Evaluation of the Relationship between Urine Purine Derivatives with Metabolizable Energy and Metabolizable Protein in Lactating Holstein Cows

The objective of this experiment was to evaluate the relationship between purine derivatives (PD) excretion in total collection or spot sampling of urine and metabolizable energy (ME) and metabolizable protein (MP) of dairy cattle. Twenty-seven dairy cows were selected to investigate the changes of PD, creatinine (C), and purine derivative/creatinine ratio (PD/C) in the urine of cows fed different diets using the total pooled urine samples collected throughout 7 days of trial period (total collection) or spot urine collection at 800-900 and 1800-1900 on the days 20 and 21. The rations were formulated with three levels of ME (127% ME/ME required, 100% ME/ME required, 75% ME/ME required) and three levels of MP (123% MP/MP required, 100% MP/MP required, 80% MP/MP required) using the CPM-Dairy 3 model. Our data demonstrated a strongly linear relationship between the concentration of PD (and PD/C) and ME and MP level of the diets using total collection or spot sampling. It was concluded that the concentration of PD and PD/C may have potential to predict the ME and MP supply in the dairy rations, and that the PD/C could be determined by spot urine sampling instead of total urine collection.