Cassava pulp as livestock feed; effects of storage in an open pit

Phanthavong Vongsamphanh, Viengsakoun Napasirth¹, Sangkhom Inthapanya² and T R Preston³

Department of Livestock and Fisheries, Ministry of Agriculture and Forestry
PO Box 6644 Vientiane, Lao PDR
ptvkivor@yahoo.com
¹Faculty of Agriculture, National University of Laos, Nabong Campus, P.O.Box 7322, Vientiane, Lao PDR
²Souphanouvong University, Luang Prabang, Lao PDR
³Center for Research and Technology Transfer, Nong Lam University, Ho Chi Minh City, Vietnam

Abstract

Samples were taken from an uncovered  pit (250*50m area; 7 m deep) in which cassava pulp, the byproduct from cassava root starch extraction, had been stored over a 4 year period (2011-14).  A sample taken at 2.5m depth was incubated with urea, cassava leaf meal and rumen fluid in an in vitro rumen  fermentation and compared with fresh cassava root as a control.

The upper 50 cm had rotted due to exposure to air and rain, but samples from 0.5 to 7m revealed that these were satisfactorily ensiled with pH values in the range 3.2 to 3.5.  Gas production amd DM mineralization values after 24h incubation of the sample taken at 2.5m depth indicated that the pulp was only slightly inferior (<9%) to fresh cassava root as an energy feed resource for ruminants.

Key words: cassava root, cattle feed, gas production, pH, methane, starch processing

Introduction

The Lao-Indochina Group Public Company at Nashaw village, Pakngum District, Vientiane, processes up to 100.000 tonnes per year of cassava roots into starch for export. During the  6-7 month harvest season from October to March-April (the dry season in Lao PDR) this amounts to 480 tonnes of roots daily. The byproduct remaining after starch extraction, known as cassava pulp, represents from 10 to 15% of the original weight of fresh roots (Sriroth et al 2000). Over the past 4 years, very little of the cassava pulp was bought by farmers and almost all of it had been stored in a pit adjacent to the factory, which had not been covered or protected in any way.

As the first step in a study to evaluate the potential feeding value of the stored pulp, the site was visited on July 10, 2014. As the pit was not covered, the upper surface of the stored material had rotted due to accumulation of rain falling during the wet season (Photo 1). However, A sample taken at a depth from the surface of 50 cm was perfectly ensiled with a pH of 3.5.

Photo 1. The pit containing the cassava pulp; photo taken in the rainy season	Photo 2. Taking the samples in the pit

Photo 3. Inserting the PVC tube to reach the bottomof the pit	Photo 4. Separating the samples from the core taken from the PVC tube

It was hypothesized that if the rest of the pulp in the pit had similar characteristics to the observed sample then it would be a suitable basal diet for the intensive fattening of cattle, for which there is an attractive market (>USD 2.00/kg live weight) in Lao PDR for export to China, Thailand and Vietnam.

Materials and methods

Testing the pH and dry matter content of the pulp over the whole range of depth (0.5 to 7.0m)

Further tests were done on 16 July taking consecutive samples as far as the bottom of the pit using a 10cm diameter PVC tube 8m long (Photo 2). The pH and the DM content were determined by standard methods (AOAC 1990).

In vitro gas and methane production

A sample of the ensiled cassava pulp was taken at 2.5m depth to determine in vitro gas production according to the method developed by Sangkhom et al (2011). The sample had a pH of 3.5. In the in vitro test it was compared with fresh whole cassava root. Urea and cassava leaf meal were added to both substrates (Table 1). There were two replicates of each of the treatrments (cassva root vs cassava pulp).

Fresh cassava root was purxhased from the market and chopped into small piece around 1-2 cm of length, then ground (1mm sieve) by machine.  The cassava leaf was collected in the farm of Souphanouvong University; Luang Prabang and chopped into small pieces around 1-2 cm, then dried in an oven at 100°C for 24h and ground (1mm sieve) by machine.   

Representative samples of the substrates (12 g DM) were put in each incubation bottle, after which were added 0.96 liters of buffer solution (Table 2) and 240 ml of rumen fluid (obtained from a recently slaughtered buffalo in the local abattoir), prior to filling each bottle with carbon dioxide. The bottles were incubated at 38ºC in a water bath for 24h.

Gas production was measured from 0-6h, 6-12h, 12-24h. Methane was measured in the gas from the 12-24h collection using a Crowcom infra-red meter.

