Evaluation of Resistance to Fescue Toxicosis in Purebred Angus Cattle Utilizing Animal Performance and Cytokine Response

Abstract

Fescue toxicosis is a multifaceted syndrome common in cattle grazing endophyte-infected tall fescue; however, varying symptomatic responses potentially imply genetic tolerance to the syndrome. It was hypothesized that a subpopulation of animals within a herd would develop tolerance to ergot alkaloid toxicity. Therefore, the goals of this study were to develop selection criteria to identify tolerant and susceptible animals within a herd based on animal performance, and then examine responsive phenotypic and cytokine profiles to fescue toxicosis. Angus cows grazed endophyte-infected tall fescue at two locations for 13 weeks starting in mid-April 2016. Forage measurements were collected to evaluate ergot alkaloid exposure during the study. A post hoc analysis of animal performance was utilized to designate cattle into either tolerant or susceptible groups, and weekly physiological measurements and blood samples were collected to evaluate responses to chronic exposure to endophyte-infected tall fescue. Findings from this study support the proposed fescue toxicosis selection method formulated herein, could accurately distinguish between tolerant and susceptible animals based on the performance parameters in cattle chronically exposed to ergot alkaloids, and provides evidence to warrant additional analysis to examine the impact of ergot alkaloids on immune responsiveness in cattle experiencing fescue toxicosis.

Keywords: cow productivity; cytokines; fescue toxicosis; genetic tolerance.

Figure 1

Body weight by treatment over time (weeks): Cows (n = 27) grazing on novel endophyte fescue pastures (EN, non-toxic) had greater body weights compared to grazing endophyte infected (EI, toxic) fescue pastures. Tolerant animals (EI-TOL) had greater average body weight compared to susceptible (EI-SUS) animals, determined by FTSM; (n = 40). The model was significant by location and treatment X location (trt, loc, trt X loc p-values: p < 0.0001).

Figure 2

EI-TOL animals (n = 20) had greater concentrations of GPRASP-1 (A) and VEGFA (B) in peripheral blood compared to EI-SUS animals (n = 20) when chronically exposed to endophyte-infected tall fescue (p < 0.05).

Figure 3

Experimental timeline used during cow performance phase of data collection from late-April to late-July 2016.

Figure 4

Graphical representation of the Fescue Toxicosis Selection Method (FTSM) to select the top 20 tolerant (EI-TOL) and 20 susceptible (EI-SUS) animals for further investigation within the entire population. (A) Displays the ranking of growth performance for the entire population (n = 149) observed over the 13-week period. (B) Displays the deviation in growth performance between the tolerant (n = 20) and susceptible (n = 20) animals over the 13-week period.