| The primary objective of this study was to compare in situ and in vitro methods for determining rate and extent of legume forage digestion and the ruminal digestion kinetics of two novel forages. Rate and extent of digestion data from Rigidula medic (Medicago rigidula) and Austrian Winter Pea (Pisum sativum) were compared with data from alfalfa (Medicago sativa L.). Samples were subjected to in situ or in vitro for 3, 6, 9, 12, 15, 18, 24, 36, 48 and 96 h. Residues were analyzed for OM, NDF, and N. Estimates of OM digestibility were higher (P = 0.0001 to 0.007) for in situ at 3 through 48 h, and similar between techniques at 96 h (P = 0.08) for all three forage species. Ruminal NDF degradability at 3 through 48 h, was higher for in situ (P = 0.10 to 0.44), but similar at 96 h (P = 0.11) between techniques. Ruminal N digestibility was greater (P = 0.0001 to 0.02) for in situ than in vitro. Estimates of N Fractions A, B, and C did not differ (P = 0.32 to 0.94) for either technique. However, estimated N degradation rate was higher (P = 0.03) for in situ than in vitro, resulting in greater ( P = 0.0001) estimated ruminally degradable protein of the forage for the in situ compared to the in vitro technique. Austrian Winter Pea, Fractions A (P = 0.22), and B (P = 0.25) was similar to that of alfalfa, with Fraction C being less in the AWP than alfalfa (P = 0.01). Austrian Winter Pea had higher levels of degraded N at 3, 6, 9, 12, 15, and 96 h ( P = 0.008 to 0.03). Additionally, RDP is higher in AWP than alfalfa (P = 0.009), but the degradation rate between the two species was similar (P = 0.48). Fractions A (P = 0.22), and B (P = 0.25) in medic is similar to that of alfalfa, with Fraction C being less in the medic than alfalfa (P = 0.01). Medic had higher levels of degraded N at 3, 6, 9, 12, and 15 h, ( P = 0.009 to 0.03) where N degradation levels were similar at 18, 24, 36, and 48 h (P = 0.06 to 0.20), and at 96 h degraded N was higher in alfalfa (P = 0.008). Estimates of forage digestibility differed depending on the technique employed, and in situ or in vitro forage digestibility should not be used interchangeably. Like alfalfa, medic is a high quality forage that can be grazed by sheep or other ruminant animal. However, AWP harvested at early maturity may lack enough lignin to initiate rumination of the ruminant animal. |
