NorFor – the Nordic feed evaluation system - currently bases estimates of ruminal crude
protein and NDF degradation on data from the in sacco nylon bag technique. These
degradation profiles are fitted to an exponential model with an intercept as proposed by
Ørskov and McDonald (1979), where the intercept represents the soluble part of the substrate,
while the asymptote is the potentially degradable part (Åkerlind et al., 2011). The in vitro gas
production technique (IVGPT) is a method used to estimate fermentation kinetics of feeds, by
incubating the feeds in buffered rumen fluid and measuring the gas produced over time
(Theodorou et al., 1994). Cumulative gas production profiles have been related to dry matter
(DM) degradation, by assuming a potentially degradable pool equal to the amount of
substrate degraded at the end-point of the fermentation and a constant yield factor of gas to
degraded substrate (Dhanoa et al., 2000). The aim of this study was to examine whether DM
degradation estimated from mathematical models fitted to degradation profiles of
concentrates obtained through the in sacco technique correspond to estimates by the rapid
and less costly IVGPT.