Pattern of postruminal administration of L-tryptophan affects blood serotonin in cattle

Authors: VALENTE, ERITON - Western Paraná State University; Klotz, James; AHN, GYUCHUL - University Of Kentucky; HARMON, DAVID - University Of Kentucky

Submitted to: Domestic Animal Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2020
Publication Date: 9/20/2021
Publication URL: https://handle.nal.usda.gov/10113/7139244
Citation: Valente, E.E., Klotz, J.L., Ahn, G., Harmon, D.L. 2021. Pattern of postruminal administration of L-tryptophan affects blood serotonin in cattle. Domestic Animal Endocrinology. 74. Article 106574. https://doi.org/10.1016/j.domaniend.2020.106574.
DOI: https://doi.org/10.1016/j.domaniend.2020.106574

Interpretive Summary: There is little information on tryptophan use and infusion in cattle. Increasing the available tryptophan has the potential to alter the production of serotonin and thus energy metabolism. This could translate into increased feed efficiency in livestock. The objective of this study was to determine if serotonin metabolism is altered through the supplementation of the precursor amino acid tryptophan. Tryptophan was abomasally infused in 3 different patterns, continuous infusion, pulse dose once a day, or pulse dose twice a day. Urine and blood were sampled. Serum tryptophan and serotonin increased in all infusion treatments, but only serotonin increased in the pulse dose treatments. This initial study has demonstrated that it is possible to increase circulating serotonin with infusion of tryptophan and at this point will be primarily of interest to other scientists.

Technical Abstract: Serotonin (5-HT) has many important functions in both central and peripheral nervous systems. Although it has been demonstrated that manipulation of serotonin metabolism is possible in many species, there is limited information about tryptophan (TRP) use in cattle and with contradicting results. Furthermore, there is no study evaluating administration pattern on 5-HT synthesis. The objective of this study was evaluate if intra-abomasal infusion patterns of TRP can increase 5-HT in the blood. Eight Holstein steers fitted with ruminal cannulas in a replicated 4 x 4 Latin Square design received intra-abomasal water infusion (Control) or intra-abomasal TRP infusion (50 mg/kg) in three different patterns: a pulse infusion once a day (Pulse Once), pulse infusion twice a day (Pulse Twice) or continuous infusion (Continuous). The steers were fed every 2 h and blood was collected from a jugular vein catheter every 4 h until 24 h after the initial infusion. Urine was was collected for the entire 24 h period. TRP, 5-HT and kynurenine were analysed in both serum and plasma while glucose was analysed only in the plasma. Urine was analysed for 5-Hydroxyindoleacetic acetic contents. Both serum TRP and kynurenine were increased (P < 0.05) by all TRP infusion treatments, but concentrations in pulse dose treatments were greater than continuous infusion. Serum 5-HT increased (P < 0.05) with both pulse TRP infusion treatments; however, the continuous TRP infusion did not increase the serum 5-HT. Plasma 5-HT and glucose had a tendency to increase with TRP pulse infusions. The urinary 5-hydroxyindoleacetic acid excretion was highest for pulse dose treatments. An acute supply of TRP in one or two daily doses increases circulating 5-HT which may have effects on energy metabolism.