Replacing taro (Colocasia esculenta) silage with protein-enriched cassava root improved the nutritive value of a banana stem (Musa spp) based diet and supported better growth in local pigs (Moo Laat breed)

Nouphone Manivanh and T R Preston¹

Faculty of Agriculture and Forest Resource, Souphanouvong University, Luang Prabang, Lao PDR
noumanivanh@gmail.com
¹ Centro para la Investigación en Sistemas Sostenibles de Producción Agropecuaria (CIPAV),
Carrera 25 No 6-62 Cali, Colombia

Abstract

A growth trial was conducted with 12 local pigs (Moo Lat breed) with average 14.8 kg initial live weight in a randomized complete block design (RCBD), with three replications of four treatments. The aim of the study was to determine the effect of replacing ensiled taro foliage with protein-enriched cassava root in a basal diet of ensiled banana stem.

Fermentation of fresh cassava root with yeast, urea and di-ammonium phosphate (DAP) increased the content of true protein in the root from 2.5 to 14.2% in DM. There were positive responses in dry matter (DM) intake, live weight gain, feed conversion ratio, apparent DM digestibility and N retention as the percentage of protein-enriched cassava root in the diet was increased.

Key words: DAP, digestibility, feed conversion, indigenous pigs, live weight gain, N retention, yeast

Introduction

Smallholder agricultural systems in Lao PDR are mixed farming systems including staple and cash crops as well as livestock production. In this context, pig production plays an important role as a source of income and capital accumulation for use at critical times (rice shortage, medical treatment or marriage). In 2008, there were about 2,460,000 pigs in Lao PDR (DLF 2008), and approximately 85% of these were kept in smallholder systems (Conlan et al 2008), mainly in the mountainous regions (Thorne 2005; Phengsavanh and Stür 2006).

Most pigs in rural areas of Lao PDR are raised in traditional, low input, free and semi-free scavenging systems, where the pigs are allowed to scavenge freely for feed all the year round or after the main crops have been harvested (Phengsavanh et al 2010). The main feed resources are agricultural by-products and vegetables and weeds that grow in forests, along the banks of streams and in cropping areas. These feed resources are vulnerable to seasonal weather changes and in the dry season feed is always in short supply. Thus, one of the main limitations to pig production in these smallholder production systems is a shortage of feed. Apart from this feed shortage, infectious diseases are also a problem that limit productivity (Conlan et al 2008; Phengsavanh and Stur 2006; Thorne 2005).

Taro (Colocasia esculenta) is a food crop which provides high yield of roots (or corms) and foliage. Leaves from Taro are rich in protein, vitamins and minerals. However, they also contain oxalic acid salts which cause itching of the mucosal surfaces in the mouth and throat which reduces feed intake (Du Thanh Hang and Preston 2008). Farmers traditionally boil the leaves and petioles to overcome this problem, but this can be expensive requiring wood or other sources of fuel. Recently, ensiling the Taro foliage has been developed and has proved to be effective in reducing the oxalate content (Hang et al 2011). Initially molasses was used in the ensiling process (Malavanh et al 2008); however, the finding that the petioles contained a considerable level of soluble sugars led to the idea of ensiling the leaves and petioles together (Rodríguez and Preston 2009), obviating the need for additional molasses.

Farmers in Lao PDR often use fresh banana stem as feed for pigs by mixing it with rice bran. Banana stem is low in nutrients especially protein (CP 5.1% in DM) and is high in fiber (CF 29% in DM) (http://www.feedipedia.org). The nutrient status was improved when taro foliage was mixed with the banana stem and the mixture was ensiled (Dao Thi My Tien et al 2010; Manivanh and Preston 2015; Sivilai et al 2016).

In Lao PDR as in most tropical countries the most widely grown crops are primarily sources of carbohydrate (eg: rice, sugar cane, cassava). Few crops are grown specifically as sources of protein. As a result, protein rich feeds such as soybean meal are imported in order to produce balanced diets for livestock especially pigs and poultry. An alternative approach that has been studied by several researchers is the solid state fermentation of carbohydrate-rich byproducts from these crops using combinations of fungi and yeast (Phiny et al 2012; Phong et al 2013; Khempaka et al 2011; Hong and Ca 2015) in order to enrich the content of protein.

The aim of the research reported in this paper was to apply the protein-enrichment technique to raise the protein content of cassava roots and to evaluate the use of this product as partial replacement of Taro silage in a banana stem- based diet fed to Moo Laat pigs

Materials and methods

Location and climate of the study area

The experiment was carried out from September 2015 to December 2015 at the Faculty of Agriculture and Forest Resource in Souphanouvong University. The site is located 7km from Luang Prabang City, Lao PDR. The mean daily temperature in this area at the time of the experiment was 27 ^oC (range 22-32 ^oC).

Experimental design, treatments and management

Protein-enrichment of cassava root

Cassava roots (60 kg) were peeled and chopped by hand into small pieces (1-2 cm), and steamed for 30 minutes. For the steaming a 200 liter steel barrel was used. This had a false floor of bamboo strips supported by wooden boards 30cm above the base of the barrel. The space beneath the bamboo strips contained water which was maintained at boiling point by a wood fire underneath the barrel (Photos 1; 2 and 3).

The steamed cassava root was removed from the barrel and cooled for 15 minutes then mixed with urea, di-ammonium phosphate (DAP) and yeast in proportions of 3, 0.8 and 2%, respectively, of the cassava DM (Photo 4). According to www.feedipedia.org: Diammonium phosphate contains 21.4% N and 23.7% P; Urea has 46%N (DM basis); yeast contains 48.6% CP in DM.

The mixed substrate was then transferred to bamboo baskets covered with plastic netting to allow free entrance of air (Photo 5). On each of 3 consecutive days the contents of the basket were turned so that all the contents were exposed to the air entering through the top and the sides of the basket. After three days, the protein-enriched cassava root (Photo 6) was fed to the pigs.

Photo 1. Wooden boards 30cm above the base of the barrel	Photo 2. The bamboo strips placed above the boards
Photo 3. The steaming of the cassava root	Photo 4. Mixing cassava root with urea, diammonium phosphate (DAP) and yeast
Photo 5. The mixed substrate was put in bamboo baskets covered with plastic netting	Photo 6. The protein-enriched cassava root

Ensiling Taro foliage and banana stems

Taro (Colocasia esculenta) leaves and petioles were collected from areas around the University and were chopped into small pieces (2-3 cm length). They were wilted for 24h to reduce the moisture content and ensiled, without additive, in 50 liter polyethylene bags for 14 days (Photos 7, 8, 9 and 10). Banana stems were bought from a nearby village. They were chopped by hand into small pieces and ensiled in 200 liter PVC containers for 14 days (Photos 11-12).

Photo 7. Taro (Colocasia esculenta) were chopped by hand	Photo 8. Taro (Colocasia esculenta) were wilted for 24h to reduce the moisture
Photo 9. Taro silage in the plastic bag	Photo 10. Ensiled taro after 14 days
Photo 11. Banana stems were chopped by hand into small pieces	Photo 12. Ensiled banana stems in 200 liter PVC

Experimental design

The experiment was arranged in a completely randomized block design (CRBD) with 4 treatments and 3 replications.

Individual treatments were different proportions (DM basis) of protein-enriched cassava root (PECR) replacing taro silage (TS) with constant proportions of ensiled banana stem (EBS):

• PECR0: Taro silage (TS) 60% + ensiled banana stem (EBS) 40%

• PECR5: TS 55% + EBS 40% + Protein-enriched cassava root (PECR) 5%

• PECR10: TS 50% + EBS 40% + PECR 10%

• PECR15: TS 45% + EBS 40% + PECR 15%

Twelve local pigs (Moo Lat breed) with a mean body weight of 14.8 kg (8 males; 4 females) were bought from a pig farm in Luang Prabang Province. They were vaccinated against swine fever and treated against round worms with Ivermectin (1ml/20kg LW), before starting the experiment. The pigs were housed in individual pens (width 1m and length 1.2m) made from local materials (Photos 13 and 14). The pigs had free access to water and were adapted to the pens and the feeds for one week before starting the experiment which lasted 90 days.

The diet ingredients were mixed together and given two times per day at 6:30 am and 5:00 pm, the amount being based on an offer level of 40g DM/kg live weight.

Photo 13. Housing made from local materials	Photo 14. Moo Lat pig used in the experiment

Data collection

The pigs were weighed in the morning before feeding, at the beginning of the trial and every 15 days. Live weight gain was determined from the linear regression of live weight on days in the experiment. Samples of feed offered and refused were collected daily, weighed and sub-samples stored in the refrigerator at 4°C before being bulked for analysis of DM, N and ash.

