In vitro rumen methane output of perennial ryegrass samples prepared by freeze drying or thermal drying (40 °C)

In many in vitro studies feeds are dried in heated ovens with forced air ventilation and milled through a screen with 1 mm apertures to obtain a physically representative small sample. Drying methods involving heat have been shown to change the chemical composition of feeds, and it is possible that changes in the chemical composition during thermal drying could affect in vitro rumen CH4 output measured on the samples. Hence, samples are often dried by freeze drying. The objective of this study was to compare effects of freeze drying at −55 °C for 72 h versus thermal drying at 40 °C for 48 h on the chemical composition and CH4 output of perennial ryegrass samples collected at 5 stages of primary growth (i.e., 12 May, 26 May, 9 June, 23 June, 7 July) using an in vitro rumen gas production technique. The magnitude of the changes in chemical composition due to drying method was small and not biologically important, and drying method had no effect on CH4 output. With advancing maturity at harvest, digestibility of the herbage declined. Methane output/g dry matter (DM) incubated decreased linearly while CH4 output/g DM digested increased linearly with advancing grass maturity. Thermal drying on a range of grass samples had a similar effect to freeze drying on in vitro rumen CH4 output, reflecting the small degree of change in chemical composition. aper is part of the special issue entitled: Greenhouse Gases in Animal Agriculture – Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors: K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson.