Performance of West African Dwarf sheep and goats fed varying levels of cassava pulp as a replacement for cassava peels

 R Y Baiden, S W A Rhule, H R Otsyina, E T Sottie and G Ameleke

Animal Research Institute, Box AH20, Achimota, Ghana
Byraa2001@yahoo.com
 

Abstract

Cassava pulp, a by product from the starch industry, was evaluated as a substitute for cassava peels in diets for sheep and goats.

Inclusion levels of 15% and 30% pulp in the diet had no significant effect (P>0.05) on feed intake, digestibility, growth rate, feed conversion ratio and carcass weight. Packed Cell Volume (PCV) and haemoglobin (Hb) values were significantly higher (P<0.05 and P<0.01 respectively) for sheep on the 15% (PCV 34.3%; Hb 11.8g/100ml) and 30% (PCV 34.5%; Hb 11.4g/100ml) pulp diets compared to those on the 0% (PCV 28.5%; Hb 9.00g/100ml) pulp diet.

Key words: Carcass characteristics, cassava pulp, digestibility, feed intake, growth rate, haematological values, West Africa Dwarf goats, West African Dwarf sheep.

Introduction

Cassava is primarily used in ruminant diets as an energy source. Therdchai et al (2001) reported that 94% of cassava starch was digested in the rumen, thus probably providing the energy required by the rumen microbial population. Rumen degradability of cassava peels and cassava leaves were also found to be 83% and 84% respectively (Smith et al 1991). These observations indicate that cassava as well as its by products could be very beneficial to ruminant livestock. In Ghana, one of the most common cassava by products used for ruminant feeding is the peel. Usually the peels have some cassava root tuber pieces in their lining and are from mixed varieties of cassava as described by Tuah et al (1994). The increasing demand for cassava for industrial use has however resulted in the production of large quantities of other residues, notably, the pulp. The pulp is the solid waste produced as a consequence of starch production and contains about 50-60% starch on dry matter basis (Sriroth et al 2000). During processing of cassava starch from the roots about 10-15% of cassava pulp is produced as by product. The pulp is high in fermentable carbohydrates and moisture content and low in fiber and nitrogenous compounds. Due to its rich organic nature, this residue, cassava pulp, can be an ideal substrate for micro organisms to grow and produce different products. It can thus be a nuisance to the environment when not well managed. The environmental pollution can, however, be managed if the pulp can be incorporated into livestock diets to be converted into high quality animal products for human consumption. This study therefore evaluated the effect of substitution of cassava peels by cassava pulp on the performance of West African Dwarf sheep (WADS) and West African Dwarf goats (WADG).

Materials and methods

Experimental animals

Twelve WADS aged between 4 and 7 months with an average weight of 16.7 kg (±0.7) and twelve WADG aged between 5 and 12 months with an average weight of 8.7 kg (±0.5) were used. They were dipped in an acaricide solution (Tactic, Intervet International B.V., Boxmeer, The Netherlands/Pays-Bas) against ecto-parasites, treated for internal parasites with Albendazole 10% Oral Suspension (Dutch Farm, Vet. Pharmaceuticals) and housed in individual pens at the Animal Research Institutes' Farm at Fafraha. They were assigned using stratified random sampling on age and weight basis, to one of three treatment diets such that there were four animals per feed treatment for both sheep and goats.

Experimental design

The experimental design was a 2 (species of animals) by 3 (levels of pulp) factorial arrangement for the feeding trial and a completely randomized design for the digestibility study with sheep.

Dietary treatments

The experimental diets consisted of 65% to 70% concentrate [(cassava peels ± cassava pulp) + copra cake] and 30% to 35% roughage (Stylosanthes guianensis). The diets in which cassava pulp replaced part of the cassava peels were formulated to contain about 12.5% crude protein with 70% of this amount supplied by the concentrate. The cassava pulp was supplied by the Ayensu Starch Factory. It was pressed after collection to reduce the water content and then sun dried to a moisture content of 13.9%. The cassava peels (sun dried) were obtained from cassava dough and "gari" processors near Dodowa in the Greater Accra Region, Ghana. They were coarsely milled before inclusion in the concentrate mixture. The proximate composition of the feed ingredients and the composition of the rations are given in Tables 1a and 1b.

