Limits to Protein in Layer Diets Relative to Mitigating Ammonia Emission

Ammonia emissions from poultry farms currently contribute to air pollution and acid rain. There are no regulations in North America regarding emissions of ammonia although regulations are being drawn up in the USA and there is concern about the impacts of animal agricultural on the environment. Low crude protein (CP) diets can be an effective contributor to strategies of ammonia mitigation. Since virtually all ammonia originates from nitrogenous compounds in feed, then any attempt at ammonia mitigation must involve scrutiny of the levels of nitrogen, protein and amino acids (AA). Reducing dietary nitrogen/CP leads to reduced nitrogen in the excreta with less potential for microbial conversion to ammonia. Using low CP diets may be an economical strategy for ammonia emissions since the concept involves no special feed additives other than replacement AAs. Although AA requirements for layer hens are well known, the minimal amount of CP required is less clearly defined. AA requirements should be independent of diet CP, assuming there is adequate nitrogen for protein synthesis. However, the birds^/ response in terms of reduced egg numbers and growth or change in egg composition, suggest that our estimates of amino acid supply are incorrect under these dietary regimes. Independent of bird age and AA supply, more problems are recorded when CP levels are <14-15%. It is timely to redefine the maintenance AA requirements of layers. Since the composition of eggs should give us direct estimates of needs for production, the only other unknown in formulating low CP diets is the efficiency of utilisation of free amino acids versus intact proteins.