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Twenty four crossbred (Local*Landrace or Local*Duroc) castrated male pigs weighing from 16.0 to 18.4 kg were used in a 2*3 factorial arrangement to study the effect of (i) different levels of substitution of wilted cassava leaves by water spinach; and (ii) a basal diet of broken rice or a mixture (50:50) of rice bran and cassava root meal. The feeding trial lasted for 120 days from 8 August to 6 December 2005. Higher intakes of water spinach and cassava leaves, and of total DM, were observed when the basal diet was broken rice rather than rice bran mixed with cassava root meal. Increasing the replacement of cassava leaves by water spinach from 10 to 30% resulted in increases in intake of the energy component, in the total quantity of foliage, and of total DM. Growth rates tended to be higher on the broken rice diet than on rice bran and cassava root meal; while the 30% level of water spinach was superior to the 10% level. The overall trend of live weight gain as a function of level of water spinach was curvilinear and positive, indicating a synergistic effect on performance from mixing increasing amounts of water spinach with fresh cassava leaves.

Key words: cassava leaves, growth, broken rice, cassava root meal, rice bran, pigs, protein, water spinach

Introduction

In a previous experiment (Chhay Ty and Preston 2005) with growing pigs fed a basal diet of broken rice, we showed that a supplement of a 50:50 mixture (DM basis) of water spinach ( Ipomoea aquatica ) and fresh cassava leaves ( Manihot esculenta ) supported growth rates that were 32% higher than the average of the growth rates on the two sources of foliages fed separately. In the present experiment the hypothesis to be tested was that lower proportions of water spinach would also have a synergistic effect on growth of pigs fed low protein basal diets.

Materials and methods

Location

The experiment was carried out from 8 August to 6 December 2005 in the Center for Livestock and Agriculture Development (CelAgrid-UTA Cambodia), located in Kandal village, Rolous Commune, Kandal Steung district, Kandal province, about 25km from Phnom Penh City, Cambodia .

Experimental animals, treatments and design

Twenty four crossbred (Local*Landrace or Local*Duroc) castrated male pigs with initial body weight from 16 to 18.4 kg were allocated to six treatments with 4 replicates per treatment in a 2*3 factorial arrangement. The factors were:

Energy

• Broken rice
• Cassava root meal mixed with rice bran

Protein supplement

Proportions of water spinach (WS) and fresh cassava leaves (FCL) in ratios (DM basis) of:

• WS 10% and FCL 90%
• WS 20% and FCL 80%
• WS 30% and FCL 70%

The pigs were allocated into 2 blocks according to live weight (means for each block were 14.6 and 20.3 kg). The nutritional treatments were applied at random within each block. The pigs were housed in individual pens with concrete floors and provided with feeders and drinking nipples. The pigs were vaccinated against Salmonella disease and were adapted to the feeds and the housing for 7 days before starting the experiment.

Feeding and management

Broken rice and rice bran are by-products of Cambodian rice mills and were available in the local area. Cassava root meal was purchased from a store in the city. Fresh cassava leaves were harvested every day from plots in CelAgrid (Photo 1) or they were purchased from a farmer near the center. The water spinach was purchased from traders who harvested it from lagoons receiving waste water from Phnom Penh city.

The leaves plus stems of the water spinach and the leaves of cassava (after removing stems and petioles) were chopped into small pieces and wilted over-night and then mixed with the other ingredients of the diet (Tables 1 and 2) before being offered in 3 meals at 8.00, 12.00 and 17.00h. The amounts of feeds offered were based on the allowance of 40 g DM per 1 kg live weight of the pigs, with the broken rice (or mixture of rice bran and cassava root meal) supplying 50% and the mixtures of leaves providing the remainder.

Data collection and analyses

The pigs were weighed every 10 days during the trial which lasted 120 days. Individual feeds offered and residues were recorded daily. Samples of feeds and residues were analysed for DM, N and HCN. The DM content was determined using the micro-wave method of Undersander et al (1993). N and HCN were determined following procedures of AOAC (1990).

