Fractionation of fiber and crude protein in fresh forages during the spring growth

The composition of the fiber and CP of alfalfa, bromegrass, and endophyte-f ree and -infected tall fescue forages was compared during the spring growth from vegetative to reproductive stages. Forages were sampled from April 27 to June 6 in 1994, and from. April 27 to June 11 in 1995, with 11 and 12 h arvest dates, respectively. Total dietary fiber (TDF) was fractionated into insoluble and soluble fiber (SF). The CP of the forages was fractionated i nto nonprotein N (A), soluble CP (B1), insoluble CP that was soluble in neu tral detergent (B2), CP insoluble in neutral detergent but soluble in acid detergent (B3), and CP insoluble in acid detergent (C). Effects of year, fo rage species, and harvest dates (day as a covariable) were included in the model. Across harvest dates, alfalfa (A) had lower(P < .01) TDF and higher( P < .01) SF concentrations than grasses (GR) (A: 49.9 and 14.4% and GR: 60. 4 and 4.5% [OM basis] for TDF and SF, respectively). Alfalfa had higher (P < .01) CP (20.6% DM) than GR (15.3%). The rate of decrease in CP (% DM) acr oss days was higher (P < .01) for bromegrass (-.4%/d) than for the other fo rages (-.29%/d). Fraction A (% of CP) was not different (P = .24) among for ages (22.5%), but BI was higher (P < .01) in A.(17.1%) than in GR (13.2%). The B2 fraction (% of CP) was higher (P < .01) in A compared with GR (51.6 vs 45.9%, respectively). Alfalfa had lower (P < .01) B3 (3.0% of CP) than b romegrass (18.6%) and tall fescue (13.2%). Fraction C was not different (P = .23) among forages (3.8%). Fractions A, B1, and C (% of CP) did not chang e (P > .05) across days for all forages. Fraction B2 (% of CP) decreased ac ross days in A(-.21%/d) but was not affected in GR. Fraction B3 (% of CP) i ncreased (P < .05) in A (.1%/d), decreased in endophyte-infected tall fescu e( -.20%/d), and did not change (P > .05)in the other forages. Crude protei n and fiber composition were affected more by forage species than by maturi ty. The CP and NDF concentrations were more affected by maturity. Insoluble fractions but not soluble fractions of CP were affect-ed by maturity.