Previous Page Table of Contents Next Page


Preparation of cassava peels for use in small ruminant production in western Nigeria

A. A. Adegbola and O. Asaolu
Department of Animal Science
University of Ife, Ile-Ife, Nigeria


Introduction
Review of literature
Chemical composition of cassava peel and the effect of sun-drying
Cassava peel silage
References

Introduction

In the towns and villages of Western Nigeria, small ruminants (sheep and goats), are traditionally kept in backyard production systems. These animals are important sources of meat as they are cheaper to rear than cattle and require less space and shelter. Further, production requires little equipment and only small quantities of feed. They are often seen scavenging on rubbish heaps, village greens and freshly abandoned farms where they graze crop residues. The small carcass is convenient for the rural economy since the meat can easily be consumed in one day without the need for cold storage or any other form of preservation.

In this traditional management system, it is not unusual for sheep and goats to be given supplements of fresh cassava chips in the morning or evening. Cassava peels, from the processing of the roots for starch, cassava flour or tapioca and gari, are also fed. Cassava peels have not, however, been used as a basis for ration formulation in an organized fattening scheme.

Cassava meal is an important cereal substitute in Europe with Thailand, China, Indonesia and Brazil as major exporters. It was once thought that cassava chips could become an export crop from West Africa and a possible source of foreign exchange. However, given its importance in human nutrition in this zone, and the many industrial uses to which the crop is now being put, or for which it has potential, it is quite clear that cassava chips or meal will not be an economical livestock feed in West Africa. The leek of adequate technology for the production of cassava chips, the labour costs and the need for synthetic amino acids in its utilization by non-ruminants are other major constraints. By contrast, cassava peel is becoming an important byproduct and is available from the local processing of cassava root for gari as well as from the newly introduced, large-scale plants producing gari and starch. Indeed, villages with substantial numbers of small ruminants, situated near gari processing plants, have experienced a boom in sheep and goat production, especially where adequate browse is available.

The project

The purpose of this project is to see to what extent a balanced diet, based on cassava peels, can be formulated using supplements available to the livestock owner at village level or which can be easily obtained at minimal cost.

During its first year the project will:

* Develop drying and ensiling methods for cassava peels;

* Determine optimal feeding levels of cassava peels for sheep and goats;

* Determine optimum combinations of cassava peels and cocoa pods in sheep and goat diets;

* Identify important byproducts in the humid forest belt and estimate quantities available for livestock feeding.

Pending receipt of materials and equipment for the project, some preliminary work was carried out. This report presents the results of preliminary observations on the chemical composition of cassava peels, and the effects of drying and ensiling.

Review of literature

Krauss (1921) concluded that the feeding value of cassava peel was equal to that of maize. Walker (1951) fed cassava peelings to sheep and goats in Equatorial West Africa. Since then, there have been no reports in the literature on the value of cassava peels for ruminant animals from this region of the world. However, Devendra (1977) reported studies on the effects of dietary cassava chips from a sweet variety using 20-80% levels in isonitrogenous rice straw or molasses-urea diets fed to sheep. The results showed that the digestibility of dry matter in the rice straw-based diets increased significantly with the inclusion of dietary cassava. However, for all the molasses-urea based diets, dry matter digestibility decreased significantly with increasing levels of cassava inclusion. In the rice straw diets, the addition of cassava significantly increased nitrogen retention; the reverse was true for molasses-urea diets. A similar trend was observed for organic matter, crude protein, ash, ether extract, nitrogen free extract and energy digestibilities.

Since the work of Devendra, there has been additional evidence in the literature of animal responses to cassava based diets fed to ruminants (Tudor and Norton, 1982; Cockburn and Williams, 1984). Some work has been reported on the value of cassava peel as a dietary source for non-ruminant stock. Sonaiya and Omole (1977) fed cassava peel to finishing pigs and Adeyanju and Pido (1978) fed the fermented cassava peel to broiler chicks. These researchers recorded significant economic benefits in reduced feed cost and increased revenue/feed costs derived from increased levels of fermented cassava peel in the diets. They could not, however, feed the peel beyond the 20% level.

Cassava skin, which is removed on peeling, is known to contain higher levels of cyanogenetic glucosides than the root meal. In order to prevent goitrogenic and other neuropathological effects in animals, it will be necessary to process the peel if the intention is to use it as the main source of energy. Not much is known about the ability of the ruminant to digest cyanogenetic glucosides without deleterious effects. Generally, supplementation of cassava diets with high levels of sulphur amino acids, particularly cystine and methionine, and iodine, largely eliminates the goitrogenic activity due to thiocyanate production. However, amino acid supplementation is considered impractical in terms of developing an adaptable village level technology. Processing of cassava by drying or ensiling is known to reduce the content of glucosides in the product (Charavanapavan, 1944; Akinrele, 1964).

