Effect of Plant Maturity and Preservation Method on In Vitro Protein Degradation of Forages

Abstract

The influence of maturity and method of conservation on protein degradation was determined for four different forage species. Alfalfa, smooth bromegrass, and reed canarygrass were harvested at three maturities, and whole plant corn was harvested at two maturities. Samples of each forage were freeze-dried or wilted and then ensiled in mini silos at two DM contents. Additional samples of all forages except corn were field-dried to hay. Ground sample was incubated for 0, 2, and 24h with crude enzyme extract from ruminal contents. Degraded protein as a percentage of total CP was determined as the amount of protein that was soluble in TCA (80g/L) after degradation. Increased maturity resulted in lower protein degradation for alfalfa, bromegrass, and canarygrass. For example, the most mature alfalfa or bromegrass, respectively, had 77 or 63% as much N that was soluble in TCA after 2h of incubation with ruminal enzyme than the least mature forage of the same species. Although protein degradation was higher for ensiled than for dried forage, silage DM content had no consistent effect. Freeze-dried material generally had less degraded protein than hay, but protein degradation of bromegrass at 24h was lower for hay than for freeze-dried samples. Protein degradation of forages was highly variable and depended on plant maturity and conservation method.