Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 2/26/2008
Publication Date: 6/24/2008
Citation: Coblentz, W.K., Jokela, W.E. 2008. Estimating losses of dry matter from alfalfa-orchardgrass mixtures following rainfall events. Journal of Dairy Science. 91:27.
Technical Abstract: Studies designed to assess the effects of natural or simulated rainfall events on wilting experimental hays often have been hampered by questionable and erratic estimates of DM recovery following wetting. An alternative methodology for measuring losses of DM may be to use water-insoluble, cell-wall constituents as internal markers. Our objective was to verify this approach using insoluble cell-wall constituents [neutral-detergent fiber (NDF) without additives, NDF with alpha-amylase, NDF with sodium sulfite, NDF with alpha-amylase and sodium sulfite, acid-detergent fiber (ADF), hemicellulose, cellulose, and acid-detergent lignin] as internal markers. Forages consisted of 100, 75, or 50% alfalfa (Medicago sativa L.; wet basis), with the balance comprised of orchardgrass (Dactylis glomerata L.; 0, 25, or 50%, respectively). Forage mixtures were sealed into 18 x 30-cm custom-made Dacron bags (53-um pore size), dried under forced air (50oC) to determine accurately the initial mass of DM in each bag, and then wetted under a rainfall simulator for either 1, 2, 4, 6, 8, or 12 h at a calibrated rate of 70 mm/h (70, 140, 280, 420, 560, or 840 mm, respectively). These procedures resulted in actual losses of DM ranging from 0 to 10.4%. Following treatment, recoveries of all markers were high (=90.1%), but deviations from 100% were smallest for the NDF-based markers, as well as ADF and cellulose. Linear regressions of predicted (marker-based) recoveries of DM on actual values determined gravimetrically were especially good (r2 = 0.775) when NDF-based markers were used to estimate recovery. In all cases, neither slopes (P = 0.103) nor intercepts (P = 0.083) differed from unity and zero, respectively. Among markers requiring multiple digestion steps, ADF exhibited acceptable estimates of slope (0.84) and intercept (14.5%) that did not differ from unity (P = 0.222) and zero (P = 0.231), respectively. Neutral-detergent fiber appears to be a particularly suitable internal marker for measuring recoveries of DM following wetting; however, this approach remains contingent on complete recovery of shattered leaf particles prior to conducting laboratory analysis.