Statistical analysis

Data for weight gain, DM feed intake, crude protein intake, HCN intake and feed conversion rate were analysed using the general linear model (GLM) option of the ANOVA software of Minitab (2000). The sources of variation were blocks, level of water spinach, energy, interaction energy*level of water spinach and error.

Results and discussion

Feed intake

Higher intakes of water spinach and cassava leaves were observed when the basal diet was broken rice rather than rice bran mixed with cassava root meal (Table 3), with total DM intakes being higher for the latter when expressed on a live weight basis. Replacing cassava leaves with water spinach resulted in increases in intake of the energy component, and in the total quantity of foliage, but a decrease in the intake of cassava leaves (Figures 1 and 2).

Table 3 : Mean values (main effects) for feed intake of pigs fed broken rice or rice bran + cassava root meal supplemented with mixtures of fresh cassava leaves and fresh water spinach

On a live weight basis the HCN levels consumed were 4.99, 4.1 and 2.86 mg/kg LW, for the water spinach 10, 20 and 30% levels, respectively. These were lower than in the earlier study (Chhayty et al 2005) and in the range reported as potentially toxic: 1.4 by Getter and Baine (1938), 2.1 to 2.3 by Johnson and Ramond (1965), 3.5 by Tewe (1992) and 4.4% of LW by Butler (1973).

Growth and feed conversion

Growth rates tended to be higher on the broken rice diet than on rice bran and cassava root meal during the initial, final and overall trial period. For the periods 40 to 80, 80 to 120 and overall, the 30% level of water spinach was superior to the 10% level.

Table 4 : Mean values for initial and final live weights, and growth rates, of pigs fed broken rice or a mixture of rice bran and cassava root meal supplemented with different levels of water spinach replacing fresh cassava leaves

The overall trend of live weight gain as a function of level of water spinach was curvilinear and positive (Figures 6 and 7), indicating that the rate of increase in live weight gain by replacing cassava leaves with water spinach was more marked the higher the level of water spinach in the diet. The growth curves in Figures 2 and 3 indicate a similar trend.

Feed conversion was better on the basal diet of broken rice than on the mixture of rice bran and cassava root meal and tended to improve (P=0.12 for the overall trial period) with increasing levels of water spinach (Table 5).

Table 5 : Mean values for DM feed conversion of pigs fed broken rice or a mixture of rice bran and cassava root meal supplemented with different levels of water spinach replacing fresh cassava leaves

Conclusions

• The synergistic effect on growth rate of pigs of replacing cassava leaves with water spinach, as the main protein source, was confirmed in that the relative response to substituting cassava leaves with water spinach increased as the degree of replacement was increased.
• There were no indications of HCN toxicity on any of the diets

Acknowledgments

The authors would like to express their gratitude to the MEKARN project financed by the SIDA-SAREC Agency, and to the Center for Livestock and Agriculture Development (CelAgrid UTA-Cambodia), for providing resources for conducting this experiment

References

1. AOAC 1990 Official Methods of Analysis. Association of Official Analytical Chemists. 15th Edition (K Helrick editor). Arlington pp 1230
2. Butler G W 1973 Physiological and genetic aspects of cyanogenesis in cassava and other plants, Chronic cassava toxicity. Proceedings of the Interdisciplinary Workshop, London England, 29-30 Jan., 1973. IDRC -010e, pp. 65-71
3. Chhay Ty and Preston T R 2005 Effect of water spinach and fresh cassava leaves on intake, digestibility and N retention in growing pigs. Livestock Research for Rural Development.Vol. 17, Art. #23. Retrieved printDate() June 30, 2005, from http://www.cipav.org.co/lrrd/lrrd17/2/chha17023.htm
4. Getter A O and Baine J 1938 Research on cyanide detoxification. American Journal of Medical Science. pp. 185-189
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8. UndersanderD, Mertens D R and Theix N 1993 Forage analysis procedures.National Forage Testing Association. Omaha pp15

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