Adsa Logo White Adsa Title White

Estimating gastrointestinal tissue use of postruminally absorbed amino acids using a stable isotope-based approach.

J. M. Prestegaard

420
Estimating gastrointestinal tissue use of postruminally absorbed amino acids using a stable isotope-based approach.
J. M. Prestegaard*, X. Huang, A. C. Hruby, L. M. Campos, M. D. Hanigan. Virginia Polytechnic Institute and State University Blacksburg, VA.

Postruminal amino acid (AA) flow is often believed to be readily available to the animal after it is absorbed across the small intestinal lumen into the bloodstream. However, several studies have demonstrated that AA appearance in the portal drained viscera may vary upwards of 80% relative to what appears in duodenal digesta. As such, gut tissues may utilize absorbed AA before use by other tissues. The objective of this study was to estimate use of Lys, Met and His by gastrointestinal tissues post-absorption. To measure this, 6 dry Holstein cows were used in a 6 × 6 Latin square design in 10-d periods. Cows were all fed a basal ration formulated for high-producing lactating cows. Cows were assigned to 1 of 6 treatments: the basal diet alone (BASE), BASE plus a 54-h abomasal infusion of a mixture of unprotected essential amino acids (EAA), and 4 treatments that consisted of BASE plus inclusions of prototypical ruminally-protected AAs. Ruminally-protected Met (M1, M2, M3, M4), Lys (K1, K2, K3, K4) and His (H1, H2) prototypes were used in 4 treatments to evaluate respective plasma appearances: MKH1 = M1+K1+H1; MKH2 = M2+K2+H2; MK1 = M3+K3; MK2 = M4+K4. On d10 of each period, an 8-h jugular infusion of a mixture of 13C-labeled AA was administered. Isotope ratios were determined via GC-IRMS for each EAA from collected plasma samples and a dynamic 4-pool model was fit to observed EAA isotope ratios to derive post-absorptive entry rates. Plasma appearance of AAs was derived through linear regression of derived entry rates on dietary or abomasally infused EAA. Plasma appearance of Lys from EAA was 93.7% (P = 0.06 ± 0.02), indicating average first-pass Lys loss was 6.3% if we assume the digestibility of EAA was 100%. First-pass loss of Met and His were 16.2% and 9.30%, respectively, as plasma appearances were 83.8% for Met (P = 0.22 ± 0.66) and 90.7% for His (P = 0.19 ± 0.67). Although gut tissue use may not be the sole contributor to first-pass AA loss, accounting for such post-absorptive factors allows for better prediction of dietary AA utilization in ration balancing models.

Keywords: amino acids, metabolism, modelling.