Methane emissions, feed intake, and total tract digestibility in lambs fed diets differing in fat content and fibre digestibility

This study determined enteric methane (CH4 ) emissions, intake, and apparent total tract digestibility of diets varying in fibre digestibility and fat content. A Latin square design with two levels of fat [2.0% and 6.0% dry matter (DM); low and high] and two levels of fibre digestibility [low fibre digestibility (LFbD) or high fibre digestibility (HFbD)] was used. Higher dry matter intake (DMI) was observed (P < 0.01) for LFbD versus HFbD diets (2.56 vs. 2.14 kg d−1, respectively), with no effect of fat. Fibre, DM, and organic matter digestibility were higher (P < 0.01) for HFbD than LFbD diets. Increasing fat did not affect intake or digestibility of DM or dietary constituents but there was a fibre digestibility × fat content interaction (P < 0.01) for fat digestibility. There was also a fat content × fibre digestibility interaction (P < 0.05) for CH4 (g kg−1 DMI, organic matter intake, neutral detergent fibre intake, and percent gross energy intake), with emissions being higher when fat was added to the HFbD than the LFbD diet. The CH4 emissions per kilogram of neutral detergent fibre (NDF) digested were higher (P < 0.01) for the HFbD than the LFbD diet. Methane emissions were increased by the HFbD diet, but inclusion of fat had a differential impact on CH4 emissions as a proportion of DMI or NDF intake in diets differing in fibre digestibility.