Protein-enriched cassava (Manihot esculenta Crantz) root as replacement for ensiled taro (Colocasia esculenta) foliage as source of protein for growing Moo Lat pigs fed ensiled cassava root as basal diet

Vanhnasin Phoneyaphon and T R Preston¹

Faculty of Agriculture and Forest Resource, Souphanouvong University, Luang Prabang, Lao PDR
Vanhnasin83@gmail.com
¹ Centro para la Investigación en Sistemas Sostenibles de Producción Agropecuaria (CIPAV),
Carrera 25 No 6-62 Cali, Colombia

Abstract

This study was carried out to determine the extent to which protein-enriched cassava root (PECR) could replace ensiled taro foliage as the protein source for recently weaned Moo Lat pigs fed ensiled cassava root as the source of carbohydrate. Sixteen female pigs of local breed (Moo Lat) with average initial live weight of 9.8 kg were allocated to 4 treatments in a completely randomized block design with four replicates. The treatments were levels of PECR at 0, 20, 40 and 60% (DM basis) replacing ensiled Taro foliage in a basal diet of ensiled cassava root.

Anaerobic fermentation of cassava root with urea, DAP and yeast (PECR) increased the crude protein from 3 to 14.5% in DM; true protein was increased from 1.5 to 7.8% in DM. Growth rate of the pigs was increased by 16% from 150 to 175 g/day, when PECR replaced one third of the ensiled Taro foliage. With complete substitution of ensiled taro foliage by PECR the growth rate decreased to 128 g/day. DM feed conversion was best (3.47) with 27% of the dietary protein from PECR and poorest (4.21) when PECR was the only protein supplement.

Key words: carbohydrate, feed conversion, growth performance, live weight, protein

Introduction

Cassava root is rich in digestible carbohydrate but with a very low content of protein. One way to improve the protein content of carbohydrate-rich feeds is by solid-state fermentation with yeast and fungi (Araujo et al 2008; Hong and Ca 2013). Fermentation of cassava peels by a pure culture of S. cerevisiae increased the protein content from 2.4% to 14.1% according to Antai and Mbongo (1994) while the fermentation of cassava root meal with S. cerevisiae enhanced the protein level from 4.4% to 10.9% in DM and decreased the cyanide content according to Oboh and Kindahunsi (2005). Fermentation has been found to be an efficient method for reducing the concentration of HCN in cassava leaves and to improve digestibility (Nguyen 2012). Phuc et al (2000) and Van Man and Wiktorsson (2002) also observed that ensiling reduced the HCN content of cassava leaves.

Taro is a food crop which provides high yield of roots (or corms) and foliage. Leaves from Taro are rich in protein, minerals and vitamins. However, taro contains high levels of oxalates which are important anti-nutritional compounds (Oscarsson and Savage 2007) which cause irritation and burning sensation in the throat and mouth on ingestion (Akpan and Umoh 2004). According to Hang et al (2011), the total oxalate ranged from 2400 to 4420 mg/100g of the DM in petioles and 2021 to 6342 in leaves. Recent research in Cambodia and Vietnam showed that the oxalate problem could be avoided by simple processing methods such as ensiling, boiling, soaking, wilting and washing (Hang and Preston 2010; Hang et al 2011, 2013; Giang and Preston 2011; Manivanh and Preston 2011).

This study was carried out to test the hypothesis that protein-enriched cassava root could partially replace ensiled taro foliage as the protein source for growing Moo Lat pigs fed ensiled cassava root as the source of carbohydrate.

Materials and methods

Location and duration

The experiment was conducted in a farmer commune in Parkhom village, Luang Prabang district Luoang Prabang Province, Lao PDR. T he site is located about 4.5 km from Luang Prabang district to the South-west; the mean daily temperature in the area at the time of the experiment from 5 ^thMarch 2016 to 27^th May, 2016 was 27^ºC (range 20-31^ºC).

Treatments and experimental design

The experiment was arranged in a completely randomized block design (RCBD) with 4 treatments and 4 replications. The treatments applied to a basal diet of ensiled cassava root (40%) and ensiled taro foliage (60%) (DM basis) were different levels of substitution of the ensiled Taro foliage by protein-enriched cassava root (PECR) (Table 1).

Animals and management

Sixteen recently weaned female pigs (Moo Lat breed) with a mean body weight of 9.8 kg were bought from a pig farm in Xayabouly Province. They were vaccinated against swine fever and treated against round worms with Ivermectin (1ml/20 kg LW), before starting the experiment.

The pigs were housed in individual pens (width 1m and length 1.2m) made from local materials (Photos 1 and 2). The pigs had free access to water through nipple drinkers. They were adapted to the pens and the feeds a week before starting the experiment. The duration of the experiment was 90 days.

Photo 1. Housing made from local materials	Photo 2. Moo Lat pig in individual cages

Feeds and feeding

Taro foliage was collected from plots established on a farm in Luang Prabang district. The leaves and petioles were chopped and ground by machine into small pieces (1-5 mm of length) and packed tightly into 30 litre plastic bags, where it was stored for 14 days before feeding.

