Estimation of Excretion of Nitrogen and Phosphorus with Manure from Dairy Cow Based on Ingestion of N and P with Feeds

Through monitoring of ingestion and excretion of nitrogen and phosphorus by dairy cows of an on- scale dairy farm in summer and winter, analysis was done of relationship between the ingestion and excretion and a model was established for estimation of discharge of N and P from the farm in summer and winter. Results show that in water and summer, averagely, an adult dairy cow excretes 31.14 and 13.90 kg•d^-1 of feces per day, respectively, and a lactating cow excretes 270.71 g•d^-1 N and 66.67 g•d^-1 P with feces and urine, 16.4% and 19.2% more than a dry cow does, and 150.7% and 174.0% more than a heifer does, respectively. Daily Iingestion of nitrogen and phosphorus with fodder of a dairy cow daily varies sharply from cow to cow different in physiological stage (P<0.05), displaying an order of lactating cow > drying cow > heifer. Daily Eexcretion of nitrogen and phosphorus with feces and urine from a cow daily also varies shaprply from cow to cow different in physiological stage (P<0.05). The cows excrete with feces and urine more than 50 % of the nitrogen and phosphorus ingested. Positive relationship was found of N and P ingestions with fodder with and N and P excretions with feces, urine and milk in summer and winter. A model can hence be built up by fitting with a regression equation for estimation of N and P excretions with feces and urine based on N and P ingestions with fodder. The model may provide references for feces management and pollution prevention in dairy farms.