Validation of the doubly labeled water method in growing pigs

Impact of milk and nutrient intake of piglets and sow milk composition on piglet growth and body composition at weaning

The main objective of this study was to evaluate the impact of milk intake, milk composition, and nutrient intake on piglet growth in lactation and body composition at weaning. To evaluate the body composition of piglets, data from one experiment (44 Danish Landrace × Yorkshire × Duroc piglets) were used to develop prediction equations for body pools of fat, protein, ash, and water based on live weight and deuterium dilution space (exp. 1). Furthermore, a total of 294 piglets (Danish Landrace × Yorkshire × Duroc) from 21 sows of second parity were included in a second experiment (exp. 2). In exp. 2, piglet live weight was recorded on days 3, 10, 17, and 25 of lactation. On the same days, the milk intake and body composition were measured, using the deuterium oxide (D2O) dilution technique. Piglet weight gain was highly positively correlated with the intake of milk and the intake of milk constituents each week and on an overall basis having r values ranging from 0.65 to 0.93 (P < 0.001). When evaluating regressions for piglet growth, the milk intake in combination with the milk protein concentration explained 85% and 87% of the total variation in piglet gain in the second and third week of lactation, respectively, whereas milk intake was the only predictor of piglet gain in the first week of lactation explaining 81% of the variation. Fat, protein, and energy retention rates were all highly positively correlated with the daily intake of milk and intake of milk nutrients with r values ranging from 0.76 to 0.94 (P < 0.001). Piglet gain and retention rates were rather weakly correlated with the milk composition with r values ranging from 0.01 to 0.50 (being either negative or positive). Curvilinear response curves were fitted for live weight gain and body fat content at weaning in response to milk protein concentration, showing that live weight gain was slightly greater and body fat content was slightly lower at 4.9% milk protein, but it should be emphasized that the quadratic effects did not reach significance. Body fat content at weaning was positively related with the intake of milk (R2 = 0.44, P < 0.001) and milk fat (R2 = 0.46, P < 0.01). In conclusion, milk intake had a major impact on the piglet growth rate, and milk fat intake greatly influenced the body fat percentage at weaning, whereas milk composition per se only played a minor role for these traits.

Validity of the doubly labeled water method for estimating CO2 production in mice under different nutritional conditions

The doubly labeled water (DLW) technique is used to assess metabolic rate (MR) in free-living conditions. We investigated whether differences in the nutritional and body adiposity status affect validity of the assessment of CO2 production (rCO2) by the DLW technique. To serve this purpose, we compared calculated rCO2 by the DLW method to actual CO2 production concomitantly measured in an indirect calorimetry setup over a 3-day period in mice fed with a low-fat (LF) diet or an obesogenic high-fat/high-sucrose (HF) diet. To uncover a potential effect of body composition on DLW accuracy, the HF-fed group was further subdivided in a diet-induced obesity-prone (DIO) and diet-induced obesity-resistant (DR) group. Furthermore, we assessed the influence of different sampling protocols, duration, and methodology of calculation. An excellent match was found between rCO2 assessed by the two methods in the LF-fed mice (least discrepancy -0.5 ± 1.1%). In contrast, there was a consistent overestimation of rCO2 by the DLW technique in the HF-fed animals compared with actual CO2 production independent from body mass gain (least discrepancy DR +15.9 ± 2.2%, DIO +18.5 ± 3.2%). The least discrepancies were found when two-pool model equations and the intercept method were used to calculate the body water pool. Furthermore, the HF group presented different equilibration kinetics of (2)H and (18)O and a lower dilution space ratio between the two. We recommend particular caution when using the DLW method for MR assessment in HF-fed animals and potentially humans because of the overestimation of rCO2.

Validation of the doubly labeled water method in rats during isolation and simulated weightlessness

Total energy expenditure (TEE) of rats during simulated microgravity is unknown. The doubly labeled water method (DLW) reliably measures TEE, but the results depend on the methods of calculation. These methods were validated and appraised by indirect calorimetry in eight rats during isolation (7 days) and simulated microgravity (10 days). There were no effects on CO(2) production in the method used to derive constant flux rates as in the regression models. r(CO(2)) estimates were dependent on the assumed fractionation processes, the derivation of constant flux rate methods, and the selected pool models. Use of respiratory or food quotients did not influence TEE estimations, which were similar during isolation and simulation. During either isolation with growth or simulation with a stabilized mass, the one-pool model of Speakman (Speakman JR. Doubly Labelled Water. Theory and Practice. London: Chapman and Hall, 1997) resulted in the more reliable validation (0.8 +/- 2.2 and 2.2 +/- 3.4% vs. calorimetry, respectively). However, during simulation, agreement was also observed with the single pool model of Lifson (Lifson N, Gordon GB, and McClintock R. J Appl Physiol 7: 704-710, 1955) (-2.5 +/- 2.5%), and two two-pool models [Schoeller (Schoeller DA. J Nutr 118: 1278-1289, 1988) (0.5 +/- 3.1%) and Speakman (Speakman, JR. Doubly Labelled Water. Theory and Practice. London: Chapman and Hall, 1997) (-1.9 +/- 2.7%)]. This latter finding seems linked to the stable body mass and to fractionation consideration close to the single-pool model of Speakman. During isolation or simulated microgravity, the other equations underestimated TEE by 10-20%.