Effect of Taro (Colocasia esculenta) leaf silage as replacement for fish meal on feed intake and growth performance of crossbred pigs
 

Pheng Buntha, Khieu Borin, T R Preston* and B Ogle**

Center for Livestock and Agriculture Development
buntha@celagrid.org
*Finca Ecológica, TOSOLY, Socorro Colombia
**SwedishUniversity of Agricultural Sciences, Department of Animal Nutrition & Management,
 PO Box7024, 75007,Uppsala, Sweden

Abstract

Eighteen crossbred (Large White x Local) male pigs with initial body weight of 20.9± 0.29 kg were allocated randomly into 3 treatments replicated 6 times, with one pig in each pen. The treatments were ensiled leaves of taro (Colocasia esculenta) replacing 0 (FM), 50 (FM-TS) or 100 (TS) % of the protein from fish meal in a basal diet of sugar palm syrup and rice bran.

Total dry matter feed intake was lower in TS than in FM and FM-TS (P<0.01), also when expressed on a live weight basis (37.8, 41.9 and 33.1 g/kg for FM, FM-TS and TS, respectively) (P<0.01). Average daily gain was highest for FM-TS (278g), followed by FM (226g) and TS (119g) (P<0.05). Dry matter feed conversion and cost of feed per kg gain were highest for TS (8.79 kg/kg gain and 2.24 US$/ kg gain, respectively) and lowest for FM-TS (4.69 kg/kg gain and 1.09 US$/kg gain, respectively) (P>0.05). Daily gains and feed conversion were only around 50% of the genetic potential of the pigs for these traits. Further research is needed to identify the true constraints to pig growth when protein from ensiled taro leaves is a major component of the diet.

Key words: Feed conversion ratio, growth, silage, sugar palm syrup,
 

Introduction

It is common practice for farmers in rural areas of Cambodia to keep a few local or crossbred pigs in a scavenging system with supplementation of locally available resources, such as rice bran, broken rice, kitchen waste, banana stems, water spinach and other water plants. The live weight gain is low, probably because of the poor quality of the feed, parasite infection and other diseases. In contrast, in the commercial farms the diets are usually based on soybean, cereals and fishmeal. However, this strategy is not appropriate for smallholder farmers because of the high costs of conventional feed ingredients. The proteins in the leaves of many soil and water plant, being composed mostly of enzymes necessary for the growth of plant tissue, have an amino acid balance that resembles the "ideal" protein (Preston 2006). They should therefore be suitable to replace the fish meal and soybean meal used in commercial balanced feeds.

According to Ogle (2006), the constraints in many leaves are the anti-nutritional factors, such as cyanogenic glycosides, trypsin inhibitors, mimosine, goitrogens, oxalic acid, tannins and saponins. Linkages between the protein and fibre can result in decreased digestibility (Jørgensen et al 1996; Kass et al 1980; Shayo and Uden 1999). From studies on the nutritive value of tropical leaves for pigs, Leterme et al (2005) concluded that tropical tree leaves offer a variable amount of proteins that are well balanced in essential amino acids but not well digested by pigs.

Taro is a tropical food crop with high potential because of the high yield of the roots (or corms) and foliage. The leaves are rich in protein and easy to ensile, which has been shown to reduce markedly the concentrations of calcium oxalate (Pheng Bunta et al 2007), which appears to be a limiting factor in consumption of the fresh leaves according to Tiep et al (2006). In the research by Pheng Bunta et al (2007), it was shown that taro leaf silage could replace up to 70-75% of the fish meal protein, with higher feed intakes and N retention than with 100% of the protein from fish meal or from taro leaf silage.

The present study was designed to evaluate taro leaf silage in a pig growth trial in order to make an economic assessment of its value relative to fish meal as the main protein source in the diet. In this trial rice bran was included at 20% of the diet, because it was observed that the pigs were reluctant to consume a diet composed only of syrup from sugar palm (Borassus flabellifer) and fish meal, perhaps because of the absence of fibre in the diet and a possible deficiency of essential long chain fatty acids.
 

Materials and methods

Location and Climate

The study was carried out from December 2006 to March 2007, at the Centre for Livestock and Agriculture Development (CelAgrid) located in Kandal village, Rolous commune, Kandal Stung district, Kandal Province, Cambodia. The climate is tropical monsoonal, with two seasons: a dry season (November-April) and a rainy season (May-October).

Experimental design

Eighteen (Large White x Local) crossbred male pigs with initial body weight of 20.9± 0.29 kg were allocated randomly into 3 treatments, replicated 6 times, with one pig in each pen. The sources of energy were sugar palm syrup and rice bran. The pigs were assigned to treatments in a randomized complete block design (RCBD), with the blocks being the initial live weight (Table 1).

Table 1. Experimental layout for the growth performance trial
Block I mean LW 25 kg	Block II mean LW 23 kg	Block III mean LW 22 kg	Block IV mean LW 20 kg	Block V mean LW 18 kg	Block VI mean LW 18 kg
FM	TS	FM-TS	TS	TS	FM-TS
TS	FM-TS	FM	FM	FM-TS	FM
FM-TS	FM	TS	FM-TS	FM	TS

The experimental treatments were:

FM : Fish meal + palm syrup + rice bran

FM-TS : Taro leaf silage + fish meal + palm syrup + rice bran

TS : Taro leaf silage + palm syrup + rice bran

The protein levels in diets FM-TS and TS were increased relative to diet FM to adjust for the observed lower digestibility of the taro leaf protein (Pheng Buntha et al 2007).