Feces and urine were collected over 5 day periods at intervals of 15 days throughout the experiment. Each day 20 ml of 15 % H₂SO₄ were added to the urine container to maintain the pH of the urine below 4.0. All the feces were stored in the refrigerator until the end of the collection period when they were mixed and a sub-sample taken for analysis of DM, ash and N. A sub-sample of urine was taken daily and stored in the refrigerator until the end of the collection period when the samples were mixed and a sub-sample taken for analysis for N.

Chemical analysis

AOAC (1990) methods were used to analyse the sub-samples of feeds offered and refused and of feces for DM, N and ash and of urine for nitrogen. True protein in the enriched cassava root was determined by prior treatment of the samples with Trichlor-acetic acid (TCA) before estimation of N.

Statistical analysis

Data for feed intake, N intake, N retention, live weight were analysed with the General Linear Model option of the ANOVA program in the MINITAB software (Minitab 2000). Sources of variation were treatments and error.

Results

Chemical composition

After adding the urea, DAP and yeast to the cassava root, prior to the start of the fermentation, the CP in the mixture was calculated to be 13% in DM (Table 1) of which 4.3% was estimated to be in the form of true protein (from the cassava root and the yeast).

After fermentation, the crude and true protein values were 16.7 and 14.2% (in DM). The increase in crude protein concentration after fermentation, relative to the level at the beginning, was assumed to be due to loss of substrate DM (of about 23%) providing energy for growth of the yeast.

Feed intake, growth rate and feed conversion

DM intake was increased linearly with the increase in the level of protein-enriched cassava root (Table 3; Figures 1 and 2).

Figure 1. Effect of supplementation with PECR on DM intake of pigs by replacing taro silage and ensiled banana stem as a basal diet

The live weight gain of the pigs (Table 4) was increased by 46% with a linear trend (Figure 2) as the protein-enriched cassava root was increased from zero to 15% of the diet. The DM feed conversion followed a similar trend with a curvilinear improvement as the proportion of protein-enriched cassava root in the diet was increased (Figure 3).

Figure 2. Relationship between live weight gain and PECR content of the diet

Figure 3. Relationship between feed conversion ratio and PECR content of the diet

Apparent digestibility and N retention

The coefficients of apparent digestibility of OM and CP were increased with increasing levels of protein-enriched cassava root in the diet (Table 5). Daily N retention and N retention as a percentage of the N intake and N digested were all improved by supplementation with protein-enriched cassava root (Table 4; Figures 4 and 5).

Figure 4. Relationship between N retention and proportion of PECR in the diet

Discussion

The increase in the true protein content of the cassava root by fermentation with yeast, urea and DAP agrees with the findings of many researchers. Krisada et al (2009) carried out a similar fermentation with fresh cassava root using urea and yeast. The crude protein was increased from 3.2 to 21.1% in DM with 90% of the crude protein in the form of true protein. Fermentation of cassava peels by a pure culture of S. cerevisiae increased the protein content from 2.4% to 14.1% (Antai and Mbongo 1994). Oboh and Kindahunsi (2005) reported that the fermentation of cassava flour (pulp??) with S. cerevisiae increased the protein level from 4.4% to 10.9% in DM.

The increase in growth rate (46%) by replacing Taro silage with protein-enriched cassava root was comparable with that (32%) reported in an earlier experiment (Manivanh and Preston 2015). DM feed conversion in the present experiment (4.7) was also better than in the previous experiment (5.7). The improvement in pig performance by replacing ensiled Taro foliage with protein-enriched cassava root could be a reflection of the higher energy value in the latter (% crude fiber in DM of 3.7 in cassava root compared with 11% in Taro foliage [Hang et al 2015]).

Conclusions

• There were positive linear responses in DM intake, live weight gain, feed conversion, apparent digestibility and N retention when protein-enriched cassava root partially replaced taro silage in a basal diet of ensiled banana stem fed to Moo Lat pigs.

Acknowledgements

This research is part of the requirement by the senior author for the degree of PhD in Nong Lam University, Vietnam. The authors acknowledge financial support for this research from the MEKARN II project financed by Sida. Special thanks are given to the students (Mr. Khamtan Soukthong and Mr. Somephone Kashearher) for their practical help during the experiment.

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Received 10 January 2016; Accepted 23 April 2016; Published 1 May 2016

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