DYNAMIC ASPECTS OF OXYGEN-CONSUMPTION AND CARBON-DIOXIDE PRODUCTION IN SWINE

A model is proposed that allows study of the short-term dynamics of ga s exchanges (and heat production) in large open-circuit respiration ch ambers. The model describes changes in [O-2] and [CO2] in the respirat ion chamber by a series of differential equations based on animal meta bolism and physical characteristics of gas exchange. The model structu re was similar for O-2 and CO2, although model parameters differed. A constant level of O-2 consumption (and CO2 production) was assumed for resting animals which was different for fed and fasted animals. The a daptation from a fed to a fasting state was described as a first-order process. Physical activity (standing or sitting) was recorded and was included in the model as a constant. Thermic effect of feed comprised the O-2 consumption and CO2 production related to several relatively rapidly occurring processes after ingestion of a meal (e.g. ingestion, digestion or absorption). In the model, these processes were pooled i nto a single phenomenon. Model parameters were obtained statistically by comparing model predictions (based on the numerically integrated di fferential equations) with the observed [O-2] and [CO2]. The model was evaluated by studying gas exchanges in growing pigs that were fasted for 31 h and re-fed a single meal thereafter. The model fitted the dat a well over the 47 h measurement range. Traditional methods in which h eat production is calculated suffer from noisy data when the interval between observations becomes too short. The proposed method circumvent s this by modelling the observed concentration of gases in the respira tion chamber rather than the calculated heat production.