These simple processes were considered adequate for processing cassava peel as livestock feed.

Chemical composition of cassava peel and the effect of sun-drying

Results of studies in our laboratories so far indicate that cassava peel represents about 8-10% of the root dry matter. The peeling is high in the soluble carbohydrates (62%) and low in fibre (16%) with a moderate level of nitrogen (1%) (Table 1). The data of Devendra (1977) show lower N levels, higher fibre and higher soluble carbohydrates; they were using a sweeter variety than the one used at Ile-Ife. Recent work with the new, bitter varieties indicates that fresh cassava peel has a pH of 5.7 and that drying substantially increases the percent dry matter content, as well as the ash content, with little effect on the crude protein and ether extract (Table 2). Dry matter of the fresh, air-dried cassava peels was determined at 105°C for 24 hours.

Table 1. Chemical composition of cassava peel (% of dry matter).


Devendra (1977)

Adegbola (1980)

Dry matter

n.d.

13.5

Crude protein

4.8

6.5

Crude fibre

21.1

10.0

Ether extract

1.2

1.0

NFE

68.6

62.5

Ash

4.2

6.5

Ca

0.312

n.d.


0.127

n.d.

Mg

0.215

n.d.

Gross energy (MJ/kg)

2.96

1.65

Digestible energy (M/kg)

n.d.

1.03

Table 2. Preliminary data on the chemical composition of fresh and dried cassava peels (% of dry matter).


Fresh peel

Air-dried peel

Dry matter

28.5

66.25

Crude protein

5.74

5.43

Ash

7.0

15.5

Ether extract

3.25

3.5

pH

5.70


It can be assumed that drying would substantially reduce the amount of HCN liberated, as has been observed for the sliced roots by Charavanapavan (1944) and Razafimahery (1953). This reduction in HCN level will probably only take place with slow drying, since drying at higher temperatures has been proved to be less efficient. Drying took place on a concrete floor for 4 to 5 days by which time the material was beginning to darken. In addition, the lower N content of the drier material probably reflects the loss through volatilization of the released HCN.

Cassava peel silage

Small laboratory silos, in the form of plastic containers 16 cm high and 11 cm diameter, were used to study the effect of the period of ensiling and the degree of chopping and compaction of fresh cassava peels. The objective was to find out if good silage could be made by simply encouraging the villager to throw the waste peels into a container and compact them.

Observations were made on the pH, dry matter content, colour, odour, texture and the presence or absence of mould in the ensuing silage mass. These observations were made at 14, 21, 28 and 35 days after ensiling. While the tightly packed containers had 1 kg matter put into them, the moderately packed containers were filled with 0.8 kg fresh cassava peel. The dry matter content of the silages was determined by placing them in the oven for 6 hours. For the first 2 hours the oven was set at 80°C but was reduced to 70°C for the remaining 4 hours. The result from this method of dry matter determination for silage has been shown to agree with the toluene distillation method, which compensates for the loss in the volatile organic acid (Perch and Tracey, 1956).

Determination of pH was carried out by mashing the cassava peel in distilled water using five times the weight of the sample. It was allowed to stand for 2 hours, then filtered to determine the pH using the EIL pH meter model 38B.

It was observed that good silage can be made after 14 days in tightly packed containers, without loss in dry matter, with a pH of 4.35, a pleasant sweet odour (possibly from lactic acid) and no fungal growth or dark coloration. Results are best when the ensiled material is chopped into smaller pieces and not left as whole, regular peels (Table 3). Under ideal conditions, good silage is made in 2 weeks but the quality of such silage may remain uniform for only a few days (Table 4).

Table 3. Preliminary observations on ensiled fresh cassava peels (after 14 days).

 

 

Chopped

Not chopped

Tightly packed

Moderately packed

Tightly packed

Moderately packed

pH

4.35

4.7

4.4

4.8

Dry matter

34.10

20.42

33.02

23.50

Colour

Uniform light brown

Light to dark brown

Light brown

Fairly dark brown

Odour

Pleasant

Almost

Pleasant

Near vinegary

Texture

Uniformly firm

Fairly soft

Firm

Fairly firm

Other observation

No fungal growth

Some fungal growth

Slight fungal growth

Noticeable fungal growth throughout the entire mass

Table 4. Preliminary observations on ensiled fresh cassava peel (after 21 days).

