EFFECTS OF FEEDING DRIED GRASS PASTURE AND A GRAIN RATION DIFFERING IN RUMEN UNDEGRADABLE PROTEIN AT 2 FEEDING FREQUENCIES ON NUTRIENT DIGESTIBILITY AND MICROBIAL PROTEIN-SYNTHESIS DURING CONTINUOUS-CULTURE

Four continuous culture fermenters were used in a randomized block des ign to evaluate the effects of gain feeding frequency and rumen undegr adable protein (RUP) on nutrient utilization and microbial protein syn thesis with high quality grass. Two grain rations fed two or four time s per day were arranged in a 2x2 factorial with four replications. The grain rations contained 60% and 45% of CP as RUP, and similar total n onstructural carbohydrate (TNC) content (64% of DM). Grain was fed sep arately from freeze dried, pelleted pasture (56% of DM). Fermenters we re maintained at a liquid dilution rate of 12%/h and a solids retentio n time of 20 h. Regardless of RUP level or grain feeding frequency, tr ue DM, OM, and CP digestibilities averaged 72.1%, 73.3%, and 61.8%, re spectively with no differences due to treatments. Apparent digestibili ty of ADF, NDF, and TNC were also not affected by treatments, and aver aged 55.9%, 46.2%, and 80.9%, respectively. The production of the majo r VFA (acetic, propionic, and butyric) were not affected by treatment and averaged 56.4, 21.2 and 16.3 Mmol/ml, respectively. The interactio n of grain feeding frequency and dietary RUP content was significant f or isovalerate production. Increasing the grain feeding frequency sign ificantly increased valerate production. Ammonia N (NH3-N) concentrati on and flows were decreased with higher RUP supplementation, and by fe eding grain 4X/day (P<0.05). Non NH3-N flows were also higher with 4X/ day grain feeding. Feeding a high RUP grain reduced the CP percentage in bacteria and tended to cause a reduction in rumen pH (P>0.10). The interaction of time during the day when pH was measured and feeding fr equency was significant (P<0.001) reduced the diurnal variation in pH and when grain feeding frequency was measured to 4X/day. (C) 1998 Else vier Science B.V.