Measurement And Prediction Models Of Methane Emissions From Sheep

The emission of methane （CH4） from ruminants is a loss of energy and a significant contributor togreenhouse gas （GHG） emission resulting in global warming. The objectives of the present study wereto measure CH4emission from Chinese sheep and to develop prediction equations.Experiment1：Effects of different feeding levels on CH4emissions from sheepFifteen Dorper×thin-tailed Han crossbred, female lambs （36.60±0.93kg of BW） were randomlydivided into3groups with5sheep each and offered a pelleted mixture diet （concentrate:roughage=45:55） for ad libitum intake, or75or55%of the ad libitum （AL） intake, respectively. The experimentalduration consisted of a10-d adaptation period followed by a10-d period to measure CH4emissionsfrom sheep using an open-circuit respiration calorimetry system （Sable Systems International,Henderson, NV, USA）. Individual methane production was measured for24h. Body weight （BW） wasrecorded when each sheep entering and leaving the open-circuit respiration calorimetry system. TheCH4values for the groups of55%,75%and AL were29.11,46.87and55.26L/d, respectively。The CH4output, CH4energy and CH4per kg metabolisable BW （L/kg BW0.75） were increased significantly fromgroup55%to group AL（P<0.05）. CH4（L/d） was positively related to dry matter intake （DMI）, grossenergy intake （GEI） and BW linearly （P<0.01）. The relationship between CH4and DMI was CH4（L/d）=44.034DMI （kg）-6.514（R²=0.6801P=0.0005）; The relationship between CH4and GEI was CH4（L/d）=2.424GEI （MJ）-6.514（R²=0.6801P=0.0005）; The relationship between CH4and BW was CH4（L/d）=4.250BW（kg）-105.774（R²=0.6713P=0.0006）. The multiple relationship between CH4andDMI, BW was CH4（L/d）=2.813BW（kg）+29.538DMI（kg）-88.760（R²=0.9007P<0.0001）.Experiment2：Effects of different dietary composition on CH4emissions from sheepEight crossbred, non-castrated male lambs of Dorper×Thin-tailed Han sheep （50.4±1.1kg bodyweight （BW））, each fitted ruminal cannulae, were used in an incomplete8×4Latin square experiment（8diets and4periods of21d）. One of eight pelletized total mixed rations （TMR） with a neutraldetergent fiber （NDF） content of51.83,50.47,44.58,42.34,38.20,35.43,30.10and27.03, respectively,was offered randomly to each of the lambs and exchanged sequentially in four periods. Each periodconsisted of an8-d adaptation period and an8-d digestibility trial in metabolism cages during whichfeces and urine were collected, and CH4was measured by using open-circuit respirometrysimultaneous ly. The Nylon bag technique was used for the evaluation of ruminally fermentablenutrients with six different incubation times （0,6,12,24,48, and72h）. The ruminal pH andconcentrations of volatile fatty acids （VFA） were also measured. Prediction equations for CH4weredeveloped as linear and multiple regression models. The CH4values for the8diets were81.6,87.22,77.42,61.87,52.19,54.90,57.07and58.7L/kg fermentable organic matter （FOM）, respectively. TheCH4energy/digestible energy （CH4-E/DE） values were12.27,11.04,10.72,9.52,7.89,8.17,7.71and8.92%, respectively. CH4（L/kg FOM） was negatively related to organic matter intake （OMI）, gross energy intake （GEI）, crud protein intake （CPI）, digestible organic matter （DOM）, digestible energy （DE）,digestible crude protein （DCP）, digestible ether extract （DEE）, butyrate/total VFA （TVFA） andvalerate/TVFA （P<0.05）, but positively related to NDF intake （NDFI）, acid detergent fiber intake（ADFI）, digestible NDF （DNDF）, digestible ADF （DADF）, fermentable ADF （FADF）, fermentableNDF （FNDF）/FOM, FADF/FOM, and acetate/TVFA （P<0.05）. The relationship between CH4andnutrients intake was CH4（L/kg FOM）=0.182OMI（g）-0.547CPI（g）-1.177NDFI （g）+1.578ADFI（g）-3.396EEI（g）+154.950（R²=0.9992, P=0.0021）. The relationships between CH4and digestiblenutrients were CH4-E/DE（%）=92.902-3.259DE/GE（%）（R²=0.8318P=0.0016） and CH4-E/DE （%）=0.180DADF/DOM （%）+5.251（R²=0.9191P=0.0002）. The relationship between CH4and ruminalfermentable nutrients was CH4-E/DE （%）=0.112FADF/FOM （%）+6.135（R²=0.8887P=0.0005）. Therelationship between CH4and ruminal VFA was CH4（L/kg FOM）=0.825Acetate （mmol/L）+4.571Propionate （mmol/L）-7.159Butyrate （mmol/L）-20.310Valerate （mmol/L）+10.493Isovalerate （mmol/L）+9.030（R²=0.9989P=0.0028）.In conclusion, CH4increased linearly as the BW, DMI and GEI increased. CH4, CH4-E/GE andCH4-E/DE were affected by the ratios of forage to concentrate or dietary roughage content. Comparedwith other nutrients, NDF and ADF were more reliable to estimate CH4production with higherprecision. Compared with the linear regression models, the multiple regression models clearly provideda higher accuracy and correlation. Therefore, they may be useful to improve the prediction of CH₄emissions from Chinese sheep.