Abstract: 【Objective】 This trial was designed to study the effects of dietary nutrients and their digestibility on rumen methane (CH4) emissions from sheep and develop regression models. 【Method】 Eight adult crossbreed rams (Dorper (♂) ×Small Tail Han sheep (♀)) with the body weight of (50.37±1.13) kg were fed 8 total mixed rations with different NDF content of 51.83%, 50.47%, 44.58%, 42.34%, 38.20%, 35.43%, 30.10% and 27.03%, respectively. The experiment design was 8×4 incomplete Latin square which lasted for 4 periods and each period lasted for 16 d. CH4 was measured by sable open-circuit respiration calorimetry system with 3 sheep once and digestive trials were conducted by total feces collection method during the last 8 d of each period. 【Result】 CH4 per kg digestive organic matter (L•kg-1 DOM) of 8 diets was 48.80, 46.98, 45.38, 41.34, 35.44, 34.66, 33.73 and 37.83, respectively. Methane regressed to NDF, ADF, nutrient intake and digestive nutrients were CH4E/DE (%)=0.14688DNDF/DOM (%)+5.47643 (R2=0.9084, P=0.0003), CH4 (L•kg-1 DOM)=0.14411DADF(g)+23.69940 (R2=0.8367, P=0.0015), CH4 (L•kg-1 DOM)=-0.22260OMI (g)+0.15234CPI (g)+0.06465NDFI (g)-0.60549EEI (g)+218.23715 (R2=0.9786, P=0.0077) and CH4 (L•kg-1 DOM)=0.09722DCP (g)+0.12079DNDF (g)-0.08355DADF (g)-1.71035DEE (g)+47.85414 (R2=0.9776, P=0.0083), respectively.【Conclusion】CH4 (L•kg-1 DOM), CH4E/GE and CH4E/DE were affected by the ratio of forage to concentrate (F﹕C) or dietary roughage content. In the linear regression models, NDF and ADF were more reliable than other nutrients to estimate methane emissions with higher precision. Compared with the linear regression models, the multiple regression models clearly provided a higher accuracy and a stronger correlation.

Key words: sheep, respiration calorimetry, methane, nutrients, regression models