The effect of ammoniation on the nutritive value of wheat, barley and oat straws. II. Digestibility and energy value measurements in vivo and their prediction from laboratory measurements

Abstract

Changes in energy value and digestibility in vivo of 22 samples of wheat, barley and oat straw following ammoniation (35 kg NH 3 t −1DM) in a commercial oven were studied using sheep. A range of laboratory measurements were also examined for their relationship with digestible energy (DE) content in vivo. Straw cultivars were used from the harvest of 1983. Ammonia treatment reduced the hemicellulose content of cell walls ( P < 0.05) and this resulted in an increased content of cellulose and lignin. The mean increases in digestible organic matter in the dry matter (DOMD), coefficient of organic matter digestibility (OMD), DE and metabolisable energy (ME) contents in vivo were 97.9 g kg −1, 0.10, 1.4 MJ kg −1 DM and 1.2 MJ kg −1 DM, respectively, although these varied considerably. Oat straw was upgraded to a lesser extent than wheat or barley straw ( P < 0.05). No significant differences between barley and wheat straw were apparent and no effect of season of sowing or straw cultivar was observed. The best linear relationships between laboratory measurements and DE content in vivo were DOMD in vitro and the cellulose content of the cell walls; combined regressions for untreated and treated straws had residual standard deviations of 0.62 and 0.67 MJ kg −1 DM, respectively. The results suggest that DOMD in vitro may be a good predictor of nutritive value, in contrast to earlier reports.