Crude Protein Fractionation and Degradation Parameters of Limpograss Herbage

Abstract

Limpograss [Hemarthria altissima (Poir.) Stapf & Hubb.] has low crude protein (CP), but little is known about the plant's CP composition and degradation characteristics. Concentration of CP fractions A, B, and C were measured and the lag phase and rate and extent of CP degradation determined for herbage from two layers (upper 25% and next lower 50%) of limpograss canopies grazed at three heights (20, 40, and 60 cm) under continuous stocking. Slowly degradable (Fraction B) CP concentration in the dry matter (DM) was greater for the upper (21 g kg−1) than the lower (14 g kg−1) layer, and undegradable Fraction C concentration in total CP was greater in the lower (273 g kg−1) than in the upper (208 g kg−1) layer. Soluble Fraction A concentration was greatest for 20‐cm canopies, Fraction B concentration was greatest for the 40‐cm height CP basis. Fraction A concentrations in herbage CP were high across canopy heights (440–630 g kg−1), and Fraction B concentrations ranged from 190 to 310 g kg−1. Lag time of CP degradation ranged from 16 (20 cm) to 21 h (60 cm). Data suggest that (i) low total CP in the DM, resulting in low concentrations of Fractions A and B in the rumen, and the long lag phase for degradation of the B fraction contribute to protein deficiencies of cattle (Bos spp.) grazing limpograss and that (ii) grazing intensity affects forage N status, with highest concentration of N fractions that are available for rumen microbial utilization associated with closely (20 cm) grazed canopies.