A Basic Model to Predict Enteric Methane Emission from Dairy Cows and Its Application to Update Operational Models for the National Inventory in Norway

Abstract

The aim of this study was to develop a basic model to predict enteric methane emission from dairy cows and to update operational calculations for the national inventory in Norway. Development of basic models utilized information that is available only from feeding experiments. Basic models were developed using a database with 63 treatment means from 19 studies and were evaluated against an external database (n = 36, from 10 studies) along with other extant models. In total, the basic model database included 99 treatment means from 29 studies with records for enteric CH₄ production (MJ/day), dry matter intake (DMI) and dietary nutrient composition. When evaluated by low root mean square prediction errors and high concordance correlation coefficients, the developed basic models that included DMI, dietary concentrations of fatty acids and neutral detergent fiber performed slightly better in predicting CH₄ emissions than extant models. In order to propose country-specific values for the CH₄ conversion factor Y_m (% of gross energy intake partitioned into CH₄) and thus to be able to carry out the national inventory for Norway, the existing operational model was updated for the prediction of Y_m over a wide range of feeding situations. A simulated operational database containing CH₄ production (predicted by the basic model), feed intake and composition, Y_m and gross energy intake (GEI), in addition to the predictor variables energy corrected milk yield and dietary concentrate share were used to develop an operational model. Input values of Y_m were updated based on the results from the basic models. The predicted Y_m ranged from 6.22 to 6.72%. In conclusion, the prediction accuracy of CH₄ production from dairy cows was improved with the help of newly published data, which enabled an update of the operational model for calculating the national inventory of CH₄ in Norway.

Keywords: dairy cattle; dry matter intake; fatty acid; methane conversion factor; neutral detergent fiber; prediction model.

Figure 1

Observed versus predicted values of enteric CH₄ production and the residuals (observed minus predicted) for basic models used in Norway and the Model 3 developed in the present study. The graphs to the left show that the models overestimate CH₄ emissions at the lower range and underestimate emissions at the upper range. The graphs to the right show the presence of a linear bias (slope) and the presence of a mean bias (intercept).

Figure 1

Observed versus predicted values of enteric CH₄ production and the residuals (observed minus predicted) for basic models used in Norway and the Model 3 developed in the present study. The graphs to the left show that the models overestimate CH₄ emissions at the lower range and underestimate emissions at the upper range. The graphs to the right show the presence of a linear bias (slope) and the presence of a mean bias (intercept).