Effect of silage dry matter content and rapeseed meal supplementation on dairy cows 2. Rumen fermentation and digesta passage rate

The effects of direct-cut and wilted silage with or without rapeseed meal ( RSM) supplementation on rumen fermentation and digesta passage rates were s tudied in a 4x4 balanced Latin square experiment with four multiparous cows . The dry matter (DM) and crude protein (CP) degradabilities of silages wer e determined in sacco. RSM supplementation replaced 16% of the oat-barley c oncentrate mixture. The daily concentrate amount was 10 kg. Silages were gi ven ad libitum. The effective degradabilities of dry matter and protein (EP D) were higher (p<0.001) in direct-cut silage but wilted silage had higher (p<0.001) content of rapidly degradable protein. Rumen ammonia concentratio n was higher with direct-cut silage (10.16 versus 8.47 mmol/l, p<0.01), ref lecting higher CP content and EPD. Rumen pH and total volatile fatty acid ( VFA) concentration in rumen were not affected by silage type, and the diffe rences in molar proportions of rumen VFA's were small. The proportion of pr opionate tended to be higher (p<0.10) with wilted silage, whereas the propo rtion of butyrate was higher (133 versus 128 mmol/mol, p<0.01) with direct- cut silage. The retention time of the digesta particle phase in alimentary tract was shorter (p<0.05 or better) with wilted silage. Pool mean retentio n time (PMRT), which illustrates the retention time of particles in rumen, was shorter (34.0 versus 28.3 h, p<0.05) with wilted silage. Similarly, ret ention time of particles in the rumen pool of particles small enough to lea ve the rumen tended to be shorter (p<0.10) with wilted silage. RSM suppleme ntation tended to increase (p<0.10) numen ammonia concentration and decreas ed the molar proportion of rumen butyrate (132 versus 127 mmol/l, p<0.05). The retention time of particles in pool, which illustrates the rate of part icle break down in the rumen, was shorter (p<0.10) with RSM. In conclusion, the ruminal retention time of particles was shorter with wilted silage. Th is may affect silage digestibility negatively. (C) 2000 Elsevier Science B. V. All rights reserved.