Long-term assessment of horses and ponies post exposure to monensin sodium in commercial feed.
BACKGROUND
Acute monensin intoxication in equids is well described; however, the long-term effects of sublethal intoxication and ability to return to previous use are less well understood. Long-term observations may allow improved estimation of prognosis in cases of sublethal intoxication.


OBJECTIVE
To assess horses and ponies exposed to sublethal amounts of monensin for evidence of chronic sequelae and ability to return to prior/intended use.


METHODS
Twenty-nine horses and 8 ponies were assessed utilising serum biochemistry, treadmill exercise stress testing, electrocardiography, and pre- and post exercise echocardiography > or = 6 weeks after ingestion of monensin-contaminated feed. Animals with evidence of monensin-induced cardiomyopathy were re-examined after a period of rest of > or = 11 months. Follow-up information was obtained by owner telephone interview > or = 52 months after exposure.


RESULTS
During resting echocardiography, 11 animals had reduced/low-normal left ventricular fractional shortening (FS); an increase in FS in 8 of these animals was measured > or = 11 months later. Six animals had reduced or low-normal FS during post exercise echocardiography. Two horses had ventricular premature depolarisations during exercise. Follow-up information was available for 35 animals: 21 returned to athletic/reproductive use, 13 were retired immediately and one died. Mean FS increased significantly (P < 0.001) between initial and second examination in 15 animals that underwent resting echocardiography on 2 occasions.


CONCLUSIONS
Some equids exposed to sublethal doses of monensin may not develop permanent myocardial disease and a return to athletic/reproductive use is possible.


CONCLUSIONS
Exercise stress testing, echocardiography and electrocardiography may be useful for detection and monitoring of cardiac dysfunction in equids exposed to monensin and determining whether a return to athletic/reproductive use is possible.
Hughes
K J
KJ
Faculty of Veterinary Science, University of Sydney 410 Werombi Road, Camden, New South Wales 2570, Australia.
Hoffmann
K L
KL
Hodgson
D R
DR
D000821:Animal Feed / Q000009:adverse effects; D000818:Animals; D001774:Blood Chemical Analysis / Q000662:veterinary; D009202:Cardiomyopathies / Q000139:chemically induced / Q000473:pathology / Q000662:veterinary*; D004305:Dose-Response Relationship, Drug; D004452:Echocardiography / Q000662:veterinary; D004562:Electrocardiography / Q000662:veterinary; D005080:Exercise Test / Q000662:veterinary; D005260:Female; D005500:Follow-Up Studies; D005506:Food Contamination; D006734:Horse Diseases / Q000139:chemically induced* / Q000473:pathology; D006736:Horses; D007476:Ionophores / Q000506:poisoning*; D008297:Male; D008985:Monensin / Q000506:poisoning*; D013997:Time Factors
D007476:Ionophores; D008985:Monensin