Impact of endophyte-infected tall fescue seed consumption on endocrine changes associated with intake regulation and post-absorptive metabolism in growing steers

Authors: KING, MINDY - University Of Kentucky; HERZING, HANNAH - University Of Kentucky; MCLOED, KYLE - University Of Kentucky; Klotz, James; FOOTE, ANDREW - Oklahoma State University; EDWARDS, JANICE - University Of Tennessee; HARMON, DAVID - University Of Kentucky

Submitted to: Domestic Animal Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/9/2024
Publication Date: 7/19/2024
Citation: King, M.E., Herzing, H.M., McLoed, K.R., Klotz, J.L., Foote, A.P., Edwards, J.L., Harmon, D.L. 2024. Impact of endophyte-infected tall fescue seed consumption on endocrine changes associated with intake regulation and post-absorptive metabolism in growing steers. Domestic Animal Endocrinology. 89. Article 106873. https://doi.org/10.1016/j.domaniend.2024.106873.
DOI: https://doi.org/10.1016/j.domaniend.2024.106873

Interpretive Summary: Fescue toxicosis is estimated to be responsible for over $2 billion in annual losses to livestock producers. A large portion of this financial loss for meat animal producers is a consequence of lower weight gains by animals suffering from fescue toxicosis. These lower weight gains are caused by reductions in feed intake. The primary toxin found in tall fescue responsible for fescue toxicosis is ergovaline. This study looked at feeding 3 different levels of ergovaline to cattle on hormones that are responsible for control of feed intake. Steers on the study that received the intermediate and high doses of ergovaline did have lower intake compared to steers that received 0 ergovaline in their diet. Along with a change in feed intake, there were also ergovaline-induced changes in hormones associated with feed intake control. This work will primarily be of interest to other researchers looking to indentify potential mechanisms by which ergovaline causes lower feed intake in cattle.

Technical Abstract: Fescue toxicosis is a syndrome resulting from consumption of endophyte-infected tall fescue and results in substantial economic losses to the beef industry primarily from reduced growth associated with decreased dry matter intake (DMI); however, the mechanisms characterizing this reduction in DMI have yet to be elucidated. The objective of this experiment was to identify endocrine changes associated with intake regulation after consumption of endophyte-infected tall fescue seed (E+). Twelve Holstein steers were stratified by body weight and assigned to 1 of 3 treatments (n=4): 0 ppm ergovaline (ERV), 1.8 ppm ERV, or 2.7 ppm ERV. Treatments were achieved by combining differing proportions of ground E+ and non-endophyte-infected tall fescue seed. Steers were adapted to their diets for 7 d followed by a 7 d DMI collection period. Within treatment, steers were blocked to a sampling day. On each sampling day, blood samples were collected every 20-min for 8 h beginning 1 h before feeding. Intake data was analyzed using the MIXED procedure of SAS 9.4 (SAS Inst. Inc., Cary, NC) with treatment, day, and the interaction as fixed effects. Hormone and metabolite data were similarly analyzed including the fixed effect of treatment, time, and the interaction in addition to a repeated measures analysis and orthogonal contrasts. Dry matter intake was linearly decreased with increasing ERV in the diet (P < 0.0001). Insulin and leptin concentrations exhibited a quadratic effect (P = 0.0176; P = 0.0046). Insulin concentrations were highest for the 2.7 ppm treatment and leptin concentrations were highest for the 1.8 ppm treatment. No differences were detected for active ghrelin or ß-hydroxybuytrate concentrations. Further, steers consuming both the 1.8 and 2.7 ppm ERV treatments had lower prolactin concentrations compared to the 0 ppm treatment (quadratic, P = 0.0190). Glucose concentrations had a tendency for a linear increase as ERV concentrations increased (P = 0.0909). A treatment x time interaction (P = 0.002) was noted in NEFA concentrations, with the 1.8 ppm ERV treatment showing increased pre-feeding concentrations, and the 2.7 ppm ERV treatment exhibiting elevated NEFA concentrations as the post-feeding time progressed. The results suggest that E+ consumption reduces intake likely through alterations in intake-related hormones and post-absorptive metabolism and contributes to our current understanding of E+ effects on intake reduction while providing avenues for future research.