang for assistance in helping to analyze the samples in the laboratory.
 

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