Date of Award

8-2013

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

John C Waller

Committee Members

Gary E. Bates, James B. Neel, Justin D. Rhinehart

Abstract

Tall fescue, Lolium arundinaceum (Schreb.) Darbysh., is the predominate pasture grass in the mid-south region of the United States. The most dominant cultivar of tall fescue in the region is Kentucky-31. Kentucky-31 is infected with an endophytic fungus Neotyphodium coenophialum (Morgan-Jones and Gams), which is responsible for the cultivar’s drought tolerance, persistence under stressful conditions, and adaptation to multiple soil types. However, the endophyte is also responsible for producing toxic alkaloids that cause tall fescue toxicosis. Symptoms of fescue toxicosis are retention of winter hair coat, elevated body temperature, increased respiratory rate, reduced average daily gain (ADG), lower serum prolactin levels, and reduced reproductive performance. Four approaches proposed to reduce or eliminate tall fescue toxicosis are to use endophyte-free cultivars, dilute the toxins, dietary supplementation, or switch to novel endophyte cultivars. In this study, Jesup MaxQ, a novel endophyte-infected tall fescue, was investigated at two stocking rates at Blount Livestock Unit of the East Tennessee Research and Education Center. Tall fescue was renovated with white clovers to evaluate the persistence of the clover cultivars and to investigate the interactions of clovers with Kentucky-31 and Jesup MaxQ. Both fescue cultivars were grazed at different stocking rates to provide information needed by beef producers desiring to optimize animal performance. In addition, animal performance was measured for beef steers grazing tall fescue cultivars with and without toxic endophytes. Differences in stocking rate were not found in this study. Patriot clover was more persistent that Regal clover in Ky-31 E+ tall fescue. Animal performance was similar when steers grazed Jesup MaxQ and endophyte-free tall fescue and superior to those grazing endophyte-infected tall fescue. Steers grazing E+ tall fescue exhibited the typical performance, hair scores, and prolactin levels found when cattle are experiencing tall fescue toxicosis

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