Quantitative biology of cassava varieties suitable for livestock feeds
Biochemical aspects of cassava utilization for livestock
Low cyanide cassava varieties
References
J.E. Okeke
Cassava improvement in Nigeria is reviewed to highlight research on the development of varieties with such desirable characteristics as: (a) resistance to pests and diseases, (b) high dry matter and starch content, and (c) high dry matter yields for food, animal feeds and industry. The initial approach was to develop varieties that were highly tolerant or resistant to primary biotic stresses, notably cassava bacterial blight (CBB) and cassava mosaic virus (CMV). Subsequently, screening for varieties with high photosynthetic efficiency and important morphological determinants of yield, and later crossing and selecting for high yield and high dry matter content resulted in over 80 recommended improved varieties currently available to Nigerian farmers. Varieties TMS 50395, TMS 91934, NR 8267 and NR 8212 were identified as suitable for animal feeds because of their high dry matter yield, high percent peel and high fibre content. However, high total dry matter yielders with low cyanide are preferred for animal feed.
Cassava improvement in Nigeria started about 1940 (Umanah 1977) with the collection and introduction of superior germplasm for improved yields and resistance against the cassava mosaic virus. The Gold Coast Hybrid (GCH 7) was the first recorded superior material with an average yield of 9 t/ha and a yield improvement of 28 percent over native varieties. Major improvements have since been made over the years, with the development of varieties which yield 2-3 times higher than native varieties.
Research in Nigeria has emphasized the development of high-yielding varieties with good food quality characteristics and resistance/tolerance to pests and diseases. Advances were made from the 1970s with the release of high-yielding varieties which were also resistant to the endemic diseases of native varieties, the cassava mosaic disease (CMD) and cassava bacteria blight (CBB). Selection parameters included starch and dry matter contents, HCN levels and yields of various food products. The heritability of harvest index which is the ratio of root weight to the weight of the entire biomass, was also emphasized during selection. Physiological and developmental processes that determine yield were also recognized in selection. Most of the recommended varieties are high yielders with high harvest indices (0.6-0.7) and less than profuse top growth. However, some of the varieties have partitioning mechanisms equilibrating top and root growths. Such varieties have been identified as good sources of carbohydrates and proteins for animal feeds.
Fresh cassava roots are fed directly to hogs, and for some decades, cassava has been the main carbohydrate base for swine nutrition in Nigeria. Modebe (1963) formulated cassava-based pig rations for exotic breeds in Nigeria, and whole life cycle swine feeding systems using cassava roots have been standardized (Gomez 1977). Until recently, poultry and other classes of livestock were raised exclusively on maize or grain carbohydrate-based feeds. The scarcity and high cost of maize have brought into sharp focus the value of utilizing cassava in the livestock production industry because of special inherent attributes such as high energy yields and continous availability. The demands for cassava roots for food, feed and industry have increased rapidly in recent times, resulting in a changing emphasis in the improvement of the crop. Cassava is a highly efficient plant. The entire top growth, stem, petiole and leaf blades, contain up to 17% crude protein (Mantaldo 1977). A Japanese factory in Thailand exploits this factor by pelletizing the top growth and exporting it to Japan as a protein source for use in animal feeds (Booth and Wholey 1978). Crude protein content of leaf blades ranges from 24-26 °/0 in Nigerian cassava varieties (Okeke 1978). Müller et al. (1974) reported a crude protein content of 23.3% with a good amino acid profile which was low only in methionine and cystine.
The high levels of HCN in Nigerian cassava varieties (150-400 mg/kg) is a major constraint in using cassava meal in animal feed formulation. Oke (1969) reviewed the nutritional implications of HCN in animal feeds and highlighted the toxicity problems. High-yielding cassava varieties with low rates of detoxification during processing would be ideal for the livestock industry. Cassava roots are low in crude protein (2.0-3.2 °/0) most of which is in the peel. As unpeeled tubers are grated for cassava root meal (CRM), variability in peel content of tubers among varieties is exploitable for animal feeds.
The characteristics of currently recommended improved varieties favoring their use in animal feeds are presented in this paper.
The entire cassava biomass is valuable to the livestock industry. The top growth is milled or pelleted as a protein source while the underground root tubers provide high energy carbohydrate. Wide variability in shoot morphology exists among cultivars. There are profusely branching types as well as nonbranching or sparsely branching types. There are also tall varieties (> 1.5m) and short varieties (< 1m) and the point of interception of radiation in a competitive environment is known to correlate with total dry matter production (Okeke 1979). These considerations formed the basis for the selections from recommended improved varieties presented in table 1. In this table, TMS 30572 is most widely adopted in Nigeria because of its good food quality characteristics, disease resistance, and yield superiority over native cultivars. It does not, however, compare favorably with the other four varieties in terms of total dry matter available for livestock and the low performance in this regard, appears to be associated with its low height and less than profuse branching habit.
