Developing grass-based veal production from male dairy calves could be a low-input solution for raising such animals, particularly in organic systems. However, the impact of grazing on enteric methane emissions of young animals is not well assessed, yet. The study included three genotypes – Brown Swiss, Limousin × Brown Swiss, and Swiss Fleckvieh – raised in four distinct farming systems: a hay-based indoor system and three pasture-based systems, representing intensive, permanent, and alpine grasslands. While all grazing calves received comparable amounts of maize and alfalfa pellets, and a limited soy-free concentrate, the indoor control group followed a slightly different feeding regimen. Hay was provided ad libitum in all systems. Each genotype × system interaction comprised four male calves, raised together from day of life 90 to 180 in the respective systems. Rumen fluid was sampled by intubation after 11 weeks. In vitro gas production (ml/200 mg DM), absolute methane emissions (mg), and methane yield (mg/ml) were analysed after 24h of incubation at 38°C in a batch system. The time between sampling of the rumen fluid and start of the test run in vitro was different due to physical distances between sites and laboratory. It was included as a correction variable in the model. Analysis revealed a significant impact of the farming system on methanogenesis, whereas genotype effects were marginal and never significant. Total gas production volume was highest in the intensive grassland system and lowest in the alpine system (46.2 ml and 44.6 ml, respectively). Methane production was lowest in the indoor and intensive grassland systems, whereas the permanent and alpine grassland systems produced the highest levels—showing increases of 16% and 8%, respectively, in methane production (mg) compared to the indoor system. These results show relative differences between systems and genotypes. Scaling to emission values per unit of product is not possible, though. Further research on dietary strategies, economic feasibility, and land use efficiency is necessary to assess the sustainability of grass-based veal production.