Eutrophication and poultry industry Issues, challenges and opportunities

Abstract

Eutrophication is the process of excessive growth of algae and cynobacteria due to over enrichmentof the surface waters with mineral nutrients. Eutrophication restricts water use for fisheries, recreation,industry and drinking. Phosphorus (P) is the limiting mineral for the eutropication process. Experiencefrom America, Europe and Austral ia clearly shows that improper land application of poultry litter isamong the main contributors of eutrophication process. Poultry utilizes dietary phosphorus ratherinefficiently, due mainly to high level ofphytate in their diets and, low intrinsic phytase activity both inpoultry and plant materials. Phytates increase the excretion of N and a range of other cations and,thus increases the eutrophic potential of poultry litter. Poultry industry of Sri Lanka expandeddramatically during the last few decades and it has been predicted that the growth will continue.Meanwhile, use of poultry litter as an organic fertilizer is becoming popular, particularly in up countrycropping systems. The, risk of getting water bodies eutrophicated due to the present trend ofindiscriminate land application of poultry litter in up country cropping systems is tremendous. Estimatedminimum annual P output from local poultry industry is around 751.8 metric tonnes. Decreasing the Plevel in faeces through dietary manipulations is probably the most cost-effective and practical approachto reduce the P losses to the environment. In poultry ration formulation, the requirement of P isexpressed as the non-phytate P requirement. No upper limits have been set for the total P level in thediet. This has given the liberty to the feed industry to use poorly digestible plant P sources in the diets.From environmental point of view, it is important to set maximum total P levels for poultry diets.Supplementation of poultry diets with microbial phytases can reduce the faecal P levels by about 30%and also faecal N and other cation levels. Regulatory mechanisms should be imposed to make theuse of phytase compulsory, at least when the total dietary P levels exceed a particular limit. A rangeof chemical and physical means are also available to increase the P utilization in poultry. Both farmersand the feed industry should be encouraged tq adopt those strategies. A maize variety with reduced phytate level has been successfully genetically engineered. Such genetically modified rice varietiesare very much needed because the excretion ofP is greatly increased when poultry diets contain ricebran. The dietary P levels commonly used in industry exceed the most recent NRC recommendationsby about 15%. Many recent researches have shown that the dietary P levels could further be reducedwithout the performance being affected. The poultry feed industry should respond to these newfindings rapidly and reduce the P levels in poultry diets. The dietary P requirement gradually declinesas birds grown and mature. Theoretically, it is possible to prepare a series of diets containing decreasingP levels, and the feeding of such a series of diets as birds grow can reduce the P excretion. Thispaper concludes that the excretion ofP from poultry industry could substantially be reduced throughdietary manipulations and, timely intervention of policy makers, farmers and researchers is of paramountimportance for the sustainability of inland water bodies.