Global climate change: Enteric methane reduction strategies in livestock

Abstract

The greenhouse gas (GHG) emission from the agricultural sector is considered to be a key contributor to the climate change, accounting for about 25.5% of total global anthropogenic emission. While carbon dioxide (CO2) receives the most attention as a factor, which causes global warming, methane (CH4), nitrous oxide (N2O), and chlorofluorocarbons (CFCs), also cause significant radiative forcing. With the relative global warming potential of 25 compared with CO2, CH4 is one of the most important GHGs. This chapter reviews the prediction models, estimation methodologies, and strategies for reducing enteric CH4 emissions. Emission of CH4 in ruminants differs between developed and developing countries, depending on factors like animal species, breed, pH of rumen fluid, ratio of acetate: propionate, methanogen population, composition of diet, and amount of concentrate fed. Among ruminants, cattle contribute the most toward greenhouse effect through methane emission, followed by sheep, goat and buffalo, respectively. The estimated CH4 emission rate per cattle, buffalo, sheep, and goat in developed countries are 150.7, 137, 21.9, and 13.7 (g/animal/day) respectively. However, the estimated rates in developing countries are significantly lower, at 95.9 and 13.7 (g/animal/day) per cattle and sheep, respectively. There is a strong interest in developing new and improving existing CH4 prediction models that are effective in identifying mitigation strategies for reducing the overall CH4 emissions. A careful examination of the literature suggests that the mechanistic models are superior to empirical models in accurately predicting the CH4 emission from dairy farms. The latest development in prediction model is the integrated farm system model, which is a process-based whole farm simulation technique. Several techniques are used to quantify enteric CH4 emissions starting from whole animal chambers to sulfur hexafluoride (SF6) tracer techniques. The latest technology developed to estimate CH4 more accurately is the micrometeorological mass difference technique. Understanding this basic information about enteric methane is very vital for formulating suitable mitigation strategies to curtail methane production. There are varieties of mitigation strategies available, which can be grouped under managemental, nutritional, and advanced molecular technologies. Strategies that are cost-effective, improve productivity, with potentially limited negative effects on livestock production are likely to be adopted by producers.