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. 2023 May 18;15(5):343.
doi: 10.3390/toxins15050343.

Behavioral and Physiological Alterations in Angus Steers Grazing Endophyte-Infected Toxic Fescue during Late Fall

Ignacio M Llada  1   2 , Jeferson M Lourenco  3 , Mikayla M Dycus  3 , Jessica M Carpenter  2 , Garret Suen  4 , Nicholas S Hill  5 , Nikolay M Filipov  1   2
Affiliations

Behavioral and Physiological Alterations in Angus Steers Grazing Endophyte-Infected Toxic Fescue during Late Fall

Ignacio M Llada et al. Toxins (Basel). .

Abstract

Fescue toxicosis is caused by grazing ergot alkaloid-producing endophyte (Epichloë coenophiala)-infected tall fescue (E+). Summer grazing of E+ leads to decreased productivity, associated impaired thermoregulation, and altered behavior. The goal of this study was to determine the role of E+ grazing-climate interaction on animal behavior and thermoregulation during late fall. Eighteen Angus steers were placed on nontoxic (NT), toxic (E+) and endophyte-free (E-) fescue pastures for 28 days. Physiological parameters, such as rectal temperature (RT), respiration rate (RR), ear and ankle surface temperature (ET, AT), and body weights, were measured. Skin surface temperature (SST) and animal activity were recorded continuously with temperature and behavioral activity sensors, respectively. Environmental conditions were collected using paddocks-placed data loggers. Across the trial, steers on E+ gained about 60% less weight than the other two groups. E+ steers also had higher RT than E- and NT, and lower SST than NT post-pasture placement. Importantly, animals grazing E+ spent more time lying, less time standing, and took more steps. These data suggest that late fall E+ grazing impairs core and surface temperature regulation and increases non-productive lying time, which may be partly responsible for the observed decreased weight gains.

Keywords: Epichloë coenophiala; fescue toxicosis; pasture behavior; tall fescue; thermoregulation.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
(A) Temperature (tail skin surface and environmental temperature, in °C)-treatment interaction during specific hours for the 28-day study period. (B) Tail Skin surface temperature (SST) 1 h before sunrise (6:00), the beginning of sunrise (7:00), beginning of sunset (18:00), and 1 h after sunset (19:00). (*) indicates a significant difference between treatment groups (p ≤ 0.05). Data are presented as mean ± SEM.
Figure 2
Figure 2
(A) Average 24-h behavioral activity throughout the trial. (A) Standing time (min/h)-left side, lying lime (min/h)-middle, and steps (n/h)-right side of Angus steers grazing E− (n = 6), NT (n = 6) and E+ (n = 6) tall fescue. (B) One-hour windows from (A); top panels: standing and lying time on specific hours of the study (6:00, 7:00, 18:00, and 19:00). Bottom panels: number of steps for the same hours. (*) indicates a significant difference between treatment groups (p ≤ 0.05) for these variables. Data are presented as mean ± SEM.
Figure 3
Figure 3
(A) Body weight (kg) of Angus steers before (pre) pasture placement, (B) Cumulative (kg) and Average daily weight gains (ADG; kg/day), after 28 days of grazing E− (n = 6), NT (n = 6) or E+ (n = 6) tall fescue. (*) indicates a significant difference between treatment groups (p ≤ 0.05). Data are presented as mean ± SEM.
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