Estimation of total methane emission from enteric fermentation of ruminant livestock in Bangladesh

Ruminant livestock is one of the key elementsfor the agriculture-based economy of Bangladesh, although these animals are often condemned as a source greenhouse gas especially methane (CH4).Total methane emission from the enteric fermentation of ruminants in Bangladesh considering Gazipur, Tangail and Mymensingh district is reflected in the output of the present study. The emission was measured using the dry matter intake (DMI) approach based on the total population of ruminants. Feed intake was recorded from onfarm observation and/or farmers records. It was observed that the ration supplied to bovines consisted of 5060% green roughage, 31-41% rice straw, and 4-10% concentrate mixture. In terms of DMI rice straw has been contributed the highest (51-65%) proportions followed by green forage (24-31%) and concentrate mixture (717%). In small ruminant ration, 90-95% feed (DMI 75-86%) was supplied from green grasses and remaining from concentrate mixtures. Although buffalo individually irrespective of sex and age emitted highest amount of methane followed crossbred and indigenous cattle, goat and sheep, the males produced a higher amount of methane than those of female in all species. Total methane emission in Gazipur, Tangail, and Mymensingh districts were 13359.15, 13250.65 and 13653.75 Kg/day and 4876.11, 4836.50 and 4983.62 „000‟Kg/year, respectively. In total 848,320 Kg/day and 309,630 “000”Kg/year methane was measured to be emitted in Bangladesh by 56.33 million ruminant livestock where 64.79% had come from indigenous cattle followed by crossbreed cattle (20.82%), Goat (8.79%), Buffalo (5.17%) and sheep (0.43%).


Introduction
Livestock is an integral part of agriculture and likely to be one of the most important instrumentsfor the economic growth and development of Bangladesh. There are about 23.27 million cattle (4.19 million crossbred and 19.08 million indigenous), 0.83 million buffaloes, 30.33 million goats and 1.90million sheep in Bangladesh which are essentially integrated with its agriculture as well as socioeconomic system (Banglapedia, 2014). The livestock sector contributes about 2.79% of total gross domestic products (GDP) which is almost 17.15% in total agricultural shares (Hoque et al., 2011;. Nevertheless, about 44% of the total human consumable animal protein comes from livestock sources. Moreover, 4.31% of the total foreign currency comes from the export oflivestock originated processed leather and leather goods (Bostami et al., 2015). Besides the use of power tillers and tractors in crop cultivation, 30 percent of the total tillage is operated by livestock. Furthermore, about 20 percent of the total human population is directly and 50 percent is partially dependent on livestock sector (DLS, 2016). Despite the contribution, livestock, particularly the ruminants are one of the important sources of methane emission on a global scale. According to Singhal et al. (2005), the enteric fermentation of livestock contributes the highest proportion (59%) of greenhouse gas (GHG) emitted from agriculture followed by rice cultivation (23%), manure management (5%), burning of agricultural crop residue (1%) and soils (12%). However, the anaerobic rumen acts as thestorehouse of feeds as well asa fermentation chamber in the ruminant stomach. Fermentation of carbohydrates generates free hydrogen, which is utilized by the methanogenic bacteria (like Methanobrevibacter ruminantium and Methanomicrobium mobile) in order to reduce carbon dioxide and emits methane (Singh and Mohini, 1999). The bacteria in the rumen and the methanogens with their symbiotic association increase the digestion and total microbial production. In general, about 8-12%loss of total dietary energy occurs due to the formation of methane (Blaxter, 1965). Methane production in ruminants depends on the quality, quantity, and digestibility of feed as well as the type of animal concerned. They are capable of utilizing lower quality forages and crop residues, especially rice straw and weeds fromcropland. These lowquality feeds incur low digestibility and significantly contribute to producinghigh quantities of methane. Various attempts have been made to estimate the methane emission from livestock in India (Mohini and Singh, 2001;Garg and Shukla, 2002;Gupta, 2003), in Australia (Kurihara et al., 1999), in New Zealand (Lassey, 2007), USA (Johnson and Johnson, 1995) and so on. Although a study on estimation of greenhouse gas emission from the livestock sector of Bangladesh was conducted (Jahan and Azad, 2013), the contribution of ruminants to the total production of methane in Bangladesh is not measured completely. Therefore, it is important to focus on the emission of methane by enteric fermentation of the ruminants in Bangladesh. It is also important for the better management of agricultural inputs. Keeping the aforesaid reality in mind the present study was attempted to estimate the total methane emission from different categories of ruminant animals (Cattle, Buffalo, Goat, and Sheep) fed on different types of feeds in Gazipur, Mymensingh,Tangail District as well as Bangladesh.

Materials and Methods
The body weight, feed intake, DMI, and methane production of different animal are solely dependent on sex, age, breed, variety, feedstuffs, feeding management, etc. The feeding management and availability of feeds vary among different areas. Dairy animals are generally fed athigher plane of nutrition than non-dairy animals. Only 70% of the total population of young animals of cattle and buffaloes (in the age group of 0.5-1.0yr) was considered for methane emission, as methane is not produced in young calves (0-3months) due to the nonfunctioning other men. Kids and lambs (0-2 months old) were also taken as non-methane producing animals. However, the total population of other categories of livestock was taken for methane estimation.

Identification and categorization of livestock species
Different types of the animal were categorized according to species; age and type of productivity are summarized in the Table 1.

Estimation of livestock population
The total number of animals in the different category was recorded from the Upazila Livestock Officer (ULO) and District Livestock Officer"s (DLO) office of the respective district. The livestock population of Bangladesh was cited from DLS official website (DLS, 2016), Banglapedia (2014) and Bangladesh Bureau of Statistics (BBS, 2013).

