Cattle grazing tall fescue (Festuca arundinacea Schreb.) often develop fescue toxicosis. This condition is thought to be caused by ergot alkaloids produced by the endophyte Neotyphodium coenophialum. Endophytes from wild tall fescue plants, which do not produce ergot alkaloids, were transferred into the endophyte-free tall fescue germplasm, HiMag. The novel associations also lacked the ability to produce ergot alkaloids. Our objective was to determine whether cattle grazing these novel endophyte associations showed signs of fescue toxicosis. At the Fayetteville, Arkansas location, tester steers (n = 72) were assigned to one of four pasture treatments: endophyte-free HiMag tall fescue (HiMag-); 'Kentucky-31' tall fescue infected with its native, toxic endophyte (KY+); and two novel endophyte-infected tall fescue associations, HiMag4 and HiMag9. At the Mount Vernon, Missouri location, steers (n = 54) were used to test three of the four cultivars (HiMag9 was not tested). Ergot alkaloid concentrations in the forage of HiMag4 and HiMag9 were low or undetectable. Respiration rate, rectal temperature, ADG, and hair scores were measured during the grazing period. Blood was collected via jugular venipuncture and used for prolactin, aspartate aminotransferase, alkaline phosphatase (ALP), lactate dehydrogenase (LDH), cholesterol, triglyceride, and creatinine analysis. Weight gains by steers grazing HiMag4 and HiMag9 did not differ from those of steers grazing HiMag-, but were greater than gains (P < 0.05) by steers on the KY+ treatment. Steers grazing KY+ had higher (P < 0.05) respiration rates, rectal temperatures, and hair scores than did steers grazing novel endophyte and HiMag- pastures. Prolactin, ALP, cholesterol, LDH, and triglycerides all were suppressed (P < 0.05) in steers grazing KY+ compared with steers grazing novel endophyte and HiMag- pastures. Steers grazing the novel endophyte tall fescues did not suffer from the decreased weight gains and toxicities associated with fescue toxicosis, resulting in enhanced animal production.

Cattle grazing tall fescue (Festuca arundinacea Schreb.) often develop fescue toxicosis. This condition is thought to be caused by ergot alkaloids produced by the endophyte Neotyphodium coenophialum. Endophytes from wild tall fescue plants, which do not produce ergot alkaloids, were transferred into the endophyte-free tall fescue germplasm, HiMag. The novel associations also lacked the ability to produce ergot alkaloids. Our objective was to determine whether cattle grazing these novel endophyte associations showed signs of fescue toxicosis. At the Fayetteville, Arkansas location, tester steers (n = 72) were assigned to one of four pasture treatments: endophyte-free HiMag tall fescue (HiMag-); 'Kentucky-31' tall fescue infected with its native, toxic endophyte (KY+); and two novel endophyte-infected tall fescue associations, HiMag4 and HiMag9. At the Mount Vernon, Missouri location, steers (n = 54) were used to test three of the four cultivars (HiMag9 was not tested). Ergot alkaloid concentrations in the forage of HiMag4 and HiMag9 were low or undetectable. Respiration rate, rectal temperature, ADG, and hair scores were measured during the grazing period. Blood was collected via jugular venipuncture and used for prolactin, aspartate aminotransferase, alkaline phosphatase (ALP), lactate dehydrogenase (LDH), cholesterol, triglyceride, and creatinine analysis. Weight gains by steers grazing HiMag4 and HiMag9 did not differ from those of steers grazing HiMag-, but were greater than gains (P < 0.05) by steers on the KY+ treatment. Steers grazing KY+ had higher (P < 0.05) respiration rates, rectal temperatures, and hair scores than did steers grazing novel endophyte and HiMag- pastures. Prolactin, ALP, cholesterol, LDH, and triglycerides all were suppressed (P < 0.05) in steers grazing KY+ compared with steers grazing novel endophyte and HiMag- pastures. Steers grazing the novel endophyte tall fescues did not suffer from the decreased weight gains and toxicities associated with fescue toxicosis, resulting in enhanced animal production.

Literature Summary Study Description Applied QuestionsFull scientific article from which this summary was written begins on page 491 of this issue.Grass tetany (hypomagnesemia) causes economic losses from death or reduced performance of livestock throughout the world. Attempts to reduce the incidence of grass tetany through application of fertilizer Mg have not generally been successful. Dietary Mg supplementation adds to the annual labor and cost of production and does not always ensure all animals receive adequate amounts of the mineral. Selective breeding of forages for higher levels of Mg and lower tetany ratio may offer a long-term solution to the grass tetany problem.Objectives of this study were to evaluate an experimental selection of tall fescue, HiMag, for its ability to reduce the risk of grass tetany through higher Mg concentration and lower tetany ratio of forage, and higher blood serum Mg concentrations of beef cattle under grazing conditions. Twenty, 1-acre pastures on a predominantly Creldon silt loam soil at the Southwest Research Center near Mt. Vernon, MO, were planted to four endophyte-free tall fescue cultivars, AU Triumph, Kentucky-31, Martin, and Mozark, and the experimental cultivar, HiMag. The study consisted of five individual grazing trials using cross-bred beef steers, dry cows, or cow/calf pairs during three autumn and two spring seasons between 1993 and 1995.Forages were sampled each season and analyzed for Mg, Ca, K, and P concentration, and the tetany ratio was calculated. Cattle were weighed at the beginning, middle, and end of each trial to determine average change in weight. Blood serum was collected at each weighing for determination of Mg, Ca, K, and P status of the cattle.Can cool-season forage grasses be selectively bred to reduce the risk of grass tetany?Forage from HiMag tall fescue consistently had higher Mg (22%), Ca (18%), and P (9%) concentration than other tall fescue cultivars. Potassium levels were not different among cultivars. This resulted in a lower tetany ratio for HiMag compared with the other cultivars. Higher Mg concentration (>0.20%) and lower tetany ratio (<2.2) suggest that HiMag tall fescue can reduce risk of occurrence of grass tetany.

One hundred eighty yearling Holstein steers and heifers grazed a series of 2‐acre tall fescue (Festuca arundinacea Schreb.) pastures over a three‐year period. Pastures were infected with Acremonium coenophialum at levels from 3 to 83%. A significant overall relationship between endophyte infection frequency (EIF) and average daily gain (ADG) was described by the equation: ADG (lb/d) = 1.46 − 0.01 × EIF(%). Seasonal variation existed whereby spring‐summer gains were reduced 0.15 lb/head/d for each 10% increase in EIF, while no relationship existed for fall grazing. Although the relationships between EIF and ADG were significant, low R2 values suggest other factors are involved. Still, the general relationship may be useful for estimating animal performance on tall fescue when EIF is known and for making economic decisions regarding management and renovation of infected tall fescue stands.