Nitrogen excretion is a concern because of its potential impact on the environment inside and outside of he barn. The effects of reducing dietary protein content and the inclusion of dietary fermentable fiber sources on reducing urinary nitorgen excretion were additive, together resulting in a 55% reduction. Urinary nitrogen excretion could be predicted from plasma urea (PU) concentration. For low compared to high protein diest, urinary and total nitrogen were reduced 27% and 16%, respectively, while nitrogen rentention was reduced 7%. Lower total nitrogen exctretion may reduce land base needed to apply manure in a sustainable manner. Lower urinary nitrogen excretion will reduc ammonia emissions inside and outside the barn. Models to predict urinary nitrogen excretion may be useful to access nitrogen staus on farms.