Unusual reaction following overdose of xylazine in a mare
Groenendyk, J.; Hall, L.W.
Veterinary Record 124(19): 511
1989
ISSN/ISBN: 0042-4900 PMID: 2756622 Document Number: 330724
A quiet, healthy 4.5-year-old Standardbred mare weighing 370 kg was anaesthetised for an operation. Xylazine was injected into the left jugular vein through an intradermal and subcutaneous infiltration of mepivicaine. After an injection of 400 mg of xylazine had produced only drooping of the mare's head, the injection was continued to try and obtain the required deep sedation. When 800 