Alterations in hemograms and serum biochemical analytes of steers after prolonged consumption of endophyte-infected tall fescue

The objective of the current study was to delineate changes that occur in s erum analytes and blood cellular elements in cattle that graze endophyte-in fested (Neotyphodium coenophialum) tall fescue. Tall fescue is grown on mor e than 35 million acres (14.2 million ha) of pasture in the United States, and three-fourths of the pastures are infected with the endophyte at a 60% or greater level. Tall fescue toxicosis caused by endophyte-produced ergot alkaloids continues to be the most important grass-related disease in the U nited States, in terms of economic loss to animal producers. However, the a gronomic attributes of tall fescue make it an attractive forage species bec ause of its ability to withstand cool temperatures, drought, poor soil cond itions, and intensive defoliation from herbivore spec:ies, including insect s. Tall fescue toxicosis is a complex disease and the need exists to unders tand the mechanisms of the toxic effects in order to institute effective, p rophylactic control measures. Our group previously reported changes that oc cur in serum biochemical analytes of cattle that graze endophyte-infected t all fescue. An additional year's worth of data have been added, strengtheni ng and corroborating these data. Consistent and significant changes associa ted with tall fescue toxicosis during the 3-yr study included decreased ser um concentrations of cholesterol, globulin (increased albumin/globulin rati o), prolactin, total protein, and copper. The activity of alanine aminotran sferase was decreased in serum, whereas an increase in serum concentrations of creatinine and total bilirubin occurred. The present report also docume nts comparative hemograms of cattle that grazed endophyte-infected or endop hyte-free tall fescue over a prolonged period. The mean erythrocyte counts were increased in cattle that grazed endophyte-infected tall fescue, wherea s mean corpuscular hemoglobin and mean corpuscular volume were decreased, a s were mean eosinophil counts. Thus, repeatable changes have been identifie d that occur in serum biochemical and blood cellular values of cattle grazi ng endophyte-infected tall fescue that will aid in understanding the pathog enesis of the disease. In addition, these consistently altered parameters c an be used to assess the effectiveness of potential prophylactic treatments .