Date of Graduation

Spring 2021

Degree

Master of Science in Agriculture

Department

College of Agriculture

Committee Chair

Melissa Remley

Abstract

In 2020 Missouri ranked third in beef cattle production and second in hay production. As part of the fescue belt of the United States, Missouri’s agricultural industries rely on tall fescue (Lolium arundinaceum Schreb.) as a main forage crop. Two major disorders in cattle grazing tall fescue are fescue toxicosis and grass tetany. Fescue toxicosis occurs when animals consume toxic ergot alkaloids produced by an endophyte within the tall fescue plants. The most commonly grown tall fescue variety, Kentucky 31, is infected with the toxic endophyte. Varieties containing a novel non-toxic endophyte, such as Estancia, have been developed to avoid fescue toxicosis. Grass tetany is a metabolic disorder caused by low blood magnesium (Mg) in ruminants. Grazing on tall fescue with lower Mg, in the spring and fall, can elevate these symptoms. Increased leaf Mg and calcium (Ca) concentrations, along with decreased levels of leaf potassium (K), reduce the grass tetany ratio [K/(Ca+Mg)], thus reducing the risk for grass tetany. The purpose of this study is to compare leaf nutrient concentrations of Kentucky 31 and Estancia varieties to determine differences in the risk for grass tetany. Established plots of Estancia and Kentucky 31 at the University of Missouri Southwest Research Center in Mount Vernon, Missouri were sampled in the fall of 2020. Upon analysis of the leaf nutrient concentrations, Estancia revealed higher leaf Ca and Mg in comparison to Kentucky 31 across all three months of the study. The increase in Ca and Mg content in Estancia produced a lower grass tetany ratio compared to that of Kentucky 31. Further research is required to determine if these varietal differences are apparent in the spring and when grown under varying soil fertility levels.

Keywords

beef cattle, tall fescue, fescue toxicosis, grass tetany, toxic endophyte, novel endophyte, grass tetany ratio, magnesium

Subject Categories

Agriculture

Copyright

© Macie W. Clark

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