Feeding

A 14-day adaptation period preceded the growth studies. During the adjustment period the diets were gradually introduced to the animals by reducing the level of roughage and feeding more concentrate every second day. They were put on the experimental diets fully in the third week and fed ad libitum once daily at 08:00 hours except during the digestibility trial when they were fed 90% of the previously determined maximum intake. The concentrate (copra cake + cassava peels ± cassava pulp) mixture was fed in separate containers from the roughage (Stylosanthes guianensis). Each animal had access to a mineral-vitamin lick and water at all times.

Data collection

Data were collected for nine weeks starting from the third week. Feed offered and refusals were weighed daily to measure feed intake. Daily intake of concentrate and roughage were recorded. Samples of the feed and refusals were taken daily and weekly samples bulked for laboratory analysis. Live weight was measured weekly before morning feeding. The animals were bled regularly from jugular vein weekly before feeding and the blood samples analyzed to examine the effect of the dietary treatments on some blood constituents.

Digestibility studies

The sheep were transferred into metabolism crates at the end of the growth trial for the digestibility trial. After a two week adjustment period in the crates, faeces were collected for seven days. Feed intake and faecal output were measured at the same time each day. Feed which was offered at 08:00 hours was weighed and sampled (10%) daily during the collection period and the samples kept frozen. At the end of the period the samples were thawed, bulked, mixed thoroughly and composite samples taken for analysis. Feed refusals were weighed daily, stored frozen and bulked on individual animal basis over the collection period. Sub-samples were taken at the end of the period for analysis after thawing and thorough mixing. Faeces were collected daily before feeding. The entire daily faecal output of each animal was collected, weighed, mixed thoroughly and a sample (10%) taken for daily dry matter determination in a forced-draught oven at 60ºC for 24 hours. An aliquot sample was placed in a plastic bag and stored frozen. At the end of the experiment the total faeces stored per animal were bulked, thoroughly mixed, ground to pass a 1 mm sieve and sub-sampled for chemical analysis. Dry matter (DM) and ash were determined according to AOAC (1970) method. The animals were weighed at the beginning and end of the collection period.

Carcass examination and analysis

The animals were weighed (at the end of the experiment), held overnight off feed and slaughtered the following morning. After skinning and evisceration, the rumen was cut open and the walls inspected for ulcers and scaring. Hot carcass weight was recorded and the carcass was stored in a cold room overnight. Cold carcass weight and back-fat thickness (fat depth (mm) at the 12^th rib) were recorded the following morning.

Chemical analyses

Proximate composition, dry matter (DM) and organic matter (OM) values for feed ingredients, refusals and faeces were determined using the AOAC (1970) methods. Red blood cell (RBC) and White blood cell (WBC) counts were determined using the haemocytometer. Packed Cell Volume (PCV) was estimated by microhaematocrit method and haemoglobin (Hb) concentration by the cyanmethaemoglobin method.

Statistical analyses

All data were subjected to analysis of variance using the general linear model (GLM) procedure of Minitab (2000) to determine the effect of dietary treatments on the various parameters studied. Where significant F-values for treatment effect were found, means were compared by Tukey's studentised range test.

Results

The dietary treatments had no significant effect (P>0.05) on total dry matter intake (DMI) (Table 2) by both animal species. However, intake of concentrate, roughage as well as total DMI by sheep was significantly higher (P<0.01) than the goats. Daily weight gain (DWG) and feed conversion ratio (FCR) was not affected (P>0.05) by the dietary treatments.

Haematological values in sheep and goats on the various diets are presented in Table 3. Packed cell volume (PCV) was significantly (P<0.05) higher in sheep on the 15% and 30% pulp diets compared to those on control diet as well as the goats . Total white blood cell (WBCs) counts and total red blood cell (RBCs) counts were significantly higher (P<0.01) in goats than in sheep. Haemoglobin (Hb) values were significantly (P<0.01) higher in sheep on the 15% and 30% pulp diets. Diet and animal species had no statistical effect (P>0.05) on total WBC differentials counts.

