In vitro fermentation kinetics of fresh and dried silage

To best simulate in vivo conditions, in vitro evaluation of feedstuffs (especially in the case of fermented silages with a high content of volatile components) should be completed using substrates as similar as possible to those that are fed to the animals. In order to investigate the effect of substrate preparation (i.e., fresh versus dried) on gas profiles, a study using an in vitro gas production technique (IVGPT) was completed with 10 silages. Each sample was incubated dried (i.e., 65 degrees C for 48 h) and fresh (frozen at -20 degrees C and milled using a butcher's cutter) using rumen fluid inoculum collected prior to the morning feeding of two buffaloes fed a standard diet. Total gas production was recorded with a manual pressure transducer and fermentation was terminated at 120 h. Degraded organic matter (i.e., OM loss) and volatile fatty acids (VFA) were also determined. Gas production was higher (P<0.01) in fresh versus dried silage. However, time of accumulation of half the potential gas produced was similar (i.e., P=O.31). Gas volume at 24 h was 228 and 162 ml/g for fresh and dried, respectively, and the maximum fermentation rate (R-M) was slower in fresh versus dried silage (R-M: 0.04 1/h versus 0.046/h, P<0.01, respectively). The time taken to reach R-M (t(RM)) was less in fresh versus dried silage (tRM: 8.93 h versus 16.0 h, respectively). There were no differences in OM degradability (707 and 708 g/kg, for fresh and dried, respectively). Fresh silages tended (P=0.068) to have higher total VFA values (90.9 mmol/g) compared to dried silage (82.9 mmol/g), but pH was higher (P<0.01) for fresh versus dried (6.71 and 6.44, respectively), probably due to its higher buffering capacity. As expected, there were differences between the silages in all in vitro fermentation parameters, and there was a substrate x preparation interaction for some (e.g., gas production, OM loss). Sample preparation of fresh silage impacts in vitro fermentation characteristics. (c) 2005 Elsevier B.V. All rights reserved.