Controlled tests in farm animals may contribute useful information concerning safety or nutritional value for man. Manure as feed Systematic investigation of the use of animal waste as feed began in the 1940s. 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.
Fish can utilize non-protein nitrogen in manure added to pond water in appropriate amounts.
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. Excreta of less well-fed animals may be expected to be of lower value. Health hazards are particularly important.