Start Date: Jul 26, 2007
End Date: Sep 30, 2011
Four, 8-week lactation trials will be conducted in air emission chambers located at the DFRC experimental farm in Prairie du Sac, WI. Each trial will include 16 mid-lactating dairy cows (4 early-, 8 mid-, 4 late-lactation) distributed evenly to 4 chambers (corresponding to 4 dietary treatments) in a 4x4 Latin square design. Trial 1 will be conducted during fall of 2007, followed by trial 2 during winter 2007-2008, trial 3 during spring of 2008 and trial 4 during summer of 2008. Diets for trials 1&3 will be a 2 x 2 factorial arrangement of primary forage source (alfalfa or corn silage) and the ionophore monensin (added or not). Cow rations will be formulated to include 55% forages and 45% concentrates (DM basis). Alfalfa silage (AS) and corn silage (CS) will be in either a 75:25 or 25:75 ratio, and both forage ratios will be fed with 220 mg/c/d of monensin or without monensin. Trials 2&4 will include the same dairy cow types and experimental procedures as described for Trials 1&3, except the 4 dietary treatments will include (DM basis) 85, 70, 55 or 40% forages (fixed 65:35 alfalfa silage:corn silage ratio) plus 15, 30, 45 or 60% concentrate, respectively. For each trial, diet adaptation periods of 10 d will be followed by 4 d emission measurement periods. During each day from 0700 to 0900, chambers will be cleaned, cows fed, and manure weighed, sampled, acidified and frozen. At 0900, chamber curtains walls will be lowered, sealed, and from 1000 to 1500 emission recordings will be made. After cows return from milking (1600), curtains will be lowered for night-time emission measurements. A photoacoustic multi-gas monitor (Innova Model 1412) will be used to makes continuous measurements of NH3, N2O, CO2, CH4, and VOCs concentrations in air emitted from the 4 chambers. During the last day of each trial, manure from each diet will be added to 55 gallon drums, mixed and diluted with water to mimic manure storage of a typical commercial farm. Diet manure will be stored in drums for 60 days and manure samples and gas samples collected on day 0, 3, 6, 9, 12, 18, 24, 36, 48, and 60 d after loading.