Using milk urea nitrogen to predict nitrogen excretion and utilization efficiency in lactating dairy cows

Area of Science:

• Animal Science
• Environmental Science
• Nutritional Biochemistry

Background:

• Animal agriculture is a significant source of nonpoint nitrogen pollution.
• Reducing nitrogen excretion in production animals is essential for environmental sustainability.
• Existing methods for monitoring nitrogen balance in dairy cows can be invasive or complex.

Purpose of the Study:

• To develop and validate a mathematical model integrating milk urea nitrogen (MUN) to predict nitrogen (N) excretion, intake, and utilization efficiency in lactating dairy cows.
• To establish target MUN concentrations for optimizing nitrogen utilization and minimizing environmental impact.
• To provide a simple, noninvasive tool for monitoring nitrogen status in dairy herds.

Main Methods:

• Developed a mathematical model using data from 3 digestibility and N balance studies (10 diets, 40 cows, 70 observations).
• Validated the model using 19 independent studies (93 diets).
• Key model variables included milk urea nitrogen, milk production, milk protein, and dietary crude protein.

Main Results:

• The model accurately predicted N excretion and efficiency with minimal bias in the developmental dataset.
• Model prediction error was approximately 15% of mean predictions in the independent dataset.
• A minimum of 10 cows is recommended for reliable model predictions.
• Target MUN concentrations of 10–16 mg/dL were determined based on National Research Council recommendations.

Conclusions:

• Milk urea nitrogen is a practical and noninvasive indicator for monitoring nitrogen excretion in lactating dairy cows.
• The developed mathematical model offers a reliable tool for assessing nitrogen utilization and environmental impact.
• Implementing this model can help reduce nitrogen pollution from dairy farming operations.