Rates of production of methane in the rumen and large intestine of sheep.

1. An isotope tracer method for estimating methane production in sheep is described. 2. The technique was used to estimate methane produced in both the upper and lower digestive tract and to determine the routes by which it was excreted. 3. Four Merino ewes given lucerne chaff (33 g every hour) were used. 4. Total methane production rate was 21 +/- 1-1 (SE) ml/min; production in the rumen accounted for 87 +/- 1-2% of the total production; 95 +/- 1-4% of the methane produced in the rumen was excreted by eructation. 5. Of the methane produced in the lower digestive tract, 89 +/- 2-3% was excreted through the lungs and 11% through the anus.