Protein value and degradation characteristics of pulp fibre fractions from screw pressed grass, clover, and lucerne

Abstract

Biorefinery of grassland plants may enable the production of feed for both ruminants and monogastrics at the same time. The pulp fibre fraction from twin-screw processed white clover, red clover, lucerne, and perennial ryegrass, is a major side-stream commonly considered of low value. However, it maintains a crude protein (CP) fraction of which a high proportion is expected to be fibre-associated. The pulp is expected to be suitable as forage for ruminants but knowledge of the feed value is limited.The objectives of this study were to assess the protein degradation in the rumen and the protein value of pulp compared to the original plant material, and to study the protein distribution among fibre fractions in order to evaluate the pulp as a source of forage for dairy cows.The ash concentration in the pulp was 51.1–72.3 g/kg DM compared to 86.3–104 g/kg DM in the original plant, while the in vitro digestible organic matter (DOM) in dry matter (DM) did not decrease significantly in pulp (532–689 g/kg DM) compared to plant (564–694 g/kg DM). Neutral detergent fibre (aNDF) concentration was higher in pulp (529–694 g/kg DM) than in original plant (342–503 g/kg DM), while the CP concentration of the aNDF from pulp (77.8–186 g/kg aNDF) did not differ from the concentration found in the plant aNDF (74.7–137 g/kg aNDF). Furthermore, the total amino acid (AA) concentration increased in pulp (825 g/kg CP) compared to original plant (768 g/kg CP), and the individual concentration of all essential AA in DM increased.The in situ rumen degradation of CP showed that the potentially degradable fraction was not different between plant (889–953 g/kg) and pulp (817–939 g/kg), although the fractional rate of degradation was lower in the pulp (0.093–0.109 h−1) than in the plant (0.113–0.192 h−1). Thus effective degradability (ED) of CP was lower in pulp (579–647 g/kg) than in plant (657–786 g/kg) increasing rumen escape protein (REP). The intestinal digestibility of REP was similar, thus a higher proportion of the pulp CP (225–256 g/kg) was digested in the intestine compared to plant CP (125–190 g/kg). The indigestible neutral detergent fibre (INDF) proportion of aNDF was not different between plant (88.1–422 g/kg aNDF) and pulp (85.3–460 g/kg aNDF).This study demonstrated that pulp from twin-screw pressing of white clover, red clover, lucerne, and perennial ryegrass has a protein concentration and value for ruminants, which is similar to the original plant material.