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

Puchun Niu,Michael Kreuzer,Tonje Marie Storlien,Egil Prestløkken,Bente Aspeholen Åby,Jon Kristian Sommerseth,Clementina Alvarez,Alemayehu Kidane,Helge Bonesmo,Angela Schwarm

doi:10.3390/ani11071891

Abstract

Simple SummaryMany techniques exist to quantify enteric methane (CH4) 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 CH4 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 CH4 production estimates included in the national inventory was improved.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 Ym (% 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 Ym over a wide range of feeding situations. A simulated operational database containing CH4 production (predicted by the basic model), feed intake and composition, Ym 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 Ym were updated based on the results from the basic models. The predicted Ym 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.

Highlights

The increase in global average surface temperature over the past half-century cannot be fully explained by natural climate variability
The subset for basic model development from Storlien et al [7] was extended by adding data published since 2013 where CH4 production, forage proportion, dry matter intake (DMI) and contents of EE or FAs and NDF in diets for dairy cows were reported (n = 21 treatment means from 8 studies, highlighted in grey shading in Table 1; Nordic, European and intercontinental origin)
The overall performance of the extant models using only DMI as input variable did not perform as good as models where dietary FAs and/or NDF were included as input variables in addition to DMI

Summary

Introduction

The increase in global average surface temperature over the past half-century cannot be fully explained by natural climate variability. Animal husbandry is a source of anthropogenic GHG emission with CH4 and N2 O as main gases, accounting for 30% of the total emissions by the agricultural sector [2]. Through CH4 , dairy production systems contribute, expressed in CO2 -equivalents, approximately one-half of the GHG emissions attributed to animal husbandry. Enteric CH4 arises mainly as a side-product from rumen microbial fermentation of feed, especially fiber, to volatile fatty acids (VFAs). This fermentation process generates an excess of hydrogen (H2 ) that is removed in the rumen by methanogens through reduction of CO2 to CH4

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