Effect of Sodium Silicate Added to Rumen Cultures on Digestion of Siliceous Forages

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Abstract
Aqueous sodium silicate solution added to rumen cultures depressed (P<.01) in vitro organic matter digestibility (ivOMD) of siliceous forages already known to exhibit depressed ivOMD due to silica accumulated in the plant tissues. Depression in ivOMD due to added sodium silicate varied widely (from +1.1 to −31.0 ivOMD units; ȳ ± s = 12.4 ± 7.2 units) among the 41 forage samples studied. Multiple linear regression analysis (by variable-selection, stepwise process) related the depression of ivOMD due to added soluble silica, Y, to chemical composition of forages: Ŷ = −16.2 −.4(%ADF) + 1.0(%ADL) + 4.4(%EE) + 1.0(%ASH); R2 = .52; F = 9.85** (df = 4,36). Variables not significantly related to Y were %N, %CWC and % silica in plant tissues. Aging of the sodium silicate solution (0, 15 or 30 days) before usage in the treatment of cultures increased the depression of ivOMD, apparently due to polymerization of the resulting silicic acid ("soluble silica"). When this variable was included in the regression analysis, the equation accounted for an additional 11% of the variability in depression of ivOMD (R2 = .63 vs .52). The equation was: Ŷ = −15.8 − .3(%ADF) + 1.2(%ADL) + 4.1(%EE) + 1.0(%ASH) − .3(Days silicate is aged). The regression is highly significant (F = 11.96**; df = 5,35). The depression in ivOMD due to “soluble silica” resulting from added sodium silicate was not significantly related to %N, %CWC or %silica in forage substrates. The results have importance in explaining variable effects of plant “silica” (siliceous substances) on forage digestion. Copyright © 1975. American Society of Animal Science . Copyright 1975 by American Society of Animal Science.

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