The effect of forage theoretical cut lengths on chewing activity, rumen fermentation, dissolved gases, and methane emissions in goats

Abstract

Rumen gases include hydrogen (H2), methane (CH4) and carbon oxide (CO2), which are mainly produced during the carbohydrate fermentation to volatile fatty acids. Forage particle size alters chewing activities, which can influence reticulo-rumen motility, and thus may affect the rumen dissolved gases and gases emissions. We hypothesised that increasing forage theoretical cut lengths (TCL) from 20 to 100 mm would alter the distribution of forage particle sizes, which could affect chewing activity, gases production, saturation and emissions in goats. Ten Xiangdong black goats of average body weight of 37 ± 5 kg were randomly assigned to two treatments in a cross-over design. The two dietary treatments had the same concentrate diet with a difference coming from the TCL of forages (20 and 100 mm). Although forage with 100-mm forage TCL had larger particle sizes than 20-mm forage TCL, both treatments had similar physically effective fibre contents larger than 8.98 mm (peNDF>8.98mm). Increasing forage TCL did not alter (P > 0.05) feed intake, total-tract nutrient digestibility, rumen pH, VFA concentration and molar percentage of individual VFA. Increasing forage TCL greatly increased (P < 0.05) time spent for eating (+20 %), rumination (+16 %) and chewing (+17 %), but did not alter (P > 0.05) dissolved H2, CH4 and CO2 in the liquid phase of rumen, gaseous H2 and CH4 in the gas phase of rumen and enteric CH4 and CO2 emissions. Increasing forage TCL had a tendency (P = 0.08) to decrease the saturation factor of H2. In summary, although increasing forage TCL from 20 to 100 mm increased dietary forage particle size, which altered chewing activity with increased eating and rumination activities, such changes in chewing activity had little impact on rumen gases concentrations, saturation factor of gases and enteric gas emissions in goats.