Digestibility of untreated and hydroxide-treated annual ryegrass straw

Digestion trials with sheep were carried out with untreated and NaOH-treated cubed annual ryegrass straw. In the first trial, NaOH treatment increased (P < .05) digestibility of all organic components. Organic matter digestibility was increased by 21% and energy by 32%. In the second trial, the untreated straw (different crop year) was more digestible than in the first trial (digestible energy was 47%, vs 43% in the first year). In both cases, digestibility of the straw was estimated by difference when it was fed with alfalfa hay and compared to alfalfa hay alone. When the straw was fed with urea and molasses and digestibility was estimated with book values for molasses, digestion coefficients for organic matter and acid detergent fiber were slightly higher and energy was slightly lower than when digestibility was determined by difference, but the values were not different (P > .05). NaOH treatment did not result in as much improvement in the second trial as in the first trial, but it did result in increased digestibility or organic matter and fiber; crude protein digestibility however, was lower (P < .05) with NaOH-treated than with untreated straw. TDN estimated from digestible energy appeared to give more appropriate values for straw (39.7, 41.3) and NaOH-treated straw (44.4, 46.3) relative to alfalfa hay (53.4) than those calculated by the standard method (48.2 and 50.8 for straw; 52.0 and 55.0 for NaOH-treated straw).