Diets and feeding

The collection and ensiling of the taro leaves and the sources of the palm syrup and fish meal were the same as described by Pheng Buntha et al (2007).  Rice bran was purchased from a local rice mill. The pigs were fed ad libitum 3 times per day. All ingredients were mixed together before feeding (see Table 2). Fresh water was available at all times from nipple drinkers. The duration of the experiment was 3 months.

Measurements and data collection

Feed offered and feed residues were recorded daily. The animals were weighed in the morning before feeding at the beginning and the end of the experiment and at 10 day intervals. Samples of feed offered and residues were analysed for DM and N every 10 days.

The measurements taken were as below:

• Growth rate (g/head/day)

• Daily feed intake (kg/head/day)

• Feed conversion ratio (kg feed/kg weight gain)

• Feed cost (USD/kg weight gain)

Chemical analysis

Feed ingredients were analyzed for DM by microwave radiation (Undersander et al 1993). Total N contents of feeds and residues were determined by the Kjeldahl procedure as outlined by AOAC (1990).

Statistical analysis

The data (feed intake, weight gain and feed conversion) were analyzed according to the analysis of variance technique using the general linear model (GLM) procedure in the software of MINITAB (release 13.31). The sources of variation were treatments, blocks and error.
 

Results and discussion

Feed intake

The highest DM intake was recorded for treatment FM-TS (Table 3) and lowest for TS. The reason why the TS pigs were unable to consume the same amount of DM as those on FM-TS may have been the more voluminous nature (bulkiness) of this diet, while on treatment FM it appeared that the problem was the poor acceptability of the mixed ingredients. According to Kyriazakis and Emmans (1995) and Whittemore et al (2002), feed intake in pigs offered high-bulk feeds is restricted due to physiological constraints for the animal. Bulkiness is said to be due to the swelling of hydrated fibre and the final volume depends on fibre composition and structure (Bach Knudsen 2001). Leterme et al (2005) showed that intakes of Xanthosoma leaves by sows were twice as high when these were fed dry compared with the fresh state, but that the water-holding capacity (WHC) was the same for both. They considered that WHC alone could not explain the effects of bulkiness. Chhay Ty et al (2007) reported similar findings to Leterme et al (2005) in that pigs fed ground sun-dried leaves of taro (Colocasia esculenta) consumed more DM than when fed ensiled leaves. More research is needed in order to elucidate the factors determining the intake of taro leaves.

The actual amounts of protein as a percentage of DM that were consumed corresponded approximately to the planned proportions of crude protein in the diet DM, therefore the concentration of dietary protein in the different diets would not appear to have been a factor influencing feed intake.

Live weight gain and feed conversion

The average growth curves for the different treatments (Figure 1) indicate a long period of adaptation on the 100% taro leaf silage diet (TS). There was a shorter period of adaptation on the 50:50 fish meal: taro leaf silage diet (FM-TS) and a suggestion that towards the end of the trial period the pigs on this treatment were growing considerably faster than on the other two treatments.

The analysis of the data for final live weight and daily live weight gain paralleled that for DM intake, with the best performance on the FM-TS diet (Table 3; Figure 2). DM feed conversion appeared (P=0.11) to be worse on the TS diet (Table 3; Figure 3).

The growth rates even on the best diet (FM-TS) (278 g/day) were much less than was reported by Rodriguez et al (2006) (524 g/day) for pigs over the same live weight range and fed diets based on sugar cane juice with equal quantities of the protein provided by soybean meal and fresh leaves of New Cocoyam (Xanthosoma sagittifolium). The growth rate on this diet was similar to what was recorded in pigs fed a diet where all the protein was provided by soybean meal (519 g/day). The difference in growth rate on fresh Xanthosoma leaves (Rodriguez et al., 2006a) as protein source and on ensiled Colocasia leaves in the present study was mirrored in the differences in N retention (9.7 and 7.5 g/day for 30 and 60% replacement of soybean meal by Xanthosoma leaves in Rodriguez et al (2006b); and 4.58 g/day for diets with 50% of the protein from ensiled taro leaves (Pheng Buntha et al 2007). There is no apparent explanation for these differences, unless the leaves of taro (Colocasia esculenta) contain as yet unidentified anti-nutritional factors or that the ensiling process results in loss of protein quality (ie; by fermentation of part of the protein to non-protein-nitrogen (Oshima and McDonald 1978)).

Feed costs were lowest for the FM-TS diet, indicating that a mixture of fish meal and taro leaf silage can be the most economical for small-holder farmers.

Conclusions

• The growth performance of pigs fed sugar palm syrup and rice bran was better when fish meal and ensiled taro leaves provided equal proportions of supplementary protein than when fish meal or ensiled taro leaves were the only supplements.

• However, on the best treatment the growth rate and feed conversion were only some 50% of the genetic potential of the pigs for these traits.

• Further research is needed to identify the true constraints to pig growth when protein from ensiled taro leaves is a major component of the diet.
   

Acknowledgments

The present experiment is part of a study on ensiled taro (Colocasia esculenta) leaves in diet of local crossbred pigs in Cambodia, supported by the MEKARN project financed by Sida-SAREC. The authors express their gratitude to all the personal of the CelAgrid Ecological Farm, for help with the experiment. This paper forms part of the MSc thesis (MEKARN-SLU, Uppsala, May 2007), of the senior author.
 

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