# Modelling Nitrogen Excretion in Dairy Cows: An Application to Farms in the Po Valley (Italy)

## TL;DR

This paper presents a simplified model to estimate nitrogen excretion in dairy cows, helping farms in Italy manage environmental impacts and comply with regulations.

## Contribution

A new herd-level model for estimating nitrogen excretion in dairy cows calibrated for the Po Valley region in Italy.

## Key findings

- The model uses data from lactating cows and literature-based inputs to estimate nitrogen excretion.
- Validation showed alignment with established excretion factors and the Nitrates Directive.
- The model supports farm-level nitrogen management and identification of inefficiencies.

## Abstract

Nitrogen excretion from dairy cattle is a major contributor to environmental pollution and is subject to strict regulations in many European regions. Reliable and practical tools are therefore needed to estimate nitrogen excretion under different production conditions and to support farm-level environmental management. In this study, we developed and applied a simplified herd-level model to estimate nitrogen excretion in dairy cows under the production conditions of the Po Valley (Italy). The model relies on laboratory measurements of nitrogen excretion in faeces, urine, milk, and manure for lactating cows, together with literature-based data for other animal categories. The model is conceived as a dynamic tool that can be used by dairy farms to periodically assess their environmental performance and to generate herd-specific nitrogen excretion coefficients. Repeated assessments over time allow deviations from expected reference values to be identified, thereby facilitating the detection of management or nutritional inefficiencies and the definition of targeted mitigation actions. The model can also support compliance with environmental regulations, including those related to nitrate management.

Effective nitrogen management in dairy cow diets is essential for optimising milk production and minimising environmental nitrogen emissions. This study develops a simplified model to estimate nitrogen excretion in dairy farms, distinguishing excretion by animal category (lactating cows, heifers, calves) and organic matrix (faeces, urine), with nitrogen intake as a key input. A comprehensive literature review guided the selection of equations for estimating nitrogen excretion based on dietary nitrogen content, dry matter intake and milk yield. The model was specifically calibrated for Holstein dairy herd in the Po Valley (Italy) context using data collected from ten Lombardy dairy farms over 30 months, focusing on diet composition and nitrogen excretion via faeces, urine, and milk. Validation against established the literature and the Nitrates Directive (91/676/EEC) excretion factors demonstrated the model’s alignment in estimating nitrogen excretion. Within this context, the proposed framework may support nitrogen management at farm level by providing a practical, descriptive tool to explore nitrogen flows and to identify potential areas for improving nutrient efficiency and reducing environmental impacts.