Effects of Forage Type and Dietary Concentrate to Forage Ratio on Methane Emissions and Rumen Fermentation Characteristics of Dairy Cows in China

This study was conducted to evaluate the effects of dietary forage type and concentrate-to-forage ratio (CTFR) on CH4 emissions from dairy cows in China using the SF6 tracer method. Rumen fluid concentrations of NH4-N and VFA, rumen fluid pH, and daily milk yield were measured as well. The dietary regimens included: corn stalks (dry corn stalks after corn harvest) as the forage source at CTFR of 40:60 (ration A), corn silage as the forage source at CTFR of 40:60 (ration B), and corn silage as the forage source at CTFR of 60:40 (ration C). Twelve dairy cows (body weight = 525 ±12 kg, mean ±SE) were divided into three groups of four animals each, balanced in age and body weight, and randomly allocated to the dietary treatments. The study was run for 25 days, with the first 15 days used for adjustment and the subsequent 10 days used for response measurement. The dietary treatments ranked ration A > ration B > ration C for CH4emissions quantity (L d-1 head-1), rumen fluid pH, acetic acid concentration, and ratio of acetic acid and propionic acid concentration. For example, CH4 emissions (mean ±SE) for rations A, B, and C were 353 ±13.4, 283 ±7.48, and 263 ±9.04 L d-1 head-1, respectively, or 335 ±12.75, 270 ±7.12, and 250 ±8.6 L d-1 AU-1 (AU = 500 kg live weight). On the other hand, the treatments ranked ration A < ration B < ration C for concentrations of NH3-N, propionic acid, and butyric acid in the rumen fluid. This study indicates that CH4 emissions intensity from dairy cows (g kg-1 milk output) can be significantly reduced by using corn silage as a forage source and by increasing the content of concentrates in the ration. Compared with rations B and C, ration A increased CH4 emissions by 25% and 34% (p < 0.01), respectively. A full assessment of the effectiveness of such an improved feeding management, through life cycle analysis, in reducing carbon footprint would be warranted in future studies.