Comparison of the Dual Isotope Tracer Approach with Oro-Ileal Balance Method for Determination of Amino Acid Digestibility in Cannulated Pigs.

Background: The dual isotope tracer approach was developed as a less invasive alternative for the measurement of ileal amino acid (AA) digestibility.

Objectives: This study aimed to validate the dual isotope tracer approach with the standardized oro-ileal balance method in growing pigs.

Methods: Eight pigs were fitted with jugular catheters and ileal T-cannulas. On the test day, feed containing intrinsically labeled ¹⁵N-milk protein and ¹³C-spirulina was provided every half hour for 240 min. Ileal digesta and 10 jugular blood samples were collected between 0 min and 540 min. Digesta samples were analyzed for isotopic enrichment, AA, and titanium concentrations for balance method calculations. Serum AA isotopic enrichment was measured for dual stable isotope tracer calculations.

Results: Using the oro-ileal balance method, the mean ileal AA digestibility of milk protein concentrate was 97.8 ± 0.59% and of spirulina 81.5 ± 2.44% (mean ± standard deviation). Lysine digestibility was specifically evaluated, as it does not transaminate. Lysine digestibility of milk protein concentrate calculated according to the dual isotope tracer approach was 88.9 ± 8.35%, 9% point lower than the value obtained with the oro-ileal method (98.1 ± 0.36, P = 0.04). Moreover, Bland-Altman analysis showed that the difference between methods was higher, with lower mean lysine digestibility.

Conclusions: This study observed differences between the dual isotope tracer approach and the oro-ileal balance method for estimating lysine digestibility under the current experimental conditions with 6 pigs. This result may be due to methodological issues. Considering the use of ¹⁵N protein, conclusions on other AA that do not transaminate could not be drawn.