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Effects of oral tetrachlorvinphos fly control (Equitrol®) administration in horses: Physiological and behavioural findings

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Abstract

Highly reactive horses may pose risks to humans involved in equestrian activities. Among the factors that may affect horses’ reactivity to external stimuli are pesticides used for fly control in equine facilities. The organophosphorus (OP) insecticide tetrachlorvinphos (TCVP) is used as a feed-through larvicide to prevent completion of the fly larval life cycle in horse manure. TCVP exerts its effect by inhibiting the enzyme cholinesterase (ChE) leading to the accumulation of the neurotransmitter acetylcholine (AChE) in synapses of the central and peripheral nervous systems. The aim of the present study was to investigate alterations of whole-blood ChE levels associated with feeding a commercially available product (Equitrol, Farnam Companies, Inc.) to horses for fly control. A second aim was to report neurological, physiological and behavioural findings in addition to profiles of selected immune markers (IFN-γ, IL-12p40 and COX-2) and serum thyroid hormones during and after a 30-day treatment period of TCVP feeding. The results indicated significant decreases in whole-blood ChE activity and concomitant behavioural alterations, manifested as increased reactivity and decreased controllability in treated horses. No changes were detected in physiological or neurological parameters, immune markers or thyroid hormones in treated (n = 6) or control (n = 4) horses during the course of the study.

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Authors and Affiliations

  1. Behaviour Service, Veterinary Medical Teaching Hospital, University of California, Davis, California, USA

    J. Berger

  2. San Luis Rey Equine Hospital, 4211 Holly Lane, Bonsall, CA, 92003-7106, USA

    S. Valdez

  3. California Animal Health and Food Safety Laboratory, University of California, Davis, California, USA

    B. Puschner

  4. IDEXX Laboratories, 2825 KOVR Drive, West Sacramento, CA, 95605, USA

    C. M. Leutenegger

  5. Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, California, USA

    I. A. Gardner

  6. Department of Medicine and Epidemiology, Lucy Whittier Molecular and Diagnostic Core Facility, School of Veterinary Medicine, University of California, Davis, California, USA

    J. E. Madigan

  7. Veterinary Medicine and Epidemiology, University of California, Tupper Hall 2108, Davis, CA, 95616, USA

    J. Berger

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  1. J. Berger
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  2. S. Valdez
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  3. B. Puschner
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  4. C. M. Leutenegger
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  5. I. A. Gardner
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  6. J. E. Madigan
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Correspondence to J. Berger.

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Berger, J., Valdez, S., Puschner, B. et al. Effects of oral tetrachlorvinphos fly control (Equitrol®) administration in horses: Physiological and behavioural findings. Vet Res Commun 32, 75–92 (2008). https://doi.org/10.1007/s11259-007-9004-z

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  • DOI: https://doi.org/10.1007/s11259-007-9004-z

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