Toasting of cereal grains: effects on in vitro rumen gas production and VFA yield

The fermentation properties of the following feeds: pelleted barley (PB), toasted and pelleted barley (TPB), pelleted maize (PM) and toasted and pelleted maize (TPM) were studied using an in vitro gas production (GP) technique. Each feed sample (0.5g) was incubated (3 replications), with rumen fluid collected from 3 grazing lactating dairy cows. The kinetics of GP were automatically recorded for 72h. The amounts of DM disappeared (DMd) and the volatile fatty acid yields (VFA) were measured. On barley, compared to simple pelleting, toasting significantly (P<0.05) reduced DMd (87.5 vs. 86.2%), the asymptotic GP (A, 388 vs. 367ml/g DMd) and slightly increased the time of maximum GP rate (TRmax, 2.89 vs. 3.15h). On maize toasting did not affect DMd and A, but significantly reduced T1/2 (9.71 vs. 8.57; P<0.05) and TRmax (5.04 vs. 4.49, P<0.05). Toasting significantly reduced the VFA yields both of barley and maize. These results, in agreement with previous in sacco and in vivo observations, suggest that toasting might reduce the amount of potential fermentable substrate of barley, whereas it might increase the rate of fermentation of maize.