Protein Sources for Animal Feeding
Whilst crop and agro-industrial by-products (e.g. cottonseed meal) will remain the major supply of proteins for domestic livestock production these are not always available at the sites of livestock production and at times are scarce and expensive.
In the future it will be essential to produce protein sources at, or close to ruminant production sites and to ensure protection, either during manufacture or processing or by selecting or creating plants that contain proteins that are associated with secondary plant compounds which protect the protein on chewing and ingestion. If the source of protein had also an associated antiprotozoal component the protein source will be much more active in increasing the P/E ratio in ruminants when supplemented to the basal diet.
The research will require a search for potential protein sources that will fit into the prevailing agricultural system.
The likely targets are:—
certain crops grown specifically for the purpose (e.g. lupins)
legume forages (containing tannins or harvested and protected) e.g. Lotus pendiculatus
tree leaves readily harvested and protected by processing e.g. Glyricidia spp.
seeds and seed pods e.g. Prosopis spp.
aquatic plants e.g. Azolla spp.
algaes e.g. Chlorella spp.
The options are open but on the savannahs the forage legumes and tree leaves/seeds are likely targets and in the hot dry areas on acid sandy soils, lupins might be considered. In the intensive subtropical areas the production of aquatic plants/algaes in waste waters from many sources is feasible (see Pheng Siew Moi, 1990).
The attraction of trees (e.g. Acacia, Prosopis, Leucaena, Erythrina etc.) is that the useful biomass produced with only a few trees/hectares is often the same as the biomass that can be harvested by cattle from grasslands (which seldom reaches 30% of the biomass and is often closer to 10%). The drawbacks are that it is necessary to know how to manage the trees under various conditions and usually harvesting of the leaves is hard work and expensive. However, few real attempts have been made with plantation management and mechanical harvesting.
The aquatic plants/algaes can yield up to 30 tons/ha/year of wet materials with 20–50% crude protein, they are mostly grown on enriched (by sewerage or other effluent) waste waters (see Pheng Siew Moi, 1990) and are used for cleaning purposes, again the mechanics of harvesting are major constraints. There is no real knowledge of the problem of toxic waste concentration in these sources nor of the extent of protein protection or how to effect this after harvest.
The various uses of Azolla have been summarised in a recent FAO publication (Van Hove, 1989). With Azolla as a protein source the costs of harvesting, drying and processing will be the main limitation.
The biotechnology of production of local protein resources is an area worthy of much effort. The costs of production as animal feeds could be subsidised by the production of a few fine chemicals (e.g. arachidonic acid) that are produced by algae (see Pheng Siew Moi, 1990).