Effects of source and level of nitrogen, and changing buffer/ruminal fluidat 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 o f different feedstuffs, at 0-96 h were investigated in three experiments us ing ANKOM DAISY(11) incubators. In Experiment 1, bags containing com and al falfa grass silages were introduced into the digestion jars starting with t he 96 h bags and ending with the 3 h bags. Two sources of N, trypticase A c ontaining 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 recomm ended rate of 2.5 g/l or 1.5 times the recommended rate. Trypticase B impro ved (P<0.01) in vitro true DM disappearance (IVTDMD) and in vitro neutral d etergent 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 Experim ent 2, which was conducted similarly to Experiment I without trypticase B o r the higher level of N, buffer/ruminal fluid were changed at 48 h for trea tment samples, while those for control samples were not changed. Changing b uffer/ruminal fluid increased IVTDMD from 82.8 to 84.0% (P<0.001) at 72 h a nd 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 effe ct on the rate of IVTDMD or IVNDFD. Experiment 3 was similar to Experiment I 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 e ach endpoint of digestion. Buffer/ruminal fluid were changed at 48 h for tr eatment 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 IV NDFD 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 incre ased in vitro disappearances at 72 and 96 h. the magnitudes were too small to be of practical relevance. (C) 2001 Elsevier Science B.V. All rights res erved.