Aggregate risk study of exposure to endophyte-infected (Acremonium coenophialum) tall fescue as a risk factor for laminitis in horses

Barton W. Rohrbach From the Departments of Large Animal Clinical Sciences (Rohrbach, Green) and Comparative Medicine (Oliver), College of Veterinary Medicine, and The Agricultural Experiment Station (Schneider), University of Tennessee, Knoxville, TN 37901-1071.

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Eleanor M. Green From the Departments of Large Animal Clinical Sciences (Rohrbach, Green) and Comparative Medicine (Oliver), College of Veterinary Medicine, and The Agricultural Experiment Station (Schneider), University of Tennessee, Knoxville, TN 37901-1071.

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Jack W. Oliver From the Departments of Large Animal Clinical Sciences (Rohrbach, Green) and Comparative Medicine (Oliver), College of Veterinary Medicine, and The Agricultural Experiment Station (Schneider), University of Tennessee, Knoxville, TN 37901-1071.

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John F. Schneider From the Departments of Large Animal Clinical Sciences (Rohrbach, Green) and Comparative Medicine (Oliver), College of Veterinary Medicine, and The Agricultural Experiment Station (Schneider), University of Tennessee, Knoxville, TN 37901-1071.

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SUMMARY

Loline and ergot alkaloids found in endophyte-infected (Acremonium coenophialum) tall fescue (eitf) cause vasoconstriction of equine vessels in vitro. An aggregate risk study was used to evaluate the association between horses exposed to eitf and development of laminitis. Veterinary teaching hospitals participating in the Veterinary Medical Data Base were grouped by whether equine accessions were likely to have been at high, moderate, or low risk for exposure to eitf. From 1980-1990, there were 185,781 accessions, of which 5,536 had diagnosis of laminitis. Proportion of equine accessions with laminitis reported by veterinary teaching hospitals for high, moderate, and low risks, were 3.41, 3.04, and 2.00 cases/100 accessions, respectively (P < 0.0001). Comparison of the proportion of accessions with laminitis in the high- and moderate-risk groups with that in the low-risk group revealed significant differences between risk groups over all months (P = 0.063) and differences from month to month within risk groups (P = 0.0001). If the difference among risk groups is attributed entirely to exposure to eitf, the population-attributable risk is 7 cases/1,000 admissions, or 15% of all admissions for laminitis at veterinary teaching hospitals in our data base. Preliminary data support an association between horses exposed to eitf and increased risk of laminitis; however, studies at the individual animal level are indicated to confirm this hypothesis.

SUMMARY

Loline and ergot alkaloids found in endophyte-infected (Acremonium coenophialum) tall fescue (eitf) cause vasoconstriction of equine vessels in vitro. An aggregate risk study was used to evaluate the association between horses exposed to eitf and development of laminitis. Veterinary teaching hospitals participating in the Veterinary Medical Data Base were grouped by whether equine accessions were likely to have been at high, moderate, or low risk for exposure to eitf. From 1980-1990, there were 185,781 accessions, of which 5,536 had diagnosis of laminitis. Proportion of equine accessions with laminitis reported by veterinary teaching hospitals for high, moderate, and low risks, were 3.41, 3.04, and 2.00 cases/100 accessions, respectively (P < 0.0001). Comparison of the proportion of accessions with laminitis in the high- and moderate-risk groups with that in the low-risk group revealed significant differences between risk groups over all months (P = 0.063) and differences from month to month within risk groups (P = 0.0001). If the difference among risk groups is attributed entirely to exposure to eitf, the population-attributable risk is 7 cases/1,000 admissions, or 15% of all admissions for laminitis at veterinary teaching hospitals in our data base. Preliminary data support an association between horses exposed to eitf and increased risk of laminitis; however, studies at the individual animal level are indicated to confirm this hypothesis.

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