An open-circuit hood system for gaseous exchange measurements in small ruminants

The description of an open-circuit hood system to measure gaseous exchange in small ruminants is reported along with the equations and constants needed for automatic calculations on a computer. The performance of the system was evaluated by using a series of methanol combustion tests and respiration trials on sheep eating Rhodes grass (Chloris gayana) or Lucerne (Medicago sativa) chaffs. The total dead space was 82 1 including 72 1 of hood capacity which gave a lag-time for expired gas analyses of 50 s when the hood was ventilated at 100 1 min. The measured rate of oxygen consumption was 102±1.1% of the value as confirmed by the methanol combustion tests. Preliminary animal evaluation tests showed that the postprandial profiles of gaseous exchange in sheep could be readily measured by using the open-circuit hood system. Moreover, the pattern of gaseous exchange was dependent upon the type of forage being consumed by the sheep