Evaluation of the Nordic Dairy Cow Model Karoline in Predicting Methane Emissions

Abstract Text:

Models are widely used to predict methane (CH₄) emissions, and are used to develop mitigation options and policies. In the current study, the performance of the Nordic dairy cow model Karoline was evaluated in predicting CH₄ emissions. Karoline is a dynamic, deterministic and mechanistic simulation model describing the digestion and metabolism of nutrients, and production in a dairy cow. The model was evaluated against observed data from studies reporting CH₄ emissions from respiration chamber studies. The dataset included a total of 184 treatment means from 31 published papers. The dietary and animal characteristics used for the model evaluation represent the typical range of diets fed to dairy cattle. When analyzed with a fixed regression analysis, there was a good relationship between predicted and observed CH₄ emissions measured from respiration chamber studies (R² = 0.93) with a small root mean square error of prediction (RMSPE = 10.1 % of the observed mean). The mean bias was small but statistically significant, and there was no slope bias. Most of the error was due to random bias (96.4 %), whereas the contributions of mean and slope bias were small (3.4 and 0.2 %, respectively). By considering study as the random effect in the model (mixed model regression analysis), the fit improved to R² = 0.98 and RMSPE decreased to 6.1 % of the observed mean. The influence of some input variables such as total DM intake, dietary concentrations of CP, NDF and ether extract, and OM digestibility (OMD) on the residuals (observed – predicted) of CH₄ emissions were not significant. The residuals of both CH₄ emissions and OMD were significantly related to each other, indicating the Karoline model requires accurate estimates of digestion kinetic parameters as input variables. It is concluded that the Nordic dairy cow model Karoline is a useful tool in predicting CH₄ emissions and understanding the system behavior. The model can also be used in developing mitigation strategies for the national inventories of CH₄emissions.

Keywords: Karoline model; Methane emissions; Mechanistic model