IN SITU RUMEN DEGRADATION KINETICS OF HIGH-PROTEIN FORAGE CROPS IN TEMPERATE CLIMATES

The present study was conducted to evaluate the nutritional value and in situ degradation kinetics of eight high protein forage crops: alfalfa ( Medicago sativa L.), forage oat ( Avena sativa L.), mixed pasture, and ryegrass ( Lolium multiflorum Lam.) pasture in early vegetative stages, two forage lupins ( Lupinus albus L.) in early bloom stages, sugar beet ( Beta vulgaris L.) and kale ( Brassica napus var. pabularia (DC.) Rchb.) leaves at root maturity. Dry matter (DM) and crude protein (CP) degradation kinetics were evaluated by the nylon bag technique through the in situ procedure described by Ørskov and MacDonald (1979) using three ruminally cannulated sheep. Chemical composition of the forage crops showed on average 13.7% DM; 21.4% CP; 31.5% neutral detergent fiber (NDF); 17.7% crude fiber (CF), 80.6% digestibility of organic matter (DOMD) and 12.13 MJ kg-1 metabolizable energy (ME). The high total degradability of forage crops reported here (> 87% DM; > 93% CP) can be associated with the presence of large quantities of fraction a (> 34% DMa; > 29% CPa) and high degradability of fraction b, resulting in low amounts of undegradable fraction (U) (7.02% DM and 3.55% CP). Correlations between CPb and DMb degradability (r = 0.79) and CPc and DMc degradation rates (r = 0.78) were high, however differences in c were not explained by differences in CP or NDF contents, nor by the amounts of a or b fractions. Degradation for DM and CP during the first 6 h of incubation was strongly and inversely correlated to b (36 h) (r = 0.93) (P < 0.0001) regardless of forage type. The amounts of CPa and CPb influenced effective degradability of CP (r = 0.79; P < 0.02), EDp increased with increased CPa and decreased with increased CPb (r = 0.76; P < 0.02). Therefore, more than 75% of the forage crops degraded within the first 6 h of incubation, which was associated with the DM content and amount of the slowly degradable fraction present.