Animal performance, and enteric methane, manure methane and nitrous oxide emissions from Murrah buffalo calves fed diets with different forage-to-concentrate ratios

The present study aimed to evaluate the effects of dietary forage : concentrate ratios on growth performance and enteric and faecal greenhouse-gas emissions from growing buffalo calves. Fifteen Murrah male calves (bodyweight = 233.35 +/- 30.92 kg; 8-12 months age) were randomly assigned to three dietary groups that were fed a mixture of berseem fodder, wheat straw and concentrate at the ratios of 20 : 60 : 20 (C20), 20 : 40 : 40 (C40) and 20 : 20 : 60 (C60) respectively, for 120 days. Enteric methane (CH4) production was estimated by the sulfur hexafluoride tracer technique. Faeces were stored for 12 weeks and CH4 and nitrous oxide (N2O) fluxes from stored faeces were estimated every 14 days. Dry-matter intake, feed conversion efficiency and nitrogen retention were not affected (P > 0.05) but average daily gain and urinary nitrogen loss (g/day) were higher for C60 than the C20 diet (P < 0.05). Daily enteric CH4 emission (g/day) was not affected but CH4 yield (g/kg dry-matter intake) and energy loss through CH4 as a proportion of energy intake were lower for C60 than the C20 diet (P < 0.05). Faeces composition was not affected, and large variations of greenhouse-gas emissions were observed for first 10 days of storage. Methane emissions from stored faces were 1.28 +/- 0.40, 1.94 +/- 0.34 and 3.90 +/- 0.27 mg/kg faeces per day for C20, C40 and C60 diets respectively, being higher for C60 than the C40 and C20 diets (P < 0.05). Methane-flux rate from faeces was greater for C60 than the C20 and C40 diets (0.75 vs 0.26 and 0.37 g/animal respectively; P < 0.05). Diet C60 increased N2O fluxes from stored faeces by 63% and 58% respectively, expressed in mg/kg faeces per day and mg/animal per day, compared with C20 diet (P < 0.05). Overall, dietary concentrate proportion of up to 60% in growing buffalo calf diets improved growth performance without increasing enteric CH4 emission, but CH4 and N2O production from faeces were increased. This work has provided information for gas emissions factors from open storage of faeces. More detailed studies on gaseous emissions from open lots on farms are required.