Ergot alkaloids reduce circulating serotonin in the bovine

Authors: VALENTE, ERITON - Western Paraná State University; Klotz, James; AHN, GYUCHUL - University Of Kentucky; MCLEOD, KYLE - University Of Kentucky; HERZING, HANNAH - University Of Kentucky; KING, MINDY - University Of Kentucky; HARMON, DAVID - University Of Kentucky

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/9/2020
Publication Date: 11/14/2020
Citation: Valente, E.E., Klotz, J.L., Ahn, G., McLeod, K.R., Herzing, H.M., King, M., Harmon, D.L. 2020. Ergot alkaloids reduce circulating serotonin in the bovine. Journal of Animal Science. 98(12):skaa362. https://doi.org/10.1093/jas/skaa362.
DOI: https://doi.org/10.1093/jas/skaa362

Interpretive Summary: It has been shown that ergot alkaloids, the toxins responsible for causing fescue toxicosis, interact with serotonin receptors to cause some of the observed symptoms. It is not known if this receptor interaction by the toxins also has a feedback influence on levels of serotonin or it's metabolites. The neurotransmitter serotonin has many functions throughout the body and toxin-induced changes in concentrations could have undesirable systemic effects. Two experiments were conducted that evaluated the dose of ergovaline (an ergot alkaloid) and the bioavailability of ergovaline in tall fescue seed on levels of serotonin and it's metabolites in cattle. Ergovaline caused a decrease in blood serotonin that decreased further with higher ergovaline concentrations. The seed used to provide the ergovaline all had the same bioavailability and all induced a decrease in serotonin levels. These findings are of use to researchers working towards understanding the whole impact of ergot alkaloids on physiology of livestock that consume them.

Technical Abstract: Ergot alkaloids can interact with many serotonin (5-HT) receptors provoking many physiological responses. However, it is unknown whether ergot alkaloids directly influence 5-HT or its metabolites. Thus, two experiments were performed to evaluate the effect of ergot alkaloid feeding on 5-HT metabolism. In Experiment 1, 12 Holstein steers (260 ± 3 kg BW) were used in a completely randomized design. The treatments were the dietary concentration of ergovaline: 0, 0.862, and 1.282 mg/kg of diet. The steers were fed ad libitum, kept in light and temperature cycles mimicking the summer, and had blood sampled before and 15 d after receiving the treatments. The consumption of ergot alkaloids provoked a linear decrease (P=0.004) in serum 5-HT. However, the serum 5-hydroxytryptophan and 5-hydroxyindoleacetic acid did not change (P>0.05) between treatments. In Experiment 2, four ruminally cannulated Holstein steers (318 ± 3 kg BW) were used in a 4×4 Latin square design to examine the difference between seed source on 5-HT metabolism. Treatments were: control - tall fescue seeds free of ergovaline, KY 32 seeds (L42-16-2K32); 5Way - endophyte-infected seeds 5 way (L152-11-1739); KY31- endophyte-infected seeds KY 31 (M164-16-SOS) and; Millennium - endophyte-infected seeds 3rd Millennium (L108-11-76). The endophyte-infected seed treatments were all adjusted to provide an ergovaline dosage of 15 µg/kg BW. The basal diet provided 1.5-fold the net energy requirement for maintenance. The seed treatments were dosed directly into the rumen before feeding. The experiment lasted 84 d divided into four periods. In each period, the steers received seeds for 7 d followed by a 14-d washout. Blood samples were collected on d 0 (baseline) and d 7 for evaluating the treatment response in each period. A 24 h urine collection was performed on d 7. Similar to Exp. 1 serum 5-HT decreased (P=0.008) with the consumption of all endophyte-infected seed treatments. However, there was no difference (P > 0.05) between the infected seeds. The urinary excretion of 5-hydroxyindoleacetic acid in the urine was not affected (P > 0.05) by the presence of ergot alkaloids. In conclusion, the consumption of ergot alkaloids decreases serum 5-HT with no difference between the source of endophyte-infected seeds in the bovine. Alkaloid over-stimulation on 5-HT receptors seems to cause changes in synthesis and transport of 5-HT decreasing the circulating concentration.