Authors
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Abstract
Objective—To determine whether cattle exposed to heat stress alone or heat stress while consuming endophyte-infected fescue (EIF) have lower wholeblood (WB) concentrations of glutathione (GSH).
Animals—10 Simmental cows.
Procedure—Cows were sequentially exposed to thermoneutral (TN; 2 weeks; 18 C, 50% relative humidity [RH]), heat stress (HS; 2 weeks; alternating 4-hour intervals at 26 and 33 C; 50% RH), and heat stress while consuming EIF (10 µg of ergovaline/kg/d; 2 weeks; HS + EIF). Blood samples were collected after each period and tested for GSH and oxidized glutathione (GSSG) concentrations.
Results—Feed consumption was similar when data were analyzed for time points at which WB concentrations of GSH or GSSG were determined. However, significant effects of treatment, cow, days exposed to heat, cow-by-treatment interaction, and treatment-bydays exposed to heat interaction were detected when data were considered simultaneously. Mean ± SD hematocrit for TN, HS, and HS + EIF were 35.3 ± 3, 33.3 ± 2, and 37.1 ± 3%, respectively. Mean WBGSH concentrations for TN, HS, and HS + EIF were 3.2 ± 0.65, 2.7 ± 0.62, and 2.4 ± 0.56 mmol/L of RBC, respectively. Reduced WBGSH concentrations were associated with reduced feed intake during the later part of each heat period.
Conclusion and Clinical Relevance—Decreased GSH and increased GSSG concentrations were evident during heat stress, especially when cattle consumed EIF. These were associated with reduced feed intake during heat stress. Heat stress, reductions in feed intake, and thermoregulatory effects of EIF may induce oxidative stress in cattle. (Am J Vet Res 2002;63:799–803)
