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close this bookBioconversion of Organic Residues for Rural Communities (UNU, 1979)
close this folderPerspectives on bioconversion of organic residues for rural communities
View the document(introduction...)
View the documentIntroduction
View the documentSources of available nutrients
View the documentThe most suitable materials for bioconversion
View the documentCharacteristics of residues
View the documentBioconversion systems
View the documentPhysical and chemical treatments
View the documentMicrobial conversion
View the documentThe animal conversion phase
View the documentSummary
View the documentReferences

The animal conversion phase

In order to use SCP products successfully, a thorough nutritional and toxicological evaluation is necessary. Nutrient requirements and digestion in animals are species-specific and so is absorption of nutrients after digestion. The metabolism of nutrients and potential toxic substances is also species-specific, as is susceptibility to toxic substances.

The consequence of this specificity is that experimental data obtained in animal testing cannot be extrapolated with certainty to other animal species. The nutritional and toxicological evaluation must, therefore, be done in all animal species for which the product is destined, i.e., the target species. In guidelines for testing the nutritional and safety aspects of novel sources of protein, as formulated by the Protein Calorie Advisory Group of the United Nations System (PAG) (4, 5), this is taken into account.

Table 9 shows digestibility coefficients of a fungal product in two different monogastric species - poultry and pigs. The digestibility of the organic matter, which is close to 80 for pigs, is a mere 24 for chickens. Protein digestibility differs somewhat less dramatically. The table suggests that the difference is probably caused by the difference in digestibility of crude fibre. In the final analysis, the metabolizable energy available for chickens is only one-third of that for pigs. The difference between species is usually less marked, but the figures illustrate that specific reactions of animals must be taken into account in the evaluation of SCP.

TABLE 9. Digestibility Coefficients of a Fungal Product

  Pigs Chickens
Organic matter 79 24
Crude protein 71 59
Crude fat 34 18
Crude fibre 99 6
Metabolizable energy (kcal/kg) 2,940 1,000

When the basic nutritional and toxicological evaluations have been completed with satisfactory results, the product can be submitted for approval by government authorities.

When producing SCP products commercially, biological testing must ensure that they comply with the specifications of the product for which approval was originally obtained. If the product is modified after testing, the initial experimental data may no longer be applicable.

The final stage of testing should include optimum application of the product in the rations for the animal species that will consume these rations in the countries where the product will be applied. Here, too, specific environmental and social factors may play a major role. Table 10 presents the kinds and numbers of animals available for conversion of residues into protein, but the acceptability of their products differs greatly among regions and cultures.

TABLE 10. Number of Domestic Animals in World /in millions)

  World Africa Latin America South Asia S.E. Asia Near East
Cattle 1,214 160 266 199 23 46
Buffaloes 132 2 - 73 14 4
Sheep 1,038 159 120 77 3 137
Goats 413 127 41 87 9 62
Pigs 645 8 72 7 25 -
Chickens 6,116 488 721 192 307 236