 

Chopped

Not chopped

Tightly packed

Moderately packed

Tightly packed

Moderately packed

pH

4.35

4.75

4.45

4.9

Dry matter

33.70

20.9

32.65

18.5

Colour

Light brown

Dark brown

Fairly light brown

Dark brown

Odour

Pleasant

Vinegary

Fairly pleasant

Vinegary

Texture

Firm

Soft

Fairly firm

Soft

Other observation

No fungal growth

Noticeable fungal growth

Pockets of fungal growth + top spoilage

Noticeable fungal growth

Table 5. Preliminary observations on ensiled fresh cassava peels, tightly packed.

 

Chopped

Not chopped

28 days

35 days

28 days

35 days

pH

4.40

4.35

4.45

4.5

Dry matter

33.50

33.60

32.43

32.2

Colour

Light brown

Medium brown

Medium brown

Dark brown

Odour

Fairly pleasant

Less pleasant

Near vinegary

Vinegary

Texture

Fairly firm

Fairly soft

Fairly soft

Soft

Other

Slight fungal growth

More fungal growth

Top spoilage

Larger pockets of fungal growth

However, when left for 4 and 5 weeks (Table 5), the silage tends to become darker and the odour less pleasant. Softness increases and there is more fungal growth, even when chopped into smaller particles and tightly compacted. Unchopped, moderately packed peels turned to rotten masses in 4 to 5 weeks.

These observations are only indicative of the qualities of silage obtainable using simple technology which can be adapted to the village level. Following the observations, an attempt was made to ensile a large quantity of chopped, tightly packed, cassava peels. A 200 litre drum was filled with cassava peels, covered with thin plastic sheeting and weighed down with heavy stones to ensure compaction. After 2 weeks the silage was opened. It was light brown in colour, sweet smelling and free from fungal growth. However, the ensiled silage darkened within an hour of opening and after about 2 hours it had turned very dark. This browning effect may be due to oxidation of some of the organic acids produced during ensiling. Ohochuku and Ballantine (1983) have indicated that the compounds responsible for the objectionable (vinegary) odour in the fermented cassava mass include butanoic, propanoic and acetic acid, butanoic acid being the most offensive.

When the ensiled material was offered ad libitum to four sheep in a preliminary feed trial, it was largely rejected, perhaps due to lack of familiarity. We have previously observed sheep and goats relishing sweet-smelling cassava peel silage on a disposal dump near a gari processing factory. On the other hand, the rejection may be due to the presence of hydrolysed HCN as the silage was not drained. Charavanapavan (1944) has indicated that "stale" cassava can be more toxic than the fresh and there may be a need to allow the hydrolysed HCN to drain away.

From these observations it appears that in order to make good silage from cassava peels, care must be taken to ensure good compaction and adequate drainage, and to prevent rapid oxidation or the formation of organic acids after ensiling.

References

Adeyanju S A and Pido P P. 1978. The feeding value of fermented cassava peel in broiler diets. Nutrition Rep. International 18:79-86.

Akinrele I A, 1964. Fermentation of cassava. Journal of the Science of Food and Agriculture 15:589-594.

Charavanapavan C, 1944. Studies in manioca and lima beans with special reference to their utilization as harmless food. Tropical Agriculture 100:164-168.

Cockburn J E and Williams A P. 1984. The simultaneous estimation of the amounts of protozoa!, bacterial and dietary nitrogen entering the duodenum of steers. British Journal of Nutrition 51:111-132.

Devendra C, 1977. Cassava as a feed source for ruminants. In: Nestle B and Graham M (eds), Cassava as animal feed. IDRC, Canada. 107-119.

Krauss F G. 1921. Production of starch on a small commercial scale from root crops and corn. Hawaii Agric. Expt. Sta. 55.

Perch and Tracey, 1956. Modern methods of plant analysis 1:3.

Ohochuku N S and Ballantine J A, 1983. Fermented cassava: odour active components. Journal Agriculture Food Chemistry 31(6):1386-1387.

Sonaiya E B and Omole I A, 1977. Cassava peels for finishing pigs. Nutrition Rep. International 16(4):479-485.

Tudor G D and Norton B W. 1982. The nutritive value of cassava for cattle. In: Proceedings of Australian Soc. Animal Production 14:599.

Walker A, 1951. Un aliment de famine: l'ecorce de manioc. Rev. International Bot. Appl. 31:542.


Previous Page Top of Page Next Page