Data on diet digestibility and intake are presented in Table 4. Apparent digestibility values for DM were similar for the 0% pulp and the 15% pulp diets but relatively lower for the 30% pulp diet. The difference was, however, not significant (P>0.05). Organic matter digestibility (OMD) and DMI decreased but not significantly (P>0.05) with increasing level of pulp in the diet.

No significant differences (P>0.05) were observed in hot and cold carcass weight and fat thickness (Table 5).

Examination of the rumen lining revealed no abnormality.

Discussion

Live weight gain

Live weight gain of sheep on all the diets were relatively higher (P<0.01) than that of their goat counterparts (about twice higher). This observation could be attributed to species differences. Jabbar et al 1997 studying the benefits of Leucaena and Gliricidia as supplements for small ruminants reported that at any level of supplementation sheep grew twice as fast as goats. This performance could be attributed to better utilization of the feed by sheep than goats, thus reflecting the greater potential of the sheep for improved productivity.

Dry matter intake

Although there were no significant differences (P>0.05) in total DMI of the test diets within species, total DMI, roughage intake and concentrate intake were higher (P<0.01) in sheep than in goats. Large animals will usually eat more relative to body weight than small animals. Similar observations were made by Otchere et al (1978) and Adebowale and Taiwo (1996).

Digestibility

Dry matter and organic matter digestibilities were similar (P>0.05) for all treatments (Table 4). However, there is the possibility that higher inclusions (above 30%) of the pulp in the diet might reduce digestibility. The cassava pulp has high fiber content (Table 1a) and this could inhibit digestibility. This is because the rate of microbial colonization of a feed with high fiber content is lower compared to another with low fiber content (Silva and Ørskov 1988).

Haematological values

PCV, RBC, WBC and Hb values differ among species of animals and breeds hence the significant differences observed in this work between sheep and goats. The PCV and Hb values recorded in the present study (Table 3) for sheep on the O%, 15% and 30% pulp diets were higher than that recorded by Olayemi et al (2000) for the intensively (24.9±1.95%) and extensively (20.15±2.59) reared West African Dwarf sheep. The significant increases in PCV (P<0.05) and Hb (P<0.01) values for sheep on the 15% and 30% pulp diets as compared to 0% pulp diet could result from an element in the pulp that increased the Hb value. Total WBC counts were, however, lower than the 15.54 x10³/µl and 15.39 x10³/µl reported by Olayemi et al (2000) but fell within the range of normal values of 4x10³/µl to12x10³/µl reported for temperate breeds of sheep (Schalm et al 1986). Unlike the sheep, inclusion of the pulp in the diet had no significant effect (P>0.05) on the haematological values of the goats. The values for PCV, RBC, Hb, WBC and the percentage distribution of leucocytes recorded for the WADG on the various diets used in this work were within the range of values reported for the WADG by Daramola et al (2005).

Carcass characteristics

There was no significant difference (P>0.05) in carcass weight of sheep on the various diets and the fact that examination of the rumen revealed no abnormalities suggests that the cassava pulp could be incorporated in the diet up to 30% without adverse effect on rumen epithelial lining.
 

Conclusion

• Sheep consumed more dry matter than goats and live weight gain was about twice that of goats on all the diets.

• Goats had higher WBC and RBC values than sheep.

• Replacement of the peels with the pulp had no effect on DMI and live weight gain in both sheep and goats, but resulted in an increase in PCV and haemoglobin values in sheep. There was however, no difference in PCV and haemoglobin values when the level of pulp in the diet was increased from 15% to 30%.

Acknowledgement

The authors are grateful to the Ministry of Food and Agriculture (MoFA) for funding this work and the Ayensu Starch Factory for providing the cassava pulp. Our sincere thanks to all the technical staff of the Ruminant Division of the Animal Research Institute Katamanso station Farm, the Parasitology Laboratory and the Feed Quality control Laboratory for their technical assistance.
 

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