The effects of cattle breed type [dairy (Holstein) versus beef (Charolais × 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 × 3 Latin squares. Each period consisted of 23 d during which heifers were individually fed their assigned forage for 14 d on ad-ibitum 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 SF 6 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 CH 4 (L d -1 ) output, with high = medium > low during ad-libitum feeding. This effect of forage quality on CH 4 production was absent during restricted feeding (P > 0.05). Day-to-day variation in CH 4 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 CH 4 production (L d -1 ), and accounted for 64% of daily variation in CH 4 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 SF 6 tracer technique provides a measure of enteric CH 4 production directly from animals under production conditions. There were no differences in CH 4 production between dairy and beef breeds, but the quality of forages affected CH 4 production under both ad-libitum and restricted feeding.
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Boadi et al. (2002) studied this question.