Performance evaluation of manure nitrogen output models suitable for lactating dairy cows in China

This is a research collaboration with China. As the most populous country in the world, China’s
demand for animal-derived foods has been rising during its transition from a poor agrarian country to a prosperous industrial society. The marked increase in manure nitrogen output caused by accelerating rapid expansion of dairy production in China is a major global environmental concern. About 70% to 80% of the nitrogen consumed by dairy cows is excreted in manure (feces and urine), which can result in substantial losses of nitrogen to the atmosphere via ammonia, nitrous oxide and nitrogen oxides and to groundwater and surface waters via leaching, erosion, and runoff. These loses in turn may further degrade the quality of soil, air, water, and natural ecosystems. Global manure nutrient management contributes an estimated 5% of anthropogenic nitrous oxide emissions to the atmosphere. Due to the environmental impact of nitrogen and the need for mitigation, various empirical models have been developed to predict nitrogen excretion from cattle (we have developed one such model for Canada); however, few models have been evaluated using data from developing countries, and no comprehensive studies have been conducted for dairy production in China. Therefore, the objective of this study was to identify models suitable for use in China by evaluating the accuracy and precision of existing models for predicting manure nitrogen output in feces and urine using published data from dairy cows in modern Chinese production conditions. A total of 35 empirical models were evaluated for their ability to predict nitrogen excretion of dairy cows in China fed a wide range of diets, and best fit models were identified. By using data from dairy cows in China, we were able to identify the best prediction models of manure nitrogen, which may improve environmental stewardship of the dairy industry in China.