In this paper, published and some unpublished information on excretion by pigs and poultry is reviewed. Well established relationships between feed and water intake and faecal and urinary output in fattening pigs have been adapted, using modern growth curves and typical commercial feeding practice, to make estimates of excretal output for a range of growing and finishing pigs and, also, breeding sows. Nitrogen (N) outputs were then estimated from typical excretal N content. For poultry, estimates were based on empirical data available from a range of production related studies and, for broilers and turkeys, a metabolic model relating litter output to liveweight, feed inputs and feed conversion. An alternative approach of estimating N excretion, via N balance calculations, was undertaken for fattening pigs and sows and for the major poultry categories, and provides some validation of the estimated standards, increasing confidence in their application. These standards are now incorporated into the guidelines already in place for Nitrate Vulnerable Zones in England and Wales and in the recently revised Water Code.