Growing environmental concern led to increased public and scientific attention to nitrogen transfers from animal manure and slurry. Major environmental problems arise from the excessive use of nitrogen compounds. Amongst these are (i) acidification of forests and natural ecosystems through atmospheric deposition of ammonia (NH3), (ii) eutrophication of inland waters and coastal seas mainly by organic N and nitrates, (iii) contamination of groundwater by nitrates and (iv) a contribution to the global warming problem by nitrous oxide, N2O. Tracer methods using 15N stable isotope provide and excellent tool for studying such complex transfers during the different stages of animal slurry management including storage, treatment and land spreading. In this article, we present a brief review of isotopic tracer principles and history through a general description of terms, definitions and assumptions follow by the methodologies developed in our laboratory to label the ammoniacal nitrogen fraction of pig slurry using artificial 15N enrichment. The aim of our studies is to gather information concerning nitrogen pig slurry turnover and to focus on those processes, where major progress is made using the stable isotope 15N. Recent research findings are presented.