Enteric methane production and greenhouse gases balance of diets differing in concentrate in the fattening phase of a beef production system

The purposes of this study were 1) to assess the effects of 3 high-concentrate diets on enteric CH4 production, total tract digestibility, and rumen fermentation of beef cattle, and 2) to evaluate, by life cycle assessment, the potential effects of these feeding systems on the environment. Six bulls (age of 12.4 mo and BW of 417 kg at midexperiment) of the Blond d'Aquitaine breed were assigned to 3 dietary treatments in a replicated 3 x 3 Latin square design. Diets consisted of 1) 49% natural grassland hay, 41% ground corn grain, and 10% soybean meal (hay); 2) 63% corn silage, 21% ground corn grain, and 16% soybean meal (CS); and 3) 70% ground corn grain, 16% soybean meal, and 14% wheat straw (CG). Daily CH4 emission (g/d), measured using the sulfur hexafluoride tracer technique, was similar for the hay and CS diets and was 56% greater than for the CG diet (P < 0.001). This difference between diets was maintained when CH4 output was expressed by unit of feed intake (P < 0.001) or digested feed (P < 0.001). Gross energy intake loss as CH4 averaged 6.9% for the hay and CS diets and 3.2% for the CG diet (P < 0.001). Organic matter intake and GE intake did not differ between diets. Organic matter digestibility was less for the hay diet than for the CS and CG diets (P = 0.008). Digestibility of NDF was greatest for the hay diet, intermediate for the CS diet, and least for the CG diet (P = 0.02), with ADF digestibility being similar between the hay and CS diets and greater than for the CG diet (P < 0.001). The rumen pH at 5 h postfeeding was less for animals fed the CG diet compared with those fed the other 2 diets (on average, 5.1 vs. 5.9, respectively; P < 0.001). Total CH4 emission (enteric + manure) was least for the CG diet, whereas N2O and CO2 emissions were greatest for the CG diet. Total greenhouse gas emissions were least for the CG diet when C sequestration by grasslands was not taken into account.