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

SIMPLE SUMMARY: Many techniques exist to quantify enteric methane (CH(4)) emissions from dairy cows. Since measurement on the entire national cow populations is not possible, it is necessary to use estimates for national inventory reporting. This study aimed to develop (1) a basic equation of enteric CH(4) emissions from individual animals based on feed intake and nutrient contents of the diet, and (2) to update the operational way of calculation used in the Norwegian National Inventory Report based on milk yield and concentrate share of the diet. An international database containing recently published data was used for this updating process. By this the accuracy of the CH(4) production estimates included in the national inventory was improved. 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 CH(4) 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 CH(4) emissions than extant models. In order to propose country-specific values for the CH(4) conversion factor Y(m) (% of gross energy intake partitioned into CH(4)) 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 CH(4) 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 CH(4) 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 CH(4) in Norway.