Diet effects on methane production by goats and a comparison between measurement methodologies

SUMMARY A series of studies were carried out to measure the methane (CH 4 ) production by Japanese goats fed 19 different diets (D 1 –D 19 ) varying in nutritive composition in the open circuit respiration chamber (RC) and to compare them with CH 4 estimated by the in vitro gas production test (IVGPT). Adult Japanese goats (>2 years old) with a mean body weight of 26±5·4 kg were used in these experiments. Each diet was fed to four randomly selected goats and feeding was carried out at 1·1 maintenance (M) as per National Research Council (NRC) (1981) for goats. Average CH 4 emission by goats in the RC ranged from 0·23 to 0·39 (mean value 31 ml/g dry matter intake (DMI)); when it was expressed as a proportion of gross energy or, with methane conversion rate (MCR), it ranged from 5·0 to 8·2, with an average of 6·6. Incorporation of by-products like sweet potato vine silage (SPVS) ( P =0·016), dried pumpkin ( P =0·052) and brewers' grain in the diet suppressed ( P <0·01) methanogenesis in goats, when compared with that of standard farm diet (D 1 ). The CH 4 output measured in the RC was very close to that estimated from the gas collected after 24 h and higher after 48 h of in vitro incubation. Although composition of the diets' acid detergent fibre (ADF) had a significant effect on methane emission, methane output estimated by IVGPT was very close to that measured in the RC demonstrating that this system could be used to estimate the CH 4 production potential from diets in preparing a database and also in the planning of mitigation strategies in small ruminants to improve their performance as well as to reduce greenhouse gas emissions.