|Bioconversion of Organic Residues for Rural Communities (UNU, 1979)|
|Production of feed as an objective for bioconversion systems|
Systematic investigation of the use of animal waste as feed began in the 1940s. Today, manure is being used in many countries, and this use is either regulated by laws and standards, or simply tolerated in the absence of sufficient legislation (6).
In animal nutrition, manure is of interest mainly for its nitrogen, or as a source of roughage for ruminants. Dry cattle or pig manure contains 2.5 to 3 per cent nitrogen, dry poultry waste twice as much. As a rule, half of the nitrogen is non-protein nitrogen, which is well utilized by ruminants but not by monogastric animals. Flegal and Zindel, working with broiler chicks, reported that "Feed efficiency was inversely related to the level of dried poultry waste in the diet" (7). Yet, more recent research seems to indicate that, to some extent, rats can utilize the uric acid present in poultry waste (8). With respect to fish, Kerns and Roelofs reported that growth of carp is depressed by the presence of poultry waste in a pelletized diet (9). On the other hand, mullet and catfish have been reported to grow well on diets containing 25 to 30 per cent dried poultry waste (10).
Fish can utilize non-protein nitrogen in manure added to pond water in appropriate amounts. Rappaport and coworkers observed the effect of pond manuring on the yields of carp and tilapia for three years (11). In the first year, manuring had a slight negative effect on yields. During the second season, ponds fertilized with chicken manure showed a 44 per cent increase in yields of fish over a control pond, and liquid cow manure improved yields by 13 per cent.
The chemical composition, and hence the nutritional value, of animal manures depends, of course, on the diet fed to the animals. Most of the data available refer to animals fed under conditions of intensive industrial husbandry (12). Excreta of less well-fed animals may be expected to be of lower value.
Health hazards are particularly important. Recently in Israel, an outbreak of botulism among dairy cows caused damage in excess of US$2 million. The intoxication was unequivocally traced to processed poultry waste present in the feed. It is feared that the incident may have destroyed the prospects of using poultry waste as a cattle feed ingredient in Israel for quite some time.