Effects of source and level of nitrogen, and changing buffer/ruminal fluid at 48 h on in vitro digestion of feedstuffs

The effect of source and level of N in buffer solutions, and the effect of changing buffer/ruminal fluid at 48 h of incubation on in vitro digestion of different feedstuffs at 0–96 h were investigated in three experiments using ANKOM DAISYII incubators. In Experiment 1, bags containing corn and alfalfa grass silages were introduced into the digestion jars starting with the 96 h bags and ending with the 3 h bags. Two sources of N, trypticase A containing 13.1% total N and 4.6% amino N, and trypticase B containing 13.3% total N and 6.6% amino N, were added to the buffer solutions at the recommended rate of 2.5 g/l or 1.5 times the recommended rate. Trypticase B improved (P<0.01) in vitro true DM disappearance (IVTDMD) and in vitro neutral detergent fiber disappearance (IVNDFD) of feedstuffs at 72 and 96 h, and the higher level of N decreased (P<0.05) IVTDMD and IVNDFD at 72 h. In Experiment 2, which was conducted similarly to Experiment 1 without trypticase B or the higher level of N, buffer/ruminal fluid were changed at 48 h for treatment samples, while those for control samples were not changed. Changing buffer/ruminal fluid increased IVTDMD from 82.8 to 84.0% (P<0.001) at 72 h and from 85.5 to 86.1% (P<0.05) at 96 h, increased IVNDFD from 57.9 to 61.0% (P<0.001) at 72 h and from 64.8 to 66.3% (P<0.05) at 96 h, but had no effect on the rate of IVTDMD or IVNDFD. Experiment 3 was similar to Experiment 1 except that bags for all time points were placed into the digestion jars at the beginning of the digestion run, and the respective bags removed at each endpoint of digestion. Buffer/ruminal fluid were changed at 48 h for treatment samples, while those for control samples were not changed. Changing buffer/ruminal fluid had no effect on in vitro apparent DM disappearance (IVADMD), increased IVTDMD from 76.2 to 77.8% (P<0.05) at 72 h, increased IVNDFD from 58.6 to 61.0% (P<0.001) at 72 h, but had no effect on the rate of IVADMD, IVTDMD, or IVNDFD. Even though changing buffer/ruminal fluid increased in vitro disappearances at 72 and 96 h, the magnitudes were too small to be of practical relevance.