Energy metabolism with particular reference to methane production in Muzaffarnagari sheep fed rations varying in roughage to concentrate ratio

Methane production in Muzaffarnagari sheep was studied using open circuit respiration calorimetry technique. Twelve rams were divided in three treatment groups of four each and were fed at about maintenance with diets having three roughage (oat hay) to concentrate ratio (R : C), i.e. 92 : 8 (group I), 50 : 50 (group II), 30 : 70 (group III). Concentrate mixture was formulated to contain 93% crushed maize grain, 3.5% wheat bran and 3.5% groundnut cake fortified with minerals. Whereas the digestibility of dry matter, organic matter and energy was similar, the digestibility of nitrogen was significantly (p < 0.05) higher in groups II and III and of neutral detergent fiber (NDF) was significantly (p < 0.05) lower in-group III than the other groups. Nitrogen retention was improved but not beyond 50R : 50C. As a percent of gross energy intake, urinary energy losses in groups I, II and III were 3.0, 2.9 and 2.8%, and methane energy losses were 3.39, 3.34 and 2.98%, respectively. Even though, gross energy intakes (kcal/kg W0.75) were similar, methane loss (g) per 100 g digestible organic matter was significantly (p < 0.05) higher in group I (2.2) than in groups II (1.84) and III (1.54), the latter did not differ in this respect. Metabolisable energy (ME) value (Mcal/kg DM) and energy balances (kcal/kg W0.75) on rations in groups II and III were similar but on ration in group I was significantly (p < 0.05) lower than that in other groups. Efficiency of utilisation of ME for maintenance (km) of diets in groups I, II and III calculated as per ARC (1980) were 0.674, 0.688 and 0.693, respectively, and did not differ significantly. Based on the evaluation of three R : C, it was inferred that R : C ratio of 50 : 50 in diet of Muzaffarnagari sheep is optimum for economical and sustainable sheep production through reduced methane emissions.