Table 1. Quantitative characteristics of cassava varieties suitable for livestock feeds
|
Characteristics |
Cassava variety |
|||||
|
TMS |
TMS |
NR |
NR |
TMS |
||
|
50395 |
91934 |
8267 |
8212 |
30572 |
||
|
Shoot morphology |
||||||
|
|
Branching order |
5th |
5th |
4th |
4th |
3rd/4th |
|
|
Dominant lobe no. |
7 |
3 |
7 |
7 |
7 |
|
|
Canopy height (cm) |
>1m |
>1m |
>1m |
>1.5m |
>1m |
|
Dry matter yields (t/ha) |
||||||
|
|
Roots |
8.9 |
7.9 |
8 |
9.8 |
6.1 |
|
|
Tops |
10.8 |
9.6 |
9.4 |
8.2 |
5.2 |
|
|
Total biomass |
19.7 |
16.5 |
17.4 |
18.0 |
11.3 |
Cassava substitutes for maize in livestock feeds, mainly for dairy and beef cattle, goats, pigs, and chicken up to 40 percent in the European Economic Community (Thanh and Lohani 1978). A 60 percent substitution with good balance in other nutrients was reported by Omole (1977) who also highlighted toxicity problems. Ngoka et al. (1984) substituted cassava root meal (CRM) for maize at levels 0-50-75- 100 % in diets for layers, broilers and breeder stock, and recommended substitution up to 75 percent with appropriate processing to detoxify the CRM.
Thus, the toxicity caused by the presence of the cyanogenic glucosides, linamarin and lotaustralin, in cassava is well recognized. Oke (1969) postulated that the affinity of released HCN for metal ions such as copper and iron could pose problems with enzyme systems in chickens. The use of dried chips of high cyanide varieties for chicken, for example, has proved disastrous in feeding trials. A detoxification regime of grating to release bound cyanide, fermentation for 48 hours, dewatering and drying to 15% moisture was necessary to reduce total cyanide from 360 mg/kg to the safe level of 1520 mg/kg (Okeke 1980).
The use of low cyanide cassava varieties (<5mg HCN/100g) rather than the more dominant high cyanide (>15mg HCN/100g) varieties for feeds or food would eliminate fermentation in processing. Tubers of low cyanide cassava could be chipped or crushed and dried for use. Native low cyanide cassava varieties are inherently low-yielding and highly susceptible to disease attack. However, the consistently high performance of variety TMS 4(2) 1425 over time and space has shown that it is possible to improve low cyanide cassava for high yields and tolerance/resistance to pests and diseases. Variety TMS 4(2) 1425 has about 3.1 mgHCN/100g and yields over 20t/ha (IITA 1986). The top growth is however relatively sparse. The ideal cassava for livestock would be the highest aggregate yielder of total dry matter with minimum HCN content.
Booth, R.H., and D.W. Wholey. 1978. Cassava processing in Southeast Asia Pages 711 in cassava harvesting and processing, edited by A. Ghoninard, J. H. Cook and E. J. Weber. CIAT/IDRC-114e.
Gomez, G. 1977. Utilization of cassava-based diets in swine feeding. Pages 65-71 in Cassava as animal feed. Proceedings, Cassava as Animal Feed Workshop, University of Guelph, 18-20 April 1977, Canada. IDRC-095e: Ottawa.
IITA (International Institute of Tropical Agriculture). 1986. Annual report. IITA, Ibadan, Nigeria. 91 pp.
Müller, Z., K.C. Chou, and KC. Nah. 1974. Cassava as a total substitute for cereals in livestock and poultry rations. World Animal Review 12(1): 19-24.
Modebe, A.N.A. 1963. Preliminary trial on the value of dried cassava for pig feeding. Journal of West African Science Association 7: 127- 133.
Montaldo, A. 1977. Whole plant utilization of cassava for animal feed. Pages 95-105 in Cassava as animal feed. Proceedings, Cassava as Animal Feed Workshop, University of Guelph, 18-20 April 1977, Canada. IDRC-095e: Ottawa.
Ngoka, D.A., L.S.O. Ene, A.O. Okpokiri, and S.O. Odurukwe. 1984. The use of cassava root meal as energy substitute for maize in poultry diets. Research Bulletin No. 2 of the NRCRI, Umudike, Nigeria
Oke, O.L. 1969. The role of hydrocyanic acid in nutrition. World Review of Nutrition end Dietetics 11: 170-198.
Okeke, J.E. 1978. Concentration of nutrients in plant parts and growth relationships. PhD thesis, University of Ibadan, Nigeria.
Okeke, J.E. 1979. Evaluation of agronomic traits in six Nigerian cassava varieties on representative ultisol and alfisol of southern Nigeria. Journal of Root Crops 5(1 & 2): 25-31.
Okeke, J.E. 1980. Studies in the use of cassava products in poultry feeds. Pages 4243 in NRCRI annual report. Umudike, Nigeria.
Omole, T.A. 1977. Cassava in the nutrition of layers. Pages 51-55 in Cassava as animal feed. Proceedings, Cassava as Animal Feed Workshop, University of Guelph, 18-20 April 1977, Canada. IDRC-095e: Ottawa.
Oyenuga, V.A. 1968. Nigeria's food and feeding stuffs: their chemistry and nutritive value. Ibadan University Press.
Thanh, N.C., and B.N. Lohani. 1978. Cassava chipping and drying in Thailand. Pages 21 -25 in Cassava harvesting and processing, edited by E.J. Weber, J. H. Cook and A. Ghoninard. IDRC-114e: Ottawa
Umanah, E.E. 1977. Cassava research in Nigeria before 1972. Pages 137-141 Proceedings, Fourth Symposium of the International Society for Tropical Root Crops, edited by J. Cock, R MacIntyre and M. Graham. IDRC-080e: Ottawa
