Taro (Colocacia esculenta) silage and water spinach as supplements to rice bran for growing pigs

Nguyen Tuyet Giang

An Giang University (AGU)
Angiang Province, Vietnam
ntgiang@agu.edu.vn

Abstract

Three crossbred pigs (mean initial weight: 12.3 kg) were allocated to 3 treatments according to a 3*3 Latin Square design. The treatments were three supplements to a basal diet of rice bran:  water spinach (Ipomonea aquatica) only (WS), Taro (Colocasia esculenta ) silage only (TS) and mixture of water spinach and Taro silage (WS-TS). The trial was conducted in the experimental area of Kampong Cham National School of Agriculture in Kampong Cham province, Cambodia. The duration of the experiment was 42 days, from August 04 to September 16, 2008.

There were no differences in intake and apparent digestibility of DM and crude protein among the three treatments.  When only the diets containing water spinach  (diets WS and WS-TS only) were considered, there were significant relationships between  N retention and N retention as % of digested N and daily intake of water spinach.  By contrast, there were no relationships between taro silage intake and the retention of N for diets WS-TS and TS.  The implication from these contrasting results is that the biological value of the water spinach protein may be higher than that of the protein in the ensiled taro leaves and stems.

Overall, it can be concluded that Taro silage mixed with water spinach is a good source of protein for feeding to growing pigs as the apparent digestibility of crude protein (>80%) and the N retention as percentage of N digested (70.5%) were high on the mixed diets.

Key words: Digestibility, diuretic effect, Latin Square design, nitrogen utilization,

Introduction

Livestock production makes an important contribution to global food supply. We also have to cope with the considerable and increasing demand of finding new feed sources for animals. Many recent researches have been conducted with the purpose of utilizing the local feed resources and by-products of agriculture.

Water spinach (Ipomonea aquatica) can grow easily not only in soil but also in water (pond or river). It is planted traditionally for human consumption in South East Asia and appears to be devoid of non-nutritional elements (Chittavong Malavanh 2006). Within a growth period of only 30 days from the time of planting the seed, the yield of water spinach was up to 24 tones of fresh biomass/ha (Kean Sophea and Preston 2001). The fresh biomass contained 10% dry matter (DM) with a crude protein (CP) content of 22% in DM. Other studies with water spinach also indicated that the fresh stems and leaves have CP in range from 20 to 31% in DM, with ash around 31% of DM (Le Thi Men et al 2000; Bui Huy Nhu Phuc 2000; Prak Kea 2003; Chhay Ty and Preston 2005). According to one report (Le Thi Men 2000), chopped water spinach can replace 30% of the DM in feeds for gestating sows and 15% of the diet of lactating sows with improved reproductive performance and welfare.

In many tropical countries, Taro (Colocasia esculenta) is known as a wet-land plant which is cultivated mainly for corm production. In the Southern part of Vietnam, although Taro is commonly grown, farmers normally harvest only the corm, the rest of this plant (leaves and stems) are not used.  In Cambodia, Taro is considered to be a good vegetable crop and is planted near the houses in the late dry season and early rainy season, between April and July. The tubers are used for human consumption while stems and leaves are not widely used for animal feeding. The main reasons for not using them are the itching they cause, and lack of technology. The average tuber yield is 4.5-6 tonnes ha^-1, while the average yield of petiole and leaf is 5-8.5 tones ha^-1 (Pheng Buntha et al 2008).

Some studies report the nutritive value of Taro and that the plants can be used for feeding animals (Pheng Buntha 2006; Chhay Ty 2007; Chittavong Malavanh 2006; Du Thanh Hang and Preston 2008). Calcium oxalate, a substance present as crystals in all parts of this plant, have an effect on the digestive tract by irritating the throat and mouth epithelium (Miller 1929). According to Du Thanh Hang and Preston (2008).  the farmers in Central Vietnam use the taro leaves for pigs by cooking them with rice or rice bran and cassava roots, in order to reduce the concentrate of calcium oxalate. These authors showed that ensiling was equally effective in reducing the calcium oxalate and that there were no differences in crude protein digestibility and N retention between diets with cooked and ensiled taro leaves.

This study was carried out to test the hypothesis that apparent digestibility of DM and CP, and the N retention, would be improved when Taro silage replaced part of the water spinach, as the protein source for growing pigs fed a basal diet of rice bran.

Material and methods

Location and duration

The experiment was conducted in the experimental area of Kampong Cham National School of Agriculture in Kampong Cham province, about 129km from Phnom Penh. Kampong Cham has a tropical climate with an annual monsoon season from May to November. The monsoon is heaviest in late July and August. The climate is most pleasant during the dry season which is from November to April. The annual temperature is around 25^oC with maximum temperature known to reach 32^oC; minimum temperatures rarely fall below 10°C.

The experiment was carried out from 4^th August to 16^th September 2008.

Experimental design

This was as a 3 x 3 Latin Square arrangement (Table 1) with 3 pigs and 3 periods, each of 7 days. The treatments were supplements to the basal diet of rice bran (Photos 1-4) as follows:

• WS: Only water spinach

• TS: Taro leaf and petiole silage

• WS-TS: Mixture of water spinach and Taro silage

Animals and housing

Three crossbred castrated male pigs, with initial live weights of 10.0 ± 2.5 kg, were kept in metabolism cages (0.66cm x 0.63cm x 0.60cm) made of wood and designed to collect faeces and urine separately.

