Nutrient characterization of cassava plant meal and its utilization by broiler chickens in the tropics

E O Akinfala, O Matanmi and J A Tinuala

Department of Animal Sciences, Obafemi Awolowo University, Ile Ife, Nigeria
oakinfala@yahoo.com   or   akinfala@oauife.edu.ng

Abstract

The study was designed to determine the proximate composition, insoluble carbohydrate fraction, hydrogen cyanide, metabolicable energy and minerals composition of cassava plant meal (CPM) and to evaluate the utilization of the CPM as a replacement for maize by broiler chickens.  One hundred and eight 7- day old broiler chickens of hybro strain were used for the study that lasted for seven weeks.  The birds were randomly distributed into three experimental diets with three replicates per treatment in a completely randomized design.  Diet 1 that served as the control was maize based.  Diets 2 and 3 had 25% and 50% of maize in diet 1 replaced with CPM respectively.  The CPM contained unpeeled cassava tubers/roots mixed with leaves and tender-stems. The ratio of unpeeled tubers to leaves + tender stems was 2.5:1, while the ratio of leaves to tender-stems was 5:1.  These ratios were used to make CPM have about 9.0% crude protein.  Chemical analysis showed that crude protein of (9.40%) CPM was close to that of maize (11.7%) while the energy values were 2,857lcal/kg and 3,200kcal/g for CPM and maize respectively.  The CPM also had high amount of insoluble carbohydrates and minerals such as manganese, magnesium, zinc, calcium, copper, iron and phosphorous were higher in CPM than maize.

The performance results showed that average final body weight per bird was (P< 0.05) highest for birds in diet 1 and lowest for bird in diet 3. Average daily weight gain was affected (P< 0.05) with the inclusion of CPM in the diets with diet 1 having the correspondence highest value and diet 3 the lowest. The results of the carcass evaluation showed that carcass and organs weights were (P< 0.05) affected by dietary treatments.  The economy of production showed that replacing maize with CPM in broiler diets could reduce cost of production.

 It can thus be concluded from this study that the CPM could be included in the diet of broiler chicken to replace 25% of maize without any serious effect on the performance, carcass quality and economy of production.

Key words: Carcass quality, economy of production, feeding, maize, poultry

Introduction

Nigeria, which produces an estimated 34 million metric tons of cassava annually, is the leading producer of cassava worldwide (FAO 2004a).  There had been several studies by many scientists on the use of cassava for livestock feeding especially poultry.  Most of these studies (Akinfala et al 2002; Aderemi et al 2000; Matanmi et al 2005) were propelled by the escalate price of maize in Nigeria in recent years because of the increasing pressure on the use of maize by human population.

Previous studies on the use of cassava in the diets of poultry either centered on the use of the flour or peel or leaves (Tewe and Egbunike 1992; Ogbonna 1991; Job et al 1980).  Besides, most of these studies confirmed the suitability of cassava flour or peel to replace maize partially in the diets of poultry.  The replacement of maize with cassava flour was reported to be economical.  These findings appear to have been overtaken by events and recently in Nigeria, cassava has been attracting interest as an industrial crop having found various uses in the starch, pharmaceutical, bread and biscuit industries.  This has made the price of cassava flour to be on the increase thereby making its use to replace maize in the diets of livestock unattractive economically.  In this study, attempt was made to reduce the flour content in the diet considerably by adding more of peels, leaves and tender stems.  Most of these by products from cassava especially peels, leaves and tender-stems are under utilized as they are often left to rot away after harvest on farms and homesteads where cassava is grown in Nigeria

Earlier research effort on the use of cassava plant meal (unpeeled tuber + leaves + tender-stems) as a replacement for maize in the diet of broiler chicken (Akinfala et al 2002) showed the potential of cassava plant meal as a feedstuff. Findings from the study of Akinfala et al (2002) stimulated this current effort of using cassava plant meal in the diet of broiler chicken until market age.

Hence, the objective of this study was to characterize some of the nutrients in cassava plant meal and evaluate how well the nutrients in it are utilized by broiler chicken.

Materials and Methods

Collection and processing of test ingredients

Fresh cassava tubers, leaves and tender stems from harvested cassava plant were collected from the Obafemi  Awolowo University Teaching and Research Farm, Ile Ife, Nigeria.  Following the processing protocol of Akinfala et al (2002), the unpeeled cassava tubers were washed and sliced into pieces.  The tender stems were chopped with the aid of a cutlass.  The unpeeled tubers, leaves and tender stems were sun-dried on concrete floor for about 7 to 10 days with daily turning depending on the intensity of the sunlight.  They were then milled separately using grinding machine.  Cassava plant meal was prepared, which had the ratio of 2.5:1 of the unpeeled tubers to leaves and tender stems, while the ratio of leaves to tender stems was 5:1.  These combinations were adapted from Akinfala et al (2002).

