Effect of Taro (Colocasia esculenta) leaf + stem silage and mulberry leaf silage on digestibility and N retention of growing pigs fed a basal diet of rice bran

Ty Chhay, Khieu Borin and T R Preston

Center for Livestock and Agriculture Development,
Pras Teat village, Rolous commune, Kandal Stung district, Kandal province.
PO Box 2423 Phnom Penh 3, Cambodia
chhayty@celagrid.org

Abstract

Three crossbred castrated male pigs, weighing on average 24 kg were allotted at random to 3 diets within a 3*3 Latin square, to study the effect of Taro (Colocasia esculenta) silage (leaves + stems) and mulberry leaf silage, or a 50:50 combination of both foliages, on digestibility and N retention of growing pigs fed a basal diet of rice bran. The rice bran was restricted at 1% of body weight (DM basis) while the silages were fed ad libitum.

Diets with 67% of mulberry leaf silage plus 33% rice bran and 74% Taro (leaf + stem) silage with 26% rice bran (DM basis) supported relatively high rates of feed intake (30 and 39 g DM/kg LW/day). The mixed silage (50:50 as DM of each forage) was consumed at 36 g/kg LW/day. Apparent digestibility coefficients for DM, crude protein, NDF and ADF were higher for diets containing Taro silage compared with mulberry silage alone, with no difference between 50% Mulberry-50% Taro silage and 100% Taro silage. N retention when corrected for N intake did not differ among diets.

It is concluded that the protein in Taro foliage (leaves + stems) is more digestible than the protein in mulberry leaves but that the biological value of the protein is similar for both foliages.

Key words: Biological value, feed intake, leaves, protein.

Introduction

It  has been argued recently that the challenges posed by global warming and resource depletion (Leng 2009) can best be met by developing feeding systems that make better use of locally available feed resources (Preston 2009). In tropical countries such as Cambodia, where rice is the staple food, the most widely available feed for pigs is rice bran. This feed is low in protein which is traditionally provided by supplementing it with soya and/or fish meals, the prices of which have increased steadily in recent years. This has been the reason for examining alternative protein sources that are readily available as byproducts of food crops (eg: leaves of cassava Manihot esculenta and vines of sweet potato Ipomoea batatas) or which grow naturally in forests and ponds (eg: water spinach Ipomoea aquatica and Taro species (Colocasia esculenta, Alocacia macrorrhiza and Xanthosoma sagittifolium). Results of recent research with these protein-rich plants were reported in a workshop held in Cambodia in 2006 (http://www.mekarn.org/proprf.content.htm).

It is well understood that the major constraint to the efficient use of protein-rich foliages is the barrier to the digestibility of the protein posed by the presence of the lignified cell wall components that provide the supporting structures in most plants  (Jørgensen et al 1996; Kass et al 1980, Ogle 2006). Recently, it has been observed that Taro (Colocacia esculenta) differs from most plants in that the concentration of the major cell wall fractions (Neutral detergent fibre - NDF and acid detergent fibre - ADF) is lower in the stems than in the leaves while the soluble components of the cell – as soluble sugars - are higher in the stems (Dao Thi My Tien et al 2010). It has also been observed that foliages of New Cocoyam and Taro can be ensiled easily without the need for additives, provided the stems – which are rich in sugars - are included as well as the leaves (Rodíguez et al 2009; Dao Thi My Tien et al 2010). Because of these nutritional advantages the foliage of the Colocacia species appears to be one of the most promising candidates for supplementing the rice bran as the basal diet of pigs.

The aim of the experiment reported in this paper was to determine coefficients of digestibility and N retention in growing pigs fed silage made from Taro foliage (leaves + stems) or from the leaves of mulberry (Morus alba) as the only supplements to a basal diet of rice bran.

Materials and Methods

Location

The experiment was carried out at the Center for Livestock and Agriculture Development (CelAgrid), located in Preah Theat village, Rolous commune, Kandal Stung district, Kandal province, approximately 25 km from Phnom Penh city. The experiment began on November 18^th and finished on December 20^th 2009.

