Evaluating lifetime nitrogen use efficiency of dairy cattle: A modelling approach

Area of Science:

• Agricultural Science
• Animal Science
• Environmental Science

Background:

• Increased nitrogen (N) use efficiency in cattle farming is crucial for reducing environmental impact.
• Existing models often overlook fertility, disease, and non-lactating animals, limiting comprehensive N management strategies.

Purpose of the Study:

• To develop a herd-level simulation model (Cattle N use efficiency - CNE) that integrates fertility, disease, and non-lactating animals to assess dairy farm N use efficiency.
• To evaluate the sensitivity of the model to various farm and animal-related input values.

Main Methods:

• Developed a CNE model with six compartments: heifer growth, removal, pregnancy, cow removal, disease/fertility, and milk production.
• Calculated lifetime N loss/gain considering replacement rate and number of lactations.
• Utilized Monte Carlo simulation for sensitivity analysis on a UK dairy farm model.

Main Results:

• Estimated mean replacement cattle N use efficiency (ReplNE) at 23.7%, primarily influenced by heifer growth.
• Dietary milk N use efficiency (MNE) strongly correlated with lifetime N use efficiencies (LactNE and LNE).
• Calving interval and time to first calving significantly impacted overall LNE, indicating the importance of fertility and growth efficiency.

Conclusions:

• The developed CNE model effectively integrates diet, fertility, and health for assessing dairy cattle N use efficiency.
• While milk production dominates N output, non-dietary factors like calving interval and heifer growth are critical for optimizing lifetime N use efficiency.