Statistical analysis

Data for gas prodution and methane in the gas were analysed by the GLM option in the ANOVA program of the Minitab (2010) sotfware. Sources of variation were treatments, replicates and error. Regression equations were derived using Microsoft Excel software.

Results and discussion

All samples taken from the pit had a consistent pH below 3.5 and appeared to be perfectly stable as silage (Figures 1 and 2). Due to compression of the pulp inside the tube, as this was forced to the bottom of the pit, the recovered samples most probably represented material over the whole range of depth of 0.5 to 7.0m. It is also probable that the true DM content is between 20 and 25%. This can only be checked when the full face of the pit is opened.

Figure 1. Changes in dry matter content of the pulp at increasing depth in the pit	Figure 2. Changes in pH of the pulp at increasing depth in the pit

Figure 3. Gas production from cassava pulp and cassava root supplemented with urea and cassava leaf meal

Total gas production over 24 h tended (p <0.18) to be less with the pulp than with the whole cassava root (Table 2; Figure 3), however, the overall diference was only 9% ; there were no differences in DM mineralized which were less than 1% during this period. Thus it can be expected that the energy feed value of the ensiled pulp will be only slightly less than that of the whole fresh root. The methane content of the gas produced between 12 and 24h did not differ between the pulp and root samples.

The crude protein in cassava pulp is very low. Reported values are 1.55 to 2.6% in DM (Sriroth et al 2000; Suksombat et al 2007). However, it is rich in starch; 69% in DM according to Sriroth et al (2000). This makes it suitable as the energy component of an intensive feeding system for fattening cattle. It would need to be supplemented only with urea, a source of roughage and bypass protein and minerals, as has been demonstrated for other low-protein, carbohydrate-rich tropical feeds such as molasses (Preston 1971; Ffoulkes and Preston 1978))and sugar cane (Preston et al 1976).

Conclusions

• Cassava pulp was ensiled naturally (pH 3.5) when stored in an uncovered pit for up to 4 years.
  
  
• Gas production amd DM mineralization values after 24h fermentation in an in vitro incubation showed it to be only slightly inferior (<10%) to fresh cassava root as an energy feed resource for ruminants.

References

AOAC 1990 Official methods of analysis. 15th ed. AOAC, Washington, D.C.

Ffoulkes D and Preston T R 1978 Cassava or sweet potato forage as combinedsources of protein and roughage in molasses based diets: effect of supplementation with soybean meal. Tropical Animal Production, Voume 3, Number 3 pp186-192 http://www.utafoundation.org/UTAINFO1/TAP/TAP33/3_3_1.pdf

Inthapanya S, Preston T R and Leng R A 2011 Mitigating methane production from ruminants; effect of calcium nitrate as modifier of the fermentation in an in vitro incubation using cassava root as the energy source and leaves of cassava or Mimosa pigra as source of protein. Livestock Research for Rural Development. Volume 23, Article #21. http://www.lrrd.org/lrrd23/2/sang23021.htm

Minitab 2010 Minitab Statistical Software, Release 16.1.1 for Window.  (Minitab Inc. State College PA, USA)

Preston T R 1971 Quantitative aspects of animal protein production from NPN in ruminants Source:FAO/IAEA. Tracer studies on non-protein nitrogen for ruminants. publications\Preston1971(IAEA).pdf

Preston T R, Carcaño C, Alvarez F J and Gutierrez D G 1976 Rice polishings as a supplement in a sugar cane diet effect of level of rice polishings and of processing the sugar cane by derinding or chopping. Tropical Animal Production. Volume 1, Number 3 pp 1-14 http://www.utafoundation.org/UTAINFO1/TAP/TAP13/1_3_1.pdf

Sriroth K, Chollakup R, Chotineeranat S, Piyachomkwan K and Oates C G 2000 Processing of cassava waste for improved biomass utilization. Bioresource Technolology 71(1):63-69.

Suksombat W, Lounglawan P and Noosen P 2007 Energy and protein evaluation of five feedstuffs used in diet in which cassava pulp as main energy source for lactating dairy cows. Suranaree Journal of Science and Technology Volume 14, Number 1, pp 99-107

Tilley J M A and Terry R A 1963 A two stage technique for the in vitro digestion of forage crops. Journal of the British Grassland Society 18 : 104.

Received 25 August 2014; Accepted 29 August 2014; Published 5 September 2014

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