Swiss diet types for cattle: how accurately are they reflected by the Intergovernmental Panel on Climate Change default values?

Abstract

In Switzerland, a considerable part of the country is mountainous. Forage-based diets dominate, as crop production and feed import are limited. Long winter periods require large amounts of conserved feeds. This results in diet types where the current Intergovernmental Panel on Climate Change (IPCC) default values for enteric and manure-derived methane may not be fully appropriate. In 10 experiments carried out in Switzerland, methane emission data were obtained from various forage-based diet types. This included enteric (open-circuit respiratory chambers) and manure-derived methane (various techniques). In dairy cows and suckler cow–calf pairs, the methane-conversion rate (Y m, methane energy, % of gross energy intake) was 7.1% (5.9–8.0) and 8.1% (7.8–8.5), respectively (IPCC default value: 6.5%). In fattening bulls, Y m increased from 4.5% to 5.4% during fattening (default: 6.5%). In the slurry of fattening bulls and dairy cows, the methane-conversion factor (% of maximum slurry-methane emission potential realised) was 0.9% and 5.3% on average when incubated at 14 and 27°C (means of 7 and 14 weeks storage), respectively (default: 15% and 48%). Accordingly, IPCC default values overestimate enteric methane emissions of Swiss forage-based fattening bulls and underestimate those of suckler beef cow–calf pairs. For dairy cows, Y m remained within the current uncertainty range given by IPCC.