Estimation of live weight
Live weight of different categories of animals in the selected areas was estimated at farmer's house using Sheaffer"s formula  as Live weight (lbs) = G2×L/300, where, G= Heart girth (inch) and L= length of animals (inch). The weight in lbs was converted into kg dividing by a factor 2.22.

Estimation of dry matter intake (DMI)
Feed intake in terms of Kg DMI/head/day was estimated. Initially, the fresh feed intake (Kg) was estimated by surveying directly from farmer"s house of selected areas. The DMI will be calculated using the data according to Ranjan (1997) and Jain et al. (1996) considering the DM (%) of straw, green forage and concentrate mixture are 85, 28 and 85, respectively.

Estimation of methane emission
Methane conversion factor recorded in numerous feeding experiments, conducted in different laboratories will be taken into consideration. The average value of methane conversion factor [in g CH4/(kg DMI/100 Kg live weight)] for a particular category of the animal was utilized for the calculation of total methane emission from that category of livestock. The methane emission factors (MCF) for all calves, bull calf, bull and bullock of crossbred cattle along with both male and female buffalo of different age categories (18.4) were taken from Srivastova and Gurg (2002). For heifer calf,milking cow and dry cow of crossbred cattle the MCF (19.26) was taken from Singh (1999). The MCF for all categories of indigenous cattle (16.60) and goat (18.00) were used from ATI (2000). For sheep, the MCF (13.04) was elucidated from Haque and Bhar (2001). Using the MCF for different categories of livestock, the CH4 emission (g CH4/Day and Kg CH4/Year) was estimated.

Data analysis
The data generated from this experiment will be entered in Microsoft Excel worksheet, organized and processed for further analysis. The analysis was performed using statistical analysis system (SAS, 2010).

Livestock population in selected districts and Bangladesh
Data on the population of different categories of livestock collected from different sources were summarized in

Estimation of live weight and dry matter intake (DMI)
Estimated live weight (Kg) of different categories of animals is summarized in Table 3. The fresh feed intake and DMI are compiled in Figures 1 and 2. For estimating DMI the fresh feed intake (Kg) was measured by surveying directly from farmer"s house. Here, emphasis will be given to the availability of feed rather than the requirement of the animals, as methane is produced from the feed consumed during the course of its digestion. It was observed that green forages comprise about 50-60% of the total feed supplied to large bovines (cattle and buffalo) followed by rice straw (31-41%) and concentrate mixture (4-10%) (Figure 1). In terms of DMI, it was observed that rice straw contributedhighest amount (51-65%) followed by green forage (24-31%) and concentrate mixture (7-17%) (Figure 2). In the case of goat and sheep, it was observed that about 90-95% feed had come from green fodder and the remaining from concentrate mixture (Figure 1). In terms of DMI, green grasses contributed about 75-86% of total DMI (Figure 2). The results of some study on feed intake and DMI (Hossain et al., 2003;Baset et al., 2010) were also in accordance with our findings.

Estimation of methane emission
The total methane emission estimated from each category of male and female bovine (Cattle and Buffalo) per day is shown in Figures 3 and 4, and per year in Figure 5 and Figure 6. Estimation of methane from sheep and goat are shown in Figure 7 (daily) and Figure 8 (yearly). The total contribution of methane emission from each species was summarized in Figure 9. Comparison between male and female, it was observed that males of all ruminant species studied here at irrespective of their age produced a higher amount of methane than those of females (Figures 3,4,5,6,7 and 8). Species wise partition revealed that a buffalo contributed the highest amount (43.33%) followed by a crossbred cattle (31.26%), an indigenous cattle (22.78%), a goat (1.48%) and a sheep (1.16%) (Figure 9). In Bangladesh, only four types of livestock are responsible for the emission of CH 4 by the enteric fermentation. In the previous study, Jahan and Azad (2013) stated that the major contribution of the emission occurs from cattle which were about 322.5×10 6 g in 1983-84 and in 2008-09 was about 344×10 6 g. It is also mentioned in their study that the contribution ofagoatto CH 4 emission is about 71×10 6 g in 1983-84, 85.60 ×10 6 g in 1996 and 112×10 6 g in 2008-09. It was measured that the total emission of methane ( 09. An increasing pattern of methane emission over time was observed in their study. The total emission of our study is somewhat lower than the previous study, which is might be due to improved animal nutrition for animal farming in recent years. The species wise contribution was summarized in Figure 10. This study is based on the developed methane conversion factors, but furthermore accurate study, we should validate the study with direct estimation method like SF 6 Tracer Technique, Respiratory Chamber Techniques, Invitro Gas Production Technique and so on. However, the emission of methane gas from enteric fermentation in Bangladesh should be paid an attention formitigating. Methane is one of the major components ofgreenhouse gas like carbon dioxide (CO 2 ). The effect of CH 4 is almost 23 times higher than those of the effect of CO 2 . Therefore, the emission of about 100 kg Methane per year for each cow is equivalent to about 2'300 kg CO 2 per year (Ogino et al., 2007). According to FAO (2013), agriculture is responsible for 18% of the total greenhouse gas emission of the world. Livestock is taking a major part of emission from agriculture. Almost 30% of the total land of the world"s land surface is now engaged by livestock for farming, feed production etc. Now a day the human population in the world is increasing, the farming for supplying meat, milk and other animal products is also increasing. Hence the production of methane is increasing day by day. Therefore, we cannot disagree that livestock farming has a major impact on climate change and global warming. We have to find out the proper mitigation policy against the emission of methane from enteric fermentation. However, to validate our present study it is recommended to use some direct measurement techniques for measuring the emission of methane from enteric fermentation of livestock.