Chemical treatment of straw for ruminant feeding with NaOH or urea – investigative steps via practical application under current European Union conditions

Weather extremes in parts of Europe have led to a renewed search for alternative feeds for ruminants. Cereal straw presents one source of fibre, which is hard to digest due to its lignin-carbohydrate complexes. Chemical and biological treatments have been investigated to improve digestibility. Here, the applicability of alkaline treatments for farming conditions under EU legislation and their efficacy were checked. Thus, we tested caustic soda (60, 120 g kg-1straw) and urea (15, 30, 45, 60 g kg-1straw without and with urease addition) applications both at laboratory scale and using a mixer-wagon. The nutritive value was evaluated analyzing chemical parameters including fibre components and estimating in vitro digestibility. The in vitro digestibility indicated by gas production, enzymatically soluble substrate and neutral detergent fibre digestibility (30h) was highest for the NaOH treatments, which did not differ by dose. Remoistening the straw to 600 g DM kg-1 was a precondition for the effectiveness of both treatments. Urease addition enhanced the intended ammonification when urea was applied at ≥ 30 g kg-1. An ambient temperature for urea treatment ≥ 25 °C was necessary and had to be maintained for at least 14 d post treatment. The determination of crude ash in NaOH treated feeds by the standard procedure and time overestimated the mineral fraction and had to be modified. This systematic approach provides guidance for feasible straw treatments for EU farmers. However, trials for feed acceptance and in vivo digestibility are needed to demonstrate the real effect in animals.