Methane emission by livestock in India and mitigation strategies

India has 226.1 million cattle, 96.9 million buffaloes, 59 million sheep and 124.5 million goats, 18.5 million pigs, 0.9 million each of camels and donkeys, 0.8 million horses/ponies and small a number of yak, mithun, and mules (FAO Production Year Book, Vol. 57: 2003). These animals produce 13.46 Tg methane/year (including emissions from animal wastes). The methane emission factors (kg/head/year) for different categories of animals in India are lower than in Europe and North America. Based on the studies conducted at Indian Veterinary Research Institute, methane emission factors for cattle, buffalo, sheep and goat varied from 25.6 to 57.6, 28.9 to 52.7, 2.6 to 4.1 and 3.3 to 4.3, respectively. These variations are mainly due to differences in body weight, type of feed (high vs. low fibre) and individual behaviour (high or low methane producers) of the animals. Mitigation of methane emission is essential to protect the environment from the greenhouse effect and at the same time improve feed conversion efficiency. Strategies to mitigate methanogenesis: - Non-productive or low productive animals should be replaced with either high producing indigenous cattle/buffalo or high producing crossbred cattle. If we target to enhance the population of high producing cattle from the present figure of 23 million to 46 million within next 5 years, the excretion of wastes and methane will be increased by only 3.2% and 1.7% respectively, but the production of excreta and methane per unit of livestock productivity will be considerably reduced. - Any effort made to enhance degradability of poor quality feeds results in an improvement in nutrient availability accompanied with a decrease in methanogenesis. For example, urea ammoniation of straw may serve three purposes, firstly it enhances degradability of straw, secondly the supplemented non-protein nitrogen source stimulates microbial protein synthesis in the rumen and lastly it reduces methanogenesis. - Plant secondary metabolites (saponins, tannins, lignins, essential oils, etc.) have antimicrobial activities to protect the plants against invasion by microbes. This plant property can be exploited for control of undesirable microbes in the rumen. The initial screening experiments have indicated that the extracts of plants containing secondary metabolites are effective against methanogenesis and ciliate protozoa, and some have an adverse effect on degradability of feed in the rumen. Based on the results of in vitro screening experiments, a few plants and some mixtures of plants have been selected for inclusion in the diet of ruminants to study their effect on in vivo methane emission as estimated by open circuit respiration calorimeter. - A mixture of Allium sativum, Syzygium aromaticum, Foeniculum vulgare and Mentha piperita (oil) in the ratio of 2:1:2:1 respectively, was fed to buffaloes at the rate of 2g/kg of feed. Although each of the plants individually inhibited in vitro methanogenesis, but the level of mixture feeding might not be sufficient to have a similar effect on in vivo methane emission. - Terminalia chebula and Allium sativum both inhibited in vivo methane emission, but T. chebula was more effective than the latter. Both these plants both separately and as a mixture improved dry matter digestibility of feed by 10.6 to 11.3% in. In another experiment, a mixture of 3 plants fed to cattle calves at 2% of DM intake on alternate days inhibited methane production by 9.4% and the body weight gain was 8.7% (448 vs. 412 g/d) higher as compared to control, with no adverse effect on digestibility of different nutrients. - The results of the in vivo experiments conducted so far indicate that plants containing secondary metabolites, showing promising results in in vitro experiments, do have a potential to be used as rumen modulators for controlling methane emission in ruminants. The levels used in in vitro experiments are usually very high and may not vivo experiments. Therefore, the level of feeding of plants additives has to standardized for practical application to get inhibition in methanogenesis without any adverse effect on nutrient utilization. (author)