Photo 3. Taro foliage in plastic bags	Photo 4. Ensiled Taro foliage in plastic bags

Ensiled and protein-enriched cassava root

The cassava root was bought from a farmer in Xaiyabouly province and ground by machine into small pieces (<5mm). One part was ensiled in sealed 30 liter plastic bags for a minimum of 14 days. The other part was steamed for 30 minutes, cooled then mixed with di-ammonium phosphate (DAP), yeast, and urea (0.8, 3 and 2%, all on DM basis). The mixed substrate was fermented in sealed plastic bags (anaerobic condition) for a minimum of 14 days before feeding.

Photo 5. Steamed cassava root	Photo 6. Protein-enriched cassava root (PECR) fermented in plastic bags

The diet ingredients were mixed together and fed two times per day at 6:30 am and 4:30 pm, the amount being based on an offer level of 40 g DM/kg live weight. Water was supplied ad libitum by nipple drinkers.

Data collection

The animals were weighed in the morning before feeding, at the beginning of the trial and every 14 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 at 4°C until the end of the trial when the sub-samples were mixed prior to analysis of DM, N and ash.

Chemical analysis

The chemical analysis of the feed offered and feed refusals was undertaken following the methods of AOAC (1990) for DM, N and ash.  True protein was estimated as N*6.25 in the precipitate after extraction with trichloracetic acid.

Statistical analysis

Growth rates were estimated from the linear regression of live weight (g) on time (days) in the experiment. Data for DM feed intake, DM feed conversion (FCR) and growth rate were compared using the general linear model (GLM) option in the ANOVA program of the Minitab software (Minitab 2000). Sources of variation were: levels of PECR, replicates and error. The Tukey pair-wise comparison was used to determine the differences between treatments with confidence level 95.0%. Responses in DM intake, growth and feed conversion to changing levels of PECR were estimated by polynomial regression using Microsoft Office Excel software.

Results and discussion

Protein-enriched cassava root

After 14 days of fermentation the true protein had increased from the initial value of 1.5% to 7.8% in DM, compared with the crude protein which was 14.5 (Table 2). The final level of crude protein was slightly less than that in the ensiled Taro foliage (combined leaves and petioles).

Feed intake

The response in DM intake to inclusion of PECR in the diet was curvilinear (Figure1) reaching the maximum level when PECR provided 27% of the diet protein (replacing a similar proportion of ensiled Taro foliage) (Table 3). With increasing substitution of ensiled Taro foliage by PECR, the DM intake decreased slightly. The proportion of crude protein in the consumed DM declined from 11.2% in the control diet (zero PECR) to 9.9% in DM with complete substitution of the ensiled taro foliage by PECR (Table 3).

Figure 1. Trend in DM intake of pigs feed increasing proportions of protein-enriched cassava root (PECR) replacing ensiled Taro foliage in a basal diet of ensiled cassava root

Growth rate and feed conversion

The growth of the pigs was uniform during the 84 days of the experiment (Figure 2). The effect of PECR on live weight gain and feed conversion showed similar curvilinear responses (R² = 0.97 and 0.99) as for DM intake with the optimum point of substitution by PECR at 27% of the dietary protein (Table 4; Figures 3 and 4).

Figure 2. Growth curves of the pigs on the four treatments

Figure 3. Trends in live weight gain of pigs fed increasing proportions of protein-enriched cassava root (PECR) replacing ensiled Taro foliage in a basal diet of ensiled cassava roo	Figure 4. Trends in DM feed conversion of pigs fed increasing proportions of protein-enriched cassava root (PECR) replacing ensiled Taro foliage in a basal diet of ensiled cassava root

It appeared that more than half of the dietary protein could be provided by PECR without affecting growth rate, and with only a minimal effect on DM feed conversion, as compared with the control diet in which almost all of the protein was derived from ensiled Taro foliage (Table 3). This is in agreement with the finding of Manivanh and Preston (2016) that protein-enriched cassava root could replace 16.7 % of the dietary protein provided by ensiled Taro foliage in a basal diet of ensiled banana pseudo stem fed to growing Moo Lat pigs. It is relevant to mention that the protein-enrichment of the cassava root in the experiment of Manivanh and Preston (2016) was done ‘aerobically” in contrast with the “aerobic” method used in our experiment.

Conclusions

• Anaerobic fermentation of cassava root with urea, DAP and yeast (PECR) increased the crude protein from 3.0 to 14.5% in DM; true protein was increased from 1.5 to 7.8% in DM.
  
  
• The growth rate of recently weaned Moo Lat pigs was increased from 150 to 175 g/day, when PECR replaced one third of the ensiled Taro foliage as protein supplement in a diet based on ensiled cassava root. With complete substitution of ensiled Taro foliage by PECR the growth rate decreased to 128 g/day.
  
  
• DM feed conversion was best (3.47) with 27% of the dietary protein from PECR and poorest (4.21) when PECR was the only protein supplement.

Acknowledgements

This research was done by the senior author as part of the requirements for the MSc degree in Animal Production "Improving Livelihood and Food Security of the people in Lower Mekong Basin through Climate Change Mitigation" in Cantho University, Vietnam. The authors would like to express sincere gratitude to the MEKARN II program, financed by Sida (Swedish International Development Agency) for supporting this research. We appreciate the advice received from the PhD students of MEKARN II project in the Faculty of Agriculture and Forest Resource, Department of Animal Science, Souphanouvong University, Lao PDR. We thank the farm household of Ms SengThong Silapet for providing the facilities to carry out this research.

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Received 8 January 2016; Accepted 16 September 2016; Published 1 October 2016

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