Treatments and design

The three treatments within a 3*3 Latin square arrangement (Table 1) were:

·         ML: Mulberry leaf silage

·         TF: Taro foliage silage

·         ML-TF: Silage of mixed mulbery leaves and Taro foliage (50:50 DM basis)

Animals and housing

Three castrated male pigs (Landrace*Large White) weighing on average 24kg were housed in metabolism cages during the whole trial (36 days). The metabolism cages (80cm*80cm) were built to allow the quantitative collection of faeces and urine. The characteristics of the cages have been described elsewhere (Chhay Ty et al 2003a,b). Each experimental period consisted of 12 days; 7 days for adaptation to the diets followed by another 5 days for collection of samples of feed offered, feed residues, feces and urine.

Photo 1.  The metabolism cage allowing free movement of the animals

Experimental feeds and feeding

Taro foliage was harvested from lakes and ponds (Photo 2) in the vicinity of the CelAgrid farm. The mulberry leaves were harvested from plants growing in the farm (Photo 3). The Taro foliage (leaves and stems) were chopped by machine and then ensiled without adding any other ingredient and stored for one month before feeding to the pigs. The mulberry leaves were ensiled with sugar palm syrup (5% fresh basis) and stored for the same one month period. For the mixed silage no additive was used. Rice bran was purchased from the local rice mill.

Photo 2: Taro growing wild in ponds close to CelAgrid	Photo 3: Mulberry leaves from the CelAgrid farm

 The silages were offered to appetite, adjusting offer levels to minimize refusals. Rice bran was restricted at 1% of body weight (DM basis). The pigs were fed thrice daily with equal rations at 8:00 am, 12:00 am and 4:00 pm. Rice bran was fed first to make sure there was no residue of the energy component; silages of Taro and mulberry were fed later. Drinking water was permanently supplied through drinking nipples. The animals were weighed at the beginning and end of each experimental period.

Data collection

Samples of feeds offered, refusals, urine and feces were collected every day and 10% of the amount stored at -18 C until the end of each collection period of 5 days. A representative sample was obtained from every treatment, mixed thoroughly by hand and then homogenized in a coffee grinder for analysis of DM, N, ADF and NDF. Urine was collected in a plastic bucket to which sulphuric acid was added to maintain the pH below 4.0 (10ml of concentrated H₂SO₄). The volume of urine was measured every day and 10% of the volume stored at -18 C until the end of each period, when a sample was taken for analysis of N.

Chemical analyses

Chemical analyses of the feed ingredients and feces were undertaken following the methods of AOAC (1990) for ash and N. ADF and NDF were determined following the methods of Goering and Van Soest (1970) and Van Soest et al (1991). The DM content was determined using the microwave method of Undersander et al (1993). The N content of urine was determined by AOAC (1990) procedures. 

Statistical analyses

The data were subjected to analysis of variance according to the general linear model of the Minitab software (Minitab release 13.31, 2000). Sources of variation were: pigs, period, treatment and error. The Tukey test in the Minitab software was used to identify differences amoing mens values.

Results and discussion

Chemical composition of feeds

Values of NDF and ADF were lowest in mulberry silage and highest in rice bran (Table 2). The mulberry leaf silage was higher than the Taro silage in crude protein.

Feed intake

The recorded intakes of the feeds (Table 3) showed that the crude protein content decreased according to the proportion of Taro silage consumed. The silages represented from 67 (mulberry) to 74% (taro) of the total DM intake. The daily DM intake, and the proportion in the form of forage, increased with increasing proportion of Taro silage in the diet (Table 4).

Apparent digestibility

Apparent digestibility coefficients were higher for the diets containing Taro silage compared with mulberry silage alone, with no difference between 50% Mulberry-50% Taro silage and 100% Taro silage as the protein supplement (Table 5; Figures 3 to 6). The data for NDF and ADF digestibility indicate that the cell wall components in the Taro foliage are less lignified than those in mulberry leaves. Inclusion of the stem as well as the leaves in the Taro silage may have been a factor here as it has been shown that the stem contains less NDF and ADF than the leaves (Dao Dao Thi My Tien et al 2010). 

