Digestibility of alkali-treated wheat straw measured in vitro or in vivo using Holstein heifers
Haddad, S.G. | Grant, R.J. | Klopfenstein, T.J.
Three experiments were conducted to determine the effect of different alkali solutions on in vitro degradation and in vivo digestibility of wheat straw. In Exp. 1, ground wheat straw was treated with 15 different alkali solutions grouped as NaOH, NH40H, urea, and Ca(OH)2. The greatest (P < .05) 48-h in vitro NDF degradability was obtained with 5% NaOH and the combination of 2.5% NaOH + 2.5% Ca(OH)2. In Exp. 2, chopped wheat straw was treated with one of the following: 1) untreated; 2) 2.5% NaOH; 3) 5% NaOH; 4) 2.5% Ca(OH)2 + 2.5% NaOH; or 5) 5% Ca(OH)2. Five Holstein heifers were fed diets that contained 60% straw, 20% alfalfa hay, and 20% concentrate mix (DM basis) fed as total mixed rations in a 5 X 5 Latin square design. The greatest in vivo NDF digestibility (P < .05) was obtained with the NaOH and NaOH + Ca(OH)2 treatments. The 5% Ca(OH)2 treatment had higher fiber digestibility than the control and was equivalent to the 2.5% NaOH and 2.5% NaOH + Ca(OH)2 treatments. Rate of passage of straw was not affected by chemical treatment, whereas rate of passage of dietary alfalfa hay increased with NaOH. In Exp. 3, wheat straw ground through a 2-mm screen was treated with one of the following chemicals: 1 untreated (control); 2) 5% NaOH; 3) 5% NH40H; 4) urea supplying N equivalent to 5% NH40H; and 5) 5% Ca(OH)2 (all on DM basis). A significant interaction (P < .05) was observed between chemical and pH for lag, rate, and extent of NDF degradation in vitro, which reflected the varying magnitude by which straw treated with different alkali sources was affected at the more acidic pH. No mechanism was determined for the effect of Ca(OH)2, but it seer that Ca(OH)2 enhances fiber degradation at low pH in vitro.
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