350 Nutrient Movement in the Environment: Confined versus Grazing Systems

Grazing systems perform multiple ecosystem services including food production, climate regulation, nutrient cycling, and erosion control. Ruminants can also express their natural behaviors on pasture, with recent research revealing that dairy cows were more motivated to go outside for grazing than stay indoors consuming fresh TMR offered immediately after the afternoon milking. In addition, consumers often associate grazing systems with “healthier and happier cows” and are willing to pay premiums for “grass-fed” dairy products. However, milk production and nutrient utilization generally decrease in pasture-based compared with confinement systems, which may reduce farm profitability depending on milk pay prices. It should be noted that there is limited research reporting milk N efficiency (milk N/N intake) or methane emissions in confined versus grazing dairy cows using data collected from the same experiments. Therefore, our overarching objective was to build data sets to compare nutrient utilization in dairy cows under confinement or grazing management where milk N efficiency or methane emissions or both were reported in the same study. Dietary strategies to mitigate methane emissions in grazing dairy systems such as the use of high-quality forages (e.g., brassicas, perennial ryegrass), concentrate and seaweed supplementation, and forage species and management will be explored. For instance, Jersey cows grazing forage canola offered at 40% of the total DM emitted 31% less methane than those kept indoors and fed TMR (419 vs. 289 g/d, respectively) in an experiment conducted at the University of New Hampshire. Methane yield and methane intensity also decreased (P < 0.001) by 29.3% and 23.4%, respectively, in the same study. Irish researchers reported that methane production (-37%), yield (-11.5%), and intensity (-13%) decreased significantly in Holstein-Friesian cows offered perennial ryegrass herbage versus TMR. Data from whole-farm models comparing confinement and grazing systems will be presented and discussed.