Figure 3: DM digestibility in pigs fed Taro foliage silage or and mulberry leaf silage, or mixtures of the two, with basal diet of rice bran	Figure 4: Crude protein digestibility in pigs fed Taro foliage silage or mulberry leaf silage, or mixtures of the two, with basal diet of rice bran
Figure 5: ADF digestibility in pigs fed Taro foliage silage or mulberry leaf silage, or mixtures of the two, with basal diet of rice bran	Figure 6: NDF digestibility in pigs fed Taro foliage silage or mulberry leaf silage, or mixtures of the two, with basal diet of rice bran

N balance

N intake and N retention increased on the diets with mixed Taro and mulberry silage or Taro silage alone, compared with mulberry silage alone (Table 6; Figure 7). There were no differences among treatments when the N retention data (Figure 8), and N retention as a percentage of N digested, were corrected for differences in N intake.

Figure 7. N retention by pigs fed Taro foliage silage or mulberry leaf silage, or mixtures of the two, with basal diet of rice bran	Figure 8. N retention by pigs fed Taro foliage silage or mulberry leaf silage, or mixtures of the two, with basal diet of rice bran. (#data corrected for differences in N intake)

The use of protein-rich foliages in pig diets as complete replacements for conventional protein supplements such as fish meal and soybean meals is a relatively recent development (Ogle 2006; Preston 2006). Much of the research has been directed to the use of single foliages such as those from cassava (Chhay Ty et al 2007c, 2009), sweet potato (Le Van An et al 2004, Chhay Ty et al 2007), water spinach (Chhay Ty et al 2005a,b, 2006, 2007b), mulberry leaves (Chiv Phiny et al 2003), Taro (Chhay Ty et al 2007d, Chhay Ty et al 2009b, Buntha et al 2008a,b, ChittavongMalavan et al 2008, Du Thanh Hang and  Preston 2008). Chhay Ty et al (2005b) evaluated the use of cassava leaves and water spinach alone, or as 50:50 mixtures (DM basis), as sole supplements to a basal diet of broken rice. They reported a synergistic effect from the inclusion of water spinach, as pig performance on the mixture of the two foliages was superior to the average of the foliages fed as the sole supplement. There was an indication of a similar synergistic effect between mulberry and Taro silages in the present study, as there were no differences in intake and apparent digestibility coefficients, between Taro silage as the only supplement and the 50:50 combination of Taro and mulberry silages, while both were superior to mulberry silage alone.

The fact that there were no differences among the treatments, for N retention corrected for N intake and N retention as a percentage of N digested, indicates that were no differences in the biological value of the proteins in Mulberry and Taro foliage. As was postulated in the introduction, the differences in nutritive value among foliages as protein supplements in pig diets is primarily due to differences in digestibility and not in the balance of amino acids.

Conclusions

• Diets with 67% of mulberry leaf silage plus 33% rice bran and 74% Taro (leaf + stem) silage with 26% rice bran (DM basis) supported relatively high rates of feed intake (30 and 39 g DM/kg LW/day) in growing pigs (25g LW).  A mixed silage (50:50 as DM of each forage) was consumed at 36 g/kg LW/day.
  
  
• Apparent digestibility coefficients for DM, crude protein, NDF and ADF were higher for diets containing Taro silage compared with mulberry silage alone, with no difference between 50% Mulberry-50% Taro silage and 100% Taro silage.
  
  
• N retention when corrected for N intake did not differ among diets.
  
  
• It is concluded that the protein in Taro foliage (leaves + stems) is more digestible than the protein in mulberry leaves but that the biological value of the protein is similar for both foliages.

Acknowledgments

The authors would like to express their gratitude to the MEKARN project financed by Sida and to the Center for Livestock and Agriculture Development (CelAgrid), for providing resources for conducting this experiment.

References

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Received 6 February 2010; Accepted 10 May 2010; Published 10 June 2010

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