Pattern of carbon dioxide production and retention is similar in adult pigs when fed hourly, but not when fed a single meal

BACKGROUND: The understanding of bicarbonate kinetics and CO(2 )retention in the body is necessary to conduct amino acid tracer oxidation studies in both humans and laboratory animals. Significant metabolic activity is associated with eating which can affect bicarbonate steady state kinetics. A study was conducted to assess the impact of feeding regimen on the recovery of labelled bicarbonate and energy expenditure in adult female pigs (sows). Five catheterized sows (235 ± 5 kg) were fed semi-synthetic diets as: a single meal 2 h into the infusion after an overnight fast, or in eight hourly meals starting 2 h before the infusion. Oxygen consumption, CO(2 )production and (14)CO(2 )recovery (ie fraction not retained) were determined during primed, constant intravenous infusions of NaH(14)CO(3). RESULTS: The (14)CO(2 )recovery (%) after fasting (58.1 ± 4.8) was lower than that after single meal feeding (78.8 ± 5.9) or hourly meal feeding (81.0 ± 2.6, P = 0.03). CO(2 )production correlated with (14)CO(2 )recovery during hourly feeding (r = 0.40, P = 0.01); this relationship was not significant after single meal feeding (P = 0.30), probably due to physical activity-associated CO(2 )production. CONCLUSIONS: The correlation of CO(2 )retention factors with CO(2 )production during hourly feeding suggests that this regimen should be preferred for future amino acid kinetics studies.