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Interpretive Summary: Endophyte-infected fescue fed to stocker steers

By: Jackie Walling
Courtesy of American Society of Animal Science

A recent article published in the Journal of Animal Science evaluated the effects of supplemental crude protein (CP) on growth and physiological responses in stocker steers experiencing fescue toxicosis. Cattle contract fescue toxicosis by ingesting endophyte-infected tall fescue, most commonly, ergot alkaloids. Consuming infected grasses while in the growth stage could compromise steer performance.

The experiment lasted 56 days and 36 Angus steers were divided into four groups: EF-14 (endophyte-free/14% CP); EF-18 (endophyte-free/18% CP); EI-14 (endophyte-infected/14% CP); and EI-18 (endophyte-infected/18% CP).

According to ergovaline levels (responsible for toxicity), a low to moderate level of toxicosis was induced within a controlled feeding setting. Previous studies show fescue reduces ADG when DMI remains the same, but this study showed no difference in DMI, BW, ADG, F: G, and BCS across treatment groups. Supplementation of protein had no effect on growth performance. This was likely influenced by feeding cattle based on a percent of body weight. In a pasture setting, feed intake fluctuates, and protein supplementation is more apt to influence growth measures.

EI groups had higher values for hair shedding score, respiratory rate, rectal temperature, and surface temperature, which are characteristic of fescue toxicosis. The surface temperature suggests cooling by vasodilation, which was highest in EI-14. EI-18, however, did not have elevated surface temperatures, which suggests heat stress and the inability to take in nutrients (protein) properly.

Hemodynamic measures showed treatment interactions. EI-18 had the slowest heart rate and the smallest caudal vein diameter. EF-14EF-18, and EI-18 had similar caudal artery diameters that were smaller than EI-14. The hematocrit level was not different between EI-18 and EF-14 but was reduced compared to EF-18 and EI-14.

Overall, protein supplementation was not beneficial for the level of fescue toxicosis induced. Growth performance and physiological symptoms remained unaffected, and higher levels of CP diminished hemodynamic measures.

To view the full article, visit the Journal of Animal Science.

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