Effect of sward dry matter digestibility on methane production, ruminal fermentation, and microbial populations of zero-grazed beef cattle.

Increasing the digestibility of pasture for grazing ruminants has been proposed as a low-cost practical means of reducing ruminant CH 4 emissions. At high feed intake levels, the proportion of energy lost as CH4 decreases as the digestibility of the diet increases. Therefore, improving forage digestibility may improve productivity as DM and energy intake are in- creased. A zero-grazing experiment was conducted to determine the effect of sward DM digestibility (DMD) on DMI, CH4 emissions, and indices of rumen fermen- tation of beef animals. Twelve Charolais-cross heifers were assigned to 1 of 2 treatments, with 6 heifers per dietary treatment. Additionally, 4 cannulated Aberdeen Angus-cross steers were randomly allocated to each of these 2 treatments in a crossover design. Dietary treat- ments consisted of swards managed to produce (i) high digestibility pasture (high DMD) or (ii) pasture with less digestibility (low DMD), both offered for ad libi- tum intake. All animals were zero-grazed and offered freshly cut herbage twice daily. In vitro DMD values for the high and low DMD swards were 816 and 706 g/kg of DM. Heifers offered the high DMD grass had greater (P < 0.001) daily DMI of 7.66 kg compared with 5.38