Estimating losses of dry matter from wetted Alfalfa–Orchardgrass mixtures using cell wall components as internal markers

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Methods previously used to measure recoveries of dry matter (DM) from forages following natural or simulated rainfall often have relied on simple gravimetric techniques, which yielded inconclusive estimates of DM recovery. Our objective was to evaluate insoluble cell-wall constituents as internal markers for estimating recoveries of DM from alfalfa (Medicago sativa L.) or alfalfa–orchardgrass (Dactylis glomerata L.) mixtures subjected to simulated rainfall. Forage mixtures consisted of 1000, 750, or 500 g kg–1 alfalfa, with the balance comprised of orchardgrass. Regardless of the forage mixture, concentrations of all cell-wall constituents increased (P  0.053) in response to wetting (0, 70, 140, 280, 420, 560, or 840 mm at 70 mm h–1) under a rainfall simulator. Following treatment, recovery of all cell-wall constituents was high ( 901 g kg–1). Generally, losses were smallest for neutral-detergent fiber (NDF) markers regardless of analysis method (with alpha-amylase, sodium sulfite, neither, or both), acid-detergent fiber (ADF), and cellulose and largest for hemicellulose and lignin. Linear regressions of recoveries of DM by internal markers on values determined gravimetrically were good (r2  0.775) when NDF was used to estimate recovery. In all these cases, neither slopes (P  0.103) nor intercepts (P  0.083) differed from one and zero, respectively. Fiber components appear to be suitable internal markers for measuring recoveries of DM following wetting, but this approach depends on complete recovery of shattered leaf particles before conducting laboratory analyses.

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