The measurement of total body water in living pigs by deuterium oxide dilution and its relation to body composition

Use of bioelectrical impedance spectroscopy to provide a measure of body composition in sows

The ability to accurately estimate fat mass and fat-free mass (FFM) has the potential to improve the way in which sow body condition can be managed in a breeding herd. Bioelectrical impedance spectroscopy (BIS) has been evaluated as a practical technique for assessment of body composition in several livestock species, but similar work is lacking in sows. Bioelectrical impedance uses population-specific algorithms that require values for the apparent resistivities of body fluids and body proportion factors. This study comprised three major aims: (i) to derive apparent resistivity coefficients for extracellular water (ECW) and intracellular water (ICW) required for validation of BIS predictions of total body water (TBW) in live sows against standard reference tracer dilution methods; (ii) to develop predictions of TBW to body composition prediction algorithms, namely FFM, by developing a body geometry correction factor (Kb) and (iii) to compare the BIS predictions of FFM against existing impedance predictors and published prediction equations for use in sows, based on physical measurements of back-fat depth and BW (P2-based predictors). Whole body impedance measurements and the determination of TBW by deuterium dilution and ECW by bromide dilution were performed on 40 Large White x Landrace sows. Mean apparent resistivity coefficients of body fluids were 431.1 Ω.cm for ECW and 1827.8 Ω.cm for ICW. Using these coefficients, TBW and ECW were over-estimated by 6.5 and 3.3%, respectively, compared to measured reference values, although these differences were not statistically different (P > 0.05). Mean Kb was 1.09 ± 0.14. Fat-free mass predictions were 194.9 kg, which equates to 60.9% of total sow weight, and 183.0 kg for BIS and the deuterium dilution method, respectively. Mean differences between the predicted and measured FFM values ranged from -8.2 to 32.7%, but were not statistically different (P > 0.05). Method validation (leave-one-out procedure) revealed that mean differences between predicted and measured values were not statistically significant (P > 0.05). Of the impedance-based predictors, equivalence testing revealed that BIS displayed the lowest test bias of 11.9 kg (8.2%), although the P2-based prediction equations exhibited the lowest bias and percentage equivalence, with narrow limits of agreement. Results indicate although differences between mean predicted and measured values were not significantly different, relatively wide limits of agreement suggest BIS as an impractical option for assessing body composition in individual sows compared to the use of existing prediction equations based on BW and back fat.

Dietary Amino Acid Deficiency Reduces the Utilization of Amino Acids for Growth in Growing Pigs after a Period of Poor Health

BACKGROUND

During immune system activation, partitioning of amino acids (AAs) changes between protein gain and use by the immune system.

OBJECTIVE

We determined the effects of health status and dietary AA deficiency on nitrogen retention and AA utilization in pigs.

METHODS

Barrows (55 d of age) were obtained from good health (GH, n = 14) or poor health (PH, n = 14) status farms and allocated to a diet either adequate in essential amino acids (Adq) or 25% deficient in Met + Cys, Thr, and Trp (Def). Nitrogen balance was measured and AA irreversible loss rates (ILRs) were measured after an intravenous bolus of U-(13)C-labeled L-AAs.

RESULTS

On arrival at the experimental facilities, the PH pigs had 14% lower serum albumin and 50% greater serum haptoglobin and blood leukocyte counts than the GH pigs (P < 0.01), but the PH pigs showed signs of recovery during the trial. Total tract nitrogen digestibility was 3 percentage points lower in the PH pigs (P < 0.01). The PH-Adq pigs had compensatory body weight gain after arrival, coinciding with 7% greater nitrogen retention (P < 0.01) in the PH pigs than in the GH pigs. The PH pigs had a 24% greater ILR for Lys. Health status × diet interactions for Lys (P = 0.07), Val (P = 0.03), and Leu (P = 0.10) pool sizes and a greater urea pool size in the PH pigs (P = 0.01) support the observation that the increase in the ILR of Lys in the PH pigs was related to oxidation when feeding the Def diet, but to synthesis when feeding the Adq diet. Feeding Def diets increased monocyte counts by 30% (P < 0.01).

CONCLUSIONS

This study illustrates how the competition for AAs between protein synthesis associated with immune system activation and body protein deposition is greater when the dietary supply of Met + Cys, Thr, and Trp is limited in pigs during and after a period of poor health.

The prediction of body composition in bacon pigs from measurements of feed intake and live-weight gain

Predictions of body composition have been made in 24 baconweight pigs of widely differing fatness, using feed intake and live-weight gain data.

Measurements of feed intake and live weight were made every 7 days throughout the growing period from 25 to 90 kg. After each pig was killed at about 90 kg, one carcass side was physically dissected and the whole empty body was chemically analysed. Multiple regression equations were then computed with the dependent variables being the weights of the physically dissectible and the chemical components. The independent variables were initial live weight, energy intake above maintenance, and live-weight gain.

The residual standard deviations of the regressions as a percentage of the mean weights of the dependent variables were for body lipid, 5·6%, fat-free mass, 3·3%, dissectible fat, 6·1 % and dissectible lean, 4·9 %. The predictions seem at least as good as can be achieved by more sophisticated techniques.

Analysis of the data allowed the efficiency of utilization of energy for protein and lipid deposition to be calculated, and an estimate of the energy costs of maintenance to be made.

