Treatment of whole-crop cereals with alkali. 3. Voluntary intake and digestibility studies in sheep given immature wheat ensiled with sodium hydroxide, urea or ammonia

Abstract

Whole-crop winter wheat was harvested at the soft dough stage of grain development, when the crop contained ≈410 g dry matter (DM) kg −1. It was ensiled directly, either untreated or following the addition of one of the following: 58 kg NaOH; 35 kg ammonia (anhydrous); 35 kg ammonia (aqueous); 67 kg urea per tonne DM. It was then stored for 60 days. At feed-out, the untreated control silage (pH 4.0) contained high concentrations of lactic acid, acetic acid and ethanol. The NaOH silage was also acidic (pH 5.3), with high levels of lactic, acetic and butyric acid. In contrast, the nitrogenous additives produced pungent silages of high ammonia content and pH (8.4–8.9). Ammonia treatments greatly reduced lactic acid and ethanol production. Urea gave relatively high concentrations of lactic and acetic acids and smaller quantities of butyric acid and ethanol. Visual appraisal suggested that ammonia and urea have potential for controlling mould growth in silages exposed to air. In sheep, the four treatments raised the apparent digestibility of silage energy by 114, 65, 78 and 85 kJ MJ −1 GE and the consumption of digestible energy by 130, 61, 71 and 54 kJ kg −1 LW, respectively. These effects were partly or completely nullified when supplements of concentrate were given. It was concluded that it is not appropriate to conserve wheat of this maturity and moisture content, with these chemicals at the stated rates of application, because of the occurrence of extensive primary and secondary fermentation in NaOH-treated silage and excessive ammonia concentrations with the nitrogenous additives.