Prediction of nitrogen excretion by beef cattle: a meta-analysis

Area of Science:

• Animal Science
• Environmental Science
• Nutrient Management

Background:

• Accurate estimation of nitrogen (N) excretion in beef cattle is vital for environmental protection and efficient nutrient management.
• Urine and fecal N excretion are key components of the nitrogen cycle in livestock systems.
• Existing models require refined predictions for N excretion based on dietary and animal factors.

Purpose of the Study:

• To develop empirical equations for predicting urine N and fecal N excretion in beef cattle.
• To determine key animal and dietary parameters influencing N excretion.
• To assess the partitioning of total N excretion between urine and feces.

Main Methods:

• A meta-analysis of 12 feeding trials (255 animals, 47 diets) was conducted.
• Correlation analysis identified parameters related to N excretion.
• Multivariate mixed modeling was used to create predictive equations for urine N, fecal N, and N partitioning.

Main Results:

• Developed equations showed 46-95% agreement with observed values for urine N and N partitioning.
• Independent dataset evaluation confirmed moderate agreement for urine N excretion prediction (r(2) = 0.34 to 0.86).
• Crude protein concentration (%CP) was a poor predictor of fecal N excretion (r(2) = 0.003 to 0.14).

Conclusions:

• Empirical equations provide a tool for predicting beef cattle N excretion characteristics.
• These equations can improve ammonia emission estimates in environmental models.
• Caution is advised when applying equations outside the range of the original data.