Eutrophication and poultry industry: Issues, challenges and opportunities

Abstract

Eutrophication is the process of excessive growth of algae and cynobacteria due to over enrichment of 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. Experience from America, Europe and Australia clearly shows that improper land application of poultry litter is among the main contributors of eutrophication process. Poultry utilizes dietary phosphorus rather inefficiently, due mainly to high level of phytate in their diets and, low intrinsic phytase activity both in poultry 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 expanded dramatically 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 country cropping systems. The risk of getting water bodies eutrophicated due to the present trend of indiscriminate land application of poultry litter in up country cropping systems is tremendous. Estimated minimum annual P output from local poultry industry is around 751.8 metric tonnes. Decreasing the P level in faeces through dietary manipulations is probably the most cost-effective and practical approach to reduce the P losses to the environment. In poultry ration formulation, the requirement of P is expressed as the non-phytate P requirement. No upper limits have been set for the total P level in the diet. 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 the use of phytase compulsory, at least when the total dietary P levels exceed a particular limit. A range of chemical and physical means are also available to increase the P utilization in poultry. Both farmers and the feed industry should be encouraged to adopt those strategies. A maize variety with reducedphytate level has been successfully genetically engineered. Such genetically modified rice varieties are very much needed because the excretion of P is greatly increased when poultry diets contain rice bran. The dietary P levels commonly used in industry exceed the most recent NRC recommendations by about 15%. Many recent researches have shown that the dietary P levels could further be reduced without the performance being affected. The poultry feed industry should respond to these new findings rapidly and reduce the P levels in poultry diets. The dietary P requirement gradually declines as birds grown and mature. Theoretically, it is possible to prepare a series of diets containing decreasing P levels, and the feeding of such a series of diets as birds grow can reduce the P excretion. This paper concludes that the excretion of P from poultry industry could substantially be reduced through dietary manipulations and, timely intervention of policy makers, farmers and researchers is of paramount importance for the sustainability of inland water bodies