Methane production from dairy and beef heifers fed forages differing in nutrient density using the sulphur hexafluoride (SF6) tracer gas technique

The effects of cattle breed type [dairy (Holstein) versus beef (Charolais x Simmental)] and forage quality (high, medium and low) on methane production were measured under ad-libitum and restricted feeding conditions. The in vitro organic matter digestibility (IVOMD) of the forage diets was high = 61.5%, medium = 50.7% and low = 38.5%. Each hay diet was fed to four animals (two dairy and two beef heifers) in three periods of four 3 x 3 Latin squares. Each period consisted of 23 d during which heifers were individually fed their assigned forage for 14 d on ad-libitum feeding. Following this, intake was restricted to 2% of body weight (BW) for 9 d. Methane production was measured for five 24-h intervals in each period at both levels of intake using the, SF6 gas technique. Methane production was not different (P > 0.05) between dairy (238.0 +/- 6.9 L d(-1)) and beef cattle (228.6 +/- 7.8 L d(-1)) under either level of feeding. Forage quality affected CH4 (L d(-1)) output, with high = medium > low during ad-libitum feeding. This effect of forage quality on CH4 production was absent during restricted feeding (P > 0.05). Day-to-day variation in CH4 production was 26.9 and 27.1% on ad-libitum and restricted feeding respectively (P < 0.05), whereas animal-to-animal variation (P < 0.05) was 26.6% (ad libitum) and 25.3% (restricted). On ad-libitum feeding, dry matter intake (DMI) was strongly correlated (P = 0.0001; r = 0.8) with CH4 production (L d(-1)), and accounted for 64% of daily variation -in CH4 production. Methane [L kg(-1) digestible organic matter intake (DOMI)] was highest (P < 0.05) on low-quality diets under both feeding regimes, and was not influenced (P > 0.05) by cattle type. Methane production as a percent of gross energy intake (GEI) was not influenced by diet. It can be concluded that the SF6 tracer technique provides a measure of enteric CH4 production directly from animals under production conditions. There were no differences in CH4 production between dairy and beef breeds, but the quality of forages affected CH4 production under both ad-libitum and restricted feeding.