Saponins of Quillaja saponaria bark and the water extract obtained on homogenization of Yucca
schidigera plants were used during urea-ammoniation to reduce ammonia loss. In Expt 1, chaffed
wheat straw (2–5 cm length) was urea-ammoniated (50 g kg−1 urea, 400 g kg−1
moisture) for 25 days at 37°C with and without Quillaja saponins (QS) or Yucca plant homogenate, YPH (corresponding
to 1 and 2 g kg−1Yucca powder). The crude protein (CP) content of
untreated straw was 34 g kg−1. After 25 days, CP values of 90 g kg−1
(urea; no saponin), 82 and 86 g kg−1 (urea+QS at 1 and 2 g kg−1)
and 102 and 92 g kg−1 (urea+YPH at 1 and 2 g kg−1) were
obtained. The ammonia-nitrogen bound (as percentage of urea-nitrogen added) to straw after the treatment was 39 (urea; no saponin),
33 and 36 (urea+QS at 1 and 0·2 g kg−1), and 47 and 40 (urea+YPE at
1 and 2 g kg−1). As the extent of ammonia bound to straw was higher with
Yucca plant powder, especially at 1 g kg−1, Yucca plant
powder at 0·75 and 1 g kg−1 was used in Expt 2. In Expt 1, the Yucca plant extract was used after
homogenization of the Yucca plant powder, which is not feasible at farm level. Therefore, two simpler
approaches (overnight soaking of the powder in water (Yucca powder extracted, YPE) and mixing
of Yucca powder with the straw followed by urea-ammoniation (Yucca powder, YP) were used
besides homogenization. Otherwise, conditions for the urea-ammoniation treatment were similar to
those in Expt 1. The ammonia–nitrogen bound (as percentage of urea-nitrogen added) to the straw
varied from 47 to 54% in the presence of the Yucca plant powder, which was substantially higher than
that observed in its absence (38%). The ammonia-binding efficiency of Yucca plant powder to the
straw was highest at 1 g kg−1. Among the three methods tried, addition of the Yucca powder to straw
followed by treatment with urea was the easiest, and the binding efficiency was similar to that
observed when using the powder after homogenization. In both experiments, the true dry matter- and
NDF-digestibilities, calculated organic matter digestibility and metabolizable energy, as well as rate
and potential extent of gas production, were significantly higher (P<0·05) in the treated straw than
in the untreated straw. These values were affected neither by the source of the saponins nor the
manner in which the Yucca powder was applied.
The kinetics of inhibitor production resulting from hydrothermal deconstruction of wheat straw studied using a pressurised microwave reactor