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close this bookBioconversion of Organic Residues for Rural Communities (UNU, 1979)
close this folderThe role of ruminants in the bioconversion of tropical byproducts and wastes into food and fuel
View the document(introduction...)
View the documentIntroduction
View the documentNutritional limitations in the use of tropical by-products and waste
View the documentPractical experience with tropical by-products and wastes as feed for ruminants
View the documentAn integrated system for converting tropical feeds and byproducts into milk, beef, and fuel
View the documentReferences
View the documentDiscussion summary


In many tropical countries, pressure on available land is increasing daily due to the high rate of population increase, bringing, as a consequence, increasing demands for food and the production of export crops to help the balance of payments. As a result, there is a competition for land use between traditional cattle production methods based on grazing, and arable agricultural land dedicated to the production of food crops and export crops.

In the light of these developments, it is becoming increasingly important in the tropics to integrate livestock with agriculture. One of the objectives of this paper is to show how animals, and specifically ruminants, can live and produce on the by-products and wastes of agricultural crops.

The advantages of this approach can be appreciated from a consideration of the potential benefits that can result from integration of livestock and crop production. These are:

  • the recycling of animal wastes (manure) to produce biogas by anaerobic fermentation, and later the application of the residual, partially digested slurry as organic fertilizer for crop production;
  • the saving in energy that will result from the recycling process, and the reduction in environmental contamination and health hazards;
  • the possibility of being able to exploit fully the potential of the tropics for converting solar energy into biomass by means of the production of crops of high biological efficiency with multiple uses.

The possible integration of livestock and crop production encourages decisions to be made and action initiated in the following areas. In the first place, there is the opportunity for better planning in the selection of crops for growing in the tropics, the objective being to select those with double or multiple use characteristics; in other words, crops that have a capacity to produce food for human consumption and large quantities of by-products for animal feeding. On the other hand, the decision to integrate livestock and agriculture makes it imperative to expand, rapidly and widely, research and development into systems of animal production that will encourage the more efficient utilization of these by-products and wastes from crop production and agro-industries.

As an example of crop planning, one can take the existing situation in Central America, where there is a strong tradition of growing maize as a staple for human consumption. However, on the basis of the philosophy of integrating livestock with agriculture, maize is by no means the most appropriate crop, either in its capacity to produce grain and byproducts, or in its mode of growth in the tropics, since maize is susceptible to pests and also encourages land erosion in areas of heavy rainfall. Table 1 shows the considerable advantages that would be obtained by growing bananas instead of maize, with the objective of multiple use for animal and livestock needs. It would appear that the banana plant is capable of producing more energy for human consumption (as starch) and at the same time leaves behind in the form of by-products (the forage, trunk, and leaves) very large quantities of biomass that would be capable of supporting animal stocking rates similar to, or even in excess of, those achieved normally in specialized cattle production systems based on the use of pastures.

TABLE 1. Production of Primary Product (Starch) and By-products from Maize and Banana Crops

  By-products Fresh weight


Dry weight




Digestible dry matter Primary product(starch)


Average yield 2.25 2.0 35 0.7 1.1
Excellent yield 12.0 11 0 35 3.8 5.6
Average yield 162 13 70 9 3.2
Excellent yield 430 35 70 25 9.0