Feeds and feeding

Taro leaves and stems (Photo 1) were harvested from ponds, dried for 24 hours then chopped and ensiled with no additive (Photo 2) as there are soluble sugars in the  petioles of the taro. This procedure has been shown to reduce the content of calcium oxalate (Pheng Buntha 2007). The ensiled taro was stored in plastic bags for 30 days before being used. Water spinach was bought from the farmers and chopped into small pieces (3-5cm). Rice bran was purchased from Kampong Cham market.

The feed components (Table 2) were offered separately with the overall level equivalent to 4% of the live weight (DM basis). The quantities of feeds offered were slightly adjusted to minimize residues. Water was supplied through nipple drinkers.

Measurements and data collection

Feeds offered and residues, faeces and urine were recorded daily during the last 5 days of each period. Urine was collected in a plastic bucket to which sulphuric acid was added to maintain the pH below 4.0 (10ml of a solution of 10% concentrated sulphuric acid). The volume of urine was measured every day and 10% of the total volume stored until the end of each period, when it was analyzed for nitrogen (N). The pigs were weighed in the morning before feeding at the beginning and the end of each period. Feed samples, residues and faeces were analyzed for DM and CP after every period.

Chemical analysis

Feed and faecal samples were dried by microwave radiation to measure the DM content (Undersander et al 1993). Total nitrogen (N) and the organic matter (OM) of samples (feed, faeces and urine) were analysed according to the AOAC (1990) recommendations.

Statistical analysis

The data were analyzed by the General Linear Model option in the ANOVA software of MINITAB (release 13.31) (Minitab 2003).

The sources of variation in the model were treatments, pigs, periods and error.

Results and discussion

Feed composition and intake 

The contents of crude protein were similar for the ensiled taro and the water spinach (Table 3).  The very low level of crude protein in the rice probably indicated some adulteration with a low-protein meal such as cassava root meal. 

There were no differences in intakes of rice bran and the total diet (Table 4). The foliages supplied more than 60% of the dietary crude protein (Figure 1) but only about 30% of the DM intake (Figure 2).

The proportion of diet N derived from the foliages was higher when water spinach was included in the diets;  however, total N intake did not differ among diets (Table 5).

Apparent digestibility coefficients

There were no differences in apparent digestibility of DM, OM and crude protein among the diets (Table 6). 

Nitrogen utilization

Daily N retention and N retention as a percentage of the N intake and N digested did not differ among the diets (Table 7; Figures 7 and 8).  However, when only the diets containing water spinach  (diets WS and WS-TS only) were considered, there were significant relationships between  N retention and N retention as % of digested N and daily intake of water spinach (Figures 9 and 11). By contrast, there were no relationships between taro silage intake and the retention of N for diets WS-TS and TS (Figures 10 and 12). The implication from these contrasting results is that the biological value of the water spinach protein is higher than that of the protein in the ensiled taro leaves and stems.

Figure 9  Relationship between intake of water spinach (diets WS-TS  and WS only) and N retained in pigs fed supplements of water spinach and taro silage with a basal diet of rice bran	Figure 10.  Relationship between intake of taro silage (diets WS-TS  and TS only) and N retained in pigs fed supplements of water spinach and taro silage with a basal diet of rice bran

Figure 11.  Relationship between intake of water spinach (diets WS-TS  and WS only) and N retained  as % of N digested in pigs fed supplements of water spinach and taro silage with a basal diet of rice bran	Figure 12.  Relationship between intake of taro silage (diets WS-TS  and TS only) and N retained as % of N digested in pigs fed supplements of water spinach and taro silage with a basal diet of rice bran

Diuretic effect of water spinach

It was observed that the urine volume was greater on the diets that contained water spinach (Figures 13 and 14) and also the colour was different (Photo 3). The different volume and colors of urine observed in this research may  be explained by the diuretic effect of water spinach. Chittavong Malavanh and Preston (2006) reported that urine volume in pigs increased when water spinach replaced sweet potato leaves in  a basal diet of rice bran and cassava root meal. A similar result was observed in an experiment by Phiny et al (2008), in which urine volume increased when water spinach replaced mulberry leaves in pig diets. In the experiments of Chittavong Malavanh and Preston (2006) and Phiny et al (2008), the increased urine volumes were associated with increased excretion of N; however, this was not the case in the present experiment (Table 7). It appears that water spinach may have a negative on nitrogen utilization when it exceeds 25 to 30% in the diet DM. Thus, when it was fed at 50% of the diet (Chhay  Ty et al 2005) the increased urine volumes were combined with increased excretion of N and lower retention of N as % of digested N.

Conclusions

 - Coefficients of apparent digestibility of DM and crude protein  and all measures of N utilization were high on all the diets.

 - Thee were indications that replacing the taro silage with water spinach led to increases in:

• Daily N retention

• N retention as % of N digested

• Urine volume 

Acknowledgements

The author would like to thank the MEKARN program, financed by Sida/SAREC for supporting this mini-project.

We are very grateful to doctor Do Van Xe, Mr Chhay Ty and Ms Latsamy for all their great help and support during the experiment. Thanks are given to the staff, students of Kampong Cham National School of Agriculture and classmates of Mekarn course 2008-2010 for helping to carry out this research.

References

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