Estimating total body water content in suckling and lactating llamas (Lama glama) by isotope dilution

Total body water (TBW) in 17 suckling and six lactating llamas was estimated from isotope dilution at three different post natum and lactation stages using both ¹⁸O and deuterium oxide (D₂O). In total, 69 TBW measurements were undertaken. While TBW in lactating dams, expressed in kilogram, remained stable during the three measurement periods (91.8 ± 15.0 kg), the body water fraction (TBW expressed in percent of body mass) increased slightly (P = 0.042) from 62.9% to 65.8%. In contrast, TBW (kilogram) in suckling llamas increased significantly (P < 0.001) with age and decreased slightly when expressed as a percentage of body mass (P = 0.016). Relating TBW to body mass across all animals yielded a highly significant regression equation (TBW in kilogram = 2.633 + 0.623 body mass in kilogram, P < 0.001, n = 69) explaining 99.5% of the variation. The water fraction instead decreased in a curve linear fashion with increasing body mass (TBW in percent of body mass = 88.23 body mass in kilogram^−0.064, P < 0.001, R² = 0.460). The present results on TBW can serve as reference values for suckling and lactating llamas, e.g., for the evaluation of fluid losses during disease. Additionally, the established regression equations can be used to predict TBW from body mass, providing that the body masses fall inside the range of masses used to derive the equations.

The prediction of body composition in poultry by estimation in vivo of total body water with tritiated water and deuterium oxide

1. Birds (n 169) which varied in age, live weight, nutritional history, physiological state and genotype were slaughtered and analysed for total body water. Before slaughter, birds were injected with the water isotopes tritiated water (TOH) or deuterium oxide (D2O), or both, to determine TOH space or D2O space, or both, as estimates of total body water in vivo. 2. At the mean total body water of all birds determined by desiccation, of 1096.4 (SD 424.1) g, TOH space and D2O space overestimated total body water by 10.4 and 8.5% respectively. The difference between the isotopes was significant (P less than 0.05). 3. Based on recovery of isotope it was postulated that the main reason for the observed overestimation of total body water in vivo was incomplete recovery of isotope due to the vacuum sublimation technique. The mean recovery (%) of added isotope to whole blood after vacuum sublimation was 93.0 (SD 2.6) and 92.4 (SD 5.5) of the theoretical concentrations of TOH and D2O respectively. 4. Nevertheless, accurate prediction of total body water was obtained from regression equations which included live weight and isotope-dilution space. Values required logarithmic (base 10) transformation before derivation of linear and multiple linear regression equations, and the precision of prediction was determined by the residual standard deviation (RSD). 5. Total body water could be predicted with nearly equal accuracy from live weight or isotope-dilution space (RSD 0.025 and 0.020 respectively). Prediction of carcass protein was more accurate from live weight (RSD 0.033) than from TOH space (RSD 0.036), and inclusion of both variables resulted in only a marginal decrease in RSD to 0.031. 6. The prediction of carcass fat and energy was markedly improved by the inclusion of isotope-dilution space in conjunction with live weight compared with live weight alone. 7. The relations show the developmental nature of body composition of domestic fowl given diets adequate in nutrients. The prediction equations demonstrate the precision possible for studies in which estimates of body composition in poultry are required without slaughter.

Effects of the amount and quality of dietary protein on nitrogen metabolism and protein turnover of pigs

1. The interrelation between protein accretion and whole-body protein turnover were studied by varying the quantity and quality of protein given to growing pigs. 2. Diets with 150 or 290 g lysine-deficient protein/kg were given in hourly meals, with or without lysine supplementation, to female pigs (mean weight 47 kg). 3. After the animals were adapted to the diets, a constant infusion of [14C]urea was given intra-arterially for 30 h, during the last 6 h of which an infusion of [4,5-3H]leucine was also infused at a constant rate. At the same time, yeast-protein labelled with 15N was given in the diet for 50 h. 4. The rate of urea synthesis was estimated from the specific radioactivity (SR) of plasma urea. The rate of leucine flux was estimated from the SR of plasma leucine. The irrevocable breakdown of leucine was estimated from the 3H-labelling of body water. Total N flux was estimated from the 15N-labelling of urinary urea. 5. Addition of lysine to the low-protein diet significantly increased N retention, with a substantial reduction in leucine breakdown, but there was no significant change in the flux of leucine or of total N. 6. Increasing the quantity of the unsupplemented protein also increased N retention significantly, with concomitant increases in leucine breakdown and in the fluxes of leucine and of total N. 7. It is concluded that a doubling of protein accretion brought about by the improvement of dietary protein quality is not necessarily associated with an increased rate of whole-body protein turnover.

Losses in weight and body water in sows after weaning

The loss of body water of eight sows in the 7 d following weaning was determined using the deuterium oxide dilution technique. Four of the sows had received a concentrate diet in restricted amounts while the other four had been given the same diet mixed with two-thirds its weight of oat husks ad lib. during the whole of the preceding lactation. Certain blood and urine constituents were also measured. Loss of body water was significantly less (P less than 0.05) than weight loss of fasted animals, but body water losses were considerable in six of the eight animals. Excretion of urinary nitrogen, urea and creatinine and levels of plasma urea were higher, while levels of plasma non-esterified fatty acids and the hydroxyproline index were lower 1 week after weaning compared with values obtained on the day following weaning. These results indicate that in addition to water loss, depletion of body tissue, including protein, occurs in the newly-weaned sow.