Grass leaf protein, a coproduct of cellulosic ethanol production, as a source of protein for livestock

Leaf protein (LP) produced as a coproduct of cellulosic ethanol production can be utilized by livestock. Effects of conservation method on protein extraction efficiency from orchardgrass (OG) and switchgrass (SG); effects of grass maturity, chemical and heat treatment, and conservation method on protein degradation of LP from OG; and amino acid profiles of OG and LP from OG before and after degradation were evaluated. Two maturities of OG and SG were harvested in 2008 with crude protein (CP) concentrations of 171 and 44 g/kg dry matter (DM; immature) and 131 and 24 g/kg DM (mature) for OG and SG, respectively. Grasses (fresh, stored, or wilted) were chopped, juice extracted with a screw press and adjusted to a pH of 3.3 with concentrated HCl, and treated with or without zinc and with heat (100 or 140 °C for 1 h) or without heat (21 °C; control) followed by centrifugation to harvest precipitated LP. Efficiencies of extraction were similar for fresh and stored, which were both higher than wilted grass (P < 0.01). Crude protein concentrations (g/kg DM) of LP were approximately twice that of the original grass for all chemical and heat treatment combinations. In vitro protein degradation of OG LP was evaluated using enzymes extracted from rumens of lactating dairy cows. Fresh OG LP treated with HCl + Zn 140 °C had the greatest reduction in CP degradation compared to HCl control. An interaction (P < 0.05) between maturity and zinc was observed with zinc decreasing CP degradation of immature OG LP more than mature OG LP after 4 h incubation. Interactions (P < 0.10) were also detected between maturity and temperature and between chemical and temperature after 12 h incubation. Heat decreased CP degradability with temperatures of 100 °C and 140 °C resulting in similar degradation (42.9 and 39.5 g/kg CP, respectively), which were lower than control (112.9 g/kg CP; P < 0.05) after 4 h incubation. There was an effect of conservation method on HCl + Zn 140 °C treated OG LP with similar degradability for stored (51.5 g/kg CP) and wilted (83.0 g/kg CP), which were higher than fresh (16.8 g/kg CP; P < 0.05) after 4 h incubation. The amino acid patterns of OG LP before and after degradation were similar. In summary, LP from fresh grass is most suitable because proteolysis during storage or wilting likely decreases protein recovery and increases ruminal degradation, and both zinc and heat treatments decrease degradability of OG LP within the rumen.