Experimental birds

One hundred and eight 7- day old broiler chicks of hydro strain were used.  The birds were raised on a deep litter system.  The birds were randomly distributed into three experimental diets with each diet having three replicates. Routine vaccinations and medications were followed during the period of the study.  The birds were fed and watered ad libitum. The birds were given a starter feed for four weeks and finisher feed for three weeks. The feeding troughs were cleaned and supplied with fresh feed every day. The watering troughs were equally washed and supplied with fresh clean water every day. The birds were weighed on weekly basis to determine growth parameters such as weight gain and feed to gain ratio.   

Experimental diets

Three experimental diets were formulated at both the starter and finisher phases respectively.  Diet 1 was maize based and served as the control.  Diets 2 and 3 had 25% and 50% of maize in diet 1 replaced with cassava plant meal (CPM) respectively (Tables 1 and 2).

Carcass evaluation

At the end of the seven weeks of growth study, six birds per treatment were isolated for the purpose of carcass evaluation.  They were starved for 12 hours, weighed and their heads were severed with knife through the cervical vertebrae at the base of the occipital bone.  The drainable blood from the birds after slaughter was collected into the jar of known weight and the blood collected on individual basis was weighed. Slaughtered birds were defeathered and the feathers were collected and weighed.  The head was removed completely and the weight taken.  The shanks were removed at tibio-tarsal joints, the weights were taken.  Lateral cuts were made through the rib-head to the pectoral girdle and the breast separated by tilting up anteriorly.  Vents were removed with the intestines.  The carcass and visceral organs were weighed.  The thighs were dislocated by bending dorsally at the ileo-femoral joints.  Lungs and kidneys were carefully scrapped out with forceps and weighed.  The various part of the alimentary canals; small intestine, large intestine and caeca were separated and their weight taken.  Organs including the crop, liver and spleen were removed and weighed.  The whole gizzard and the proventiculus were carefully removed and weighed.  The carcass weight was then determined to obtain dressing percentage.

Chemical and statistical analyses

The proximate composition of the test ingredients and experimental diets was determined using the method outline by AOAC (1995).  The insoluble carbohydrate fractions of the cassava plant meal were analysed by methods outlined by Georing and Vansoest (1970). The residual cyanide in the cassava plant meal was analysed by methods outlined by ISO (1975). The energy content of the test ingredients and experimental diets was determined using bomb calorimeter. All data obtained were analysed using analysis of variance (SAS 2000) and means were compared using Dunca’s multiple range test at 5% level of significance.

Results

Table 3 showed the nutrient composition of cassava plant meal (CPM) and maize.  The crude protein of CPM was 9.40% while that of maize was 11.7%.  The crude fibre (4.96%) and ash (5.28%) values were higher than that of maize.  The ether extract (3.50%) and Nitrogen free extract (67.9%) values were lower expectedly than that of maize. The results of minerals content of CPM showed that minerals such as Mn, Mg, Cu, Ca and Fe were higher in CPM than maize,  while Zn and P were higher in maize then CPM.

Proximate composition of experimental diets at starter and finisher phases

The proximate composition of the experimental diets at starter phase is shown in Table 4 while that of finisher phase is shown in Table 5.  The dry matter content of the broiler starter diets was fairly constant ranging from 91.6% in diet 2 to 92.5% in diet 1.  The crude protein that ranged from 20.8% to 21.8% decreased with the inclusion of cassava plant meal to replace maize.  The crude fibre was highest for diet 3 (7.50%) and lowest for diet 1 (5.80%). The crude fibre also increased with the inclusion of CPM in the diets.

As shown on Table 5, the crude protein value of the experimental diets at finisher phase ranged from 18.9% in diet 3 to 19.7% in diet 1.  The crude fibre value which increased with the inclusion of CPM in the diets was highest in diet 3 (8.30%) and the lowest occurred in diet 1 (6.00%).  The ether extract increased with the inclusion of CPM with highest value occurring in diet 2 and lowest value in diet 1.  The ash content had the highest value in diet 1 and lowest value in diet 2.

Performance characteristics

As shown in Table 6, the average final body weight was influenced by the dietary treatments.  Diet 1 had highest value (1640g) while (P<0.05) diet 3 had the lowest value (1360g).  The average daily weight gain decreased (P<0.05) among the dietary treatment with increasing level of cassava plant meal (CPM).  The feed to gain ratio decreased (P<0.05) with the increasing level of CPM.  Birds on diet 1 had the best feed/gain ratio (2.01) while those in diet 3 had he least (2.49).

Carcass evaluation

Table 7 showed the carcass evaluation of the experimental birds.  The results obtained showed that the dietary treatments affected (P<0.05) the carcass weight with diet 1 having the highest value (1150g) and diet 3 had the lowest value (883g).  The organs weights were equally affected (P<0.05) by the dietary treatments.  Expectedly diet 1 gave the best value in all the parameters monitored except small intestine while diet 3 gave the least values.

Economy of production

The cost implication of using cassava plant meal to replace maize in the diet of broiler chicken was evaluated and as shown in Table 8, feed cost per kg of diet was highest in diet 1 ($0.32) and lowest for diet 3 ($0.27).  Cost of production per bird was highest in diet 1 ($3.13) and lowest for diet 3 ($2.94).  The profit per bird for highest in diet 2 ($1.64) and lowest for diet 3 ($1.34)

Discussion

The observed value of 90.60% dry matter for cassava plant meal was lower than the value reported by Akinfala et al (2002).  The same thing was applicable to Nitrogen free extract.  However, the value for crude protein, crude fibre and ether extract were similar to the values reported by Akinfala et al (2002) and  Akinsuyi (2003).  The ash content was higher than value reported by them. The cassava plant meal appeared to be a fibrous ingredient because of values obtained for the non-soluble carbohydrate fraction such as acid detergent fibre, neutral detergent fibre and lignin.  The cyanide level of cassava plant meal was low, this may be due to variety of cassava plant and processing technique used (Tewe 1991).  Sun drying has the potential of reducing cyanide level of potentially toxic variety to a safe level of about 100ppm (Tewe and Egbunike 1992).  Though, the minerals level in CPM was higher than that of maize in this study, findings from this study appeared not confer any advantage nutritionally to the animals in performance and carcass evaluation. However, further research efforts may be needed to throw more light to this assertion.

The diets formulated were adequate in crude protein according to the recommendation of Balogun and Fetuga (1990).  Although, cassava plant appeared to be similar to maize in proximate composition, it’s inclusion to replace maize in this study did not justify this similarity.  The growth rate of the birds decreased and feed to gain ratio was negatively affected as the proportion of cassava plant meal increased in the diets.  This was similar to the findings of Akinfala et al (2002) that the nutrients in whole cassava plant were apparently used less efficiently for growth than the nutrients in maize.  This may be because the protein provided by cassava plant meal was of rather inferior quality compared to maize. Besides, the synthetic DL-methionine level in the CPM based diets might not be enough to bring about the desired growth in the animals, because part of it might have been used to detoxify the residual hydrogen cyanide to the more innocuous thiocyanate (Tewe and Egbunike 1992;Tewe 1994). There were no health problems in the experimental birds even when cassava plant meal replaced 50% of maize but growth rate was impaired by 8% and 18% on the 12.5 and 25% cassava plant meal diets respectively and feed conversion was impaired by 10% and 20% on 12.5 and 25% cassava plant meal respectively.  This was an improvement on the results obtained by Akinfala et al (2002). In contrast to this, the growth rate and feed conversion efficiency were poorer in this study compared to the findings of Akinfala et al (2002). This may be due to higher fibre content of the diets in this study compared to Akinfala et al (2002).  The proximate composition, which showed the crude fibre to range from 6.00 – 8.30%, is high and this may be the reason for the observed  performance characteristics of the experimental birds in this study.

The results of carcass evaluation followed the trend of performance of the experimental birds.  There appeared to be a relationship between the body weight of the experimental bird and

weights of the organs. As the level of CPM in the diets increased, the dressed weight and organs weight decreased with the exception of small intestine and ceacum.  This may be due to higher fibre content of CPM compared to maize and this agreed with the findings of Akintola and Abiola (1999).  The weight of the ceacum increased as the proportion of CPM in the diets increase.  This trend has been attributed to high fibre content in the given diet.  According to Akintola and Abiola (1999), increase in fibre content of diet may lead to heavier caeca weight.  The probable reason for this might be due to increased microbial activity in the caeca, due to undigested nutrient at the stomach as a result of higher fibre content of CPM based diets.  The higher small intestine weight of birds on CPM based diets in this study may be attributed to reasons applicable to caeca weight.  The inclusion of CPM to replace maize was economical when included at 12.5% of the formulated diet or when used to replace 25% of maize in the formulated diet.  This may be due to low cost (processing cost) of leaves + tender stems and peels of cassava.  Because on most farms, they are left unutilized after harvesting of cassava tuber.

Conclusion

• The results of this study showed that sun-dried cassava plant meal can be included in the diets of broiler chickens from seven weeks to replace 25% and 50% of maize in their diets without health problem, but a reduced growth rate, carcass weight and organs weight will occur.  The economy of production showed that when CPM replaced 25% of maize in the diet, more profit could  generated in the production system.

References

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Received 3 July 2011; Accepted 15 September 2011; Published 4 November 2011

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