The urinary excretion of purine derivatives method is an effective approach for estimating microprotein output in the rumen, which is non-invasive and easy to operate. The method can accurately estimate the changes of microprotein output in the rumen. It has a lower residual variation and more consistent results. Two improvements are spot sampling method and dahlin method. The advantage of spot sampling method is the determination on appropriate sampling time, by which a high relevance between PD/C (the ratio of purine derivative to creatinine) and the daily quantity of purine derivatives can be obtained; In dahlin method, inulin, a more reliable urinary marker, is used for estimating daily creatinine excretion.［Chinese Journal of Animal Nutrition，2011，23（1）：10-14］