Grazing System Effects on Enteric Methane Emissions from Cows in Southern Iowa Pastures

and Implications Forage mass and nutritional quality were measured in the total forage monthly from May through September and in live forage in the upper half of the sward in June and August and related to body weights, body condition scores and daily methane emissions in pastures grazed at a stocking rate of 1.98 cows per hectare by continuous, rotational or strip-stocking at a limited forage allowance over 3 years. Strip stocking tended to increase total forage mass in comparison to continuous or rotational stocking from July through October, while increasing in vitro dry matter disappearance (IVDMD) and decreasing neutral detergent fiber (NDF) concentrations in the total live forage compared to continuous stocking in August through October. Strip stocking increased the live forage mass in the upper half of the sward in August, but live forage in the upper half of the sward in rotationally stocked pastures had greater IVDMD and crude protein concentrations than pastures grazed by continuous or strip-stocking and lower NDF concentrations than pastures grazed by strip-stocking in August. Cow body weights and condition scores of cows in strip-stocked pastures in mid to late season were lower than cows in continuously or rotationally stocked pastures, but daily methane emissions in June or August did not significantly differ between stocking systems. Results imply limiting intake of lower quality pasture forage has negative effects on cow body weight and condition while not affecting daily methane emissions. Introduction In order to develop and promote agricultural production systems that improve economic and environmental sustainability of farming enterprises, there is the need to understand the multiple impacts of agricultural practices on environmental quality. Because of the photosynthetic capacity of plants to convert carbon dioxide (CO 2) to plant biomass, the conversion of dead forage mass and roots to soil organic matter, and the lack of soil tillage, grasslands have a greater capacity for carbon sequestration than land used for row crop production. However, grazing management may affect the extent of soil organic matter accumulation in pastures. Furthermore, grazing