Measuring enteric methane from small ruminants using respiration chambers: assessing potential effects of animal behaviour on the emission results.

Introducing the animals in a flux controlled chamber during emission tests may affect animal behavior, thus compromising the up-scaling of results. The aim of this work was to establish a protocol to evaluate how these chambers may be affecting CO2 and CH4 emissions from sheep. A 1.80 m (width) x 2.80 m (length) x 2.50 m (height) respiration chamber was constructed to measure emissions from small ruminants, according to regulations on welfare of experimental animals. 4 tests were performed with pairs of dry sheep housed in the chamber for approximately 24h. The emissions of CO2 and CH4 were measured every 5 minutes and animals were continuously recorded to assess animal activity. Sheep were also equipped with a heart rate recorder. Average CH4 and CO2 emissions of the measured animals were 21.75 g/hd/day and 896 g/hd/day respectively. During the first hour in the chamber, high CO2 emissions were recorded, in accordance with a high heart rate. Values recovered to normal levels approximately one to two hours after animals were put in the chamber. Two daily peaks were observed for emissions of both gases, one after feeding the animals (about 10:00 h) and the second about 16:00 h. Peaks of CO2 production were interpreted as an indicator of higher metabolic rates and thus, higher activity. These results were related to heart rate measurements, although more research would be necessary to confirm this hypothesis. A complete assessment of recorded videos will provide further information on feeding and ruminal activity throughout the day. According to the results obtained in this work, the introduction in the chamber seems to alter the measurements of CO2 emissions. It is necessary to assess whether CH4 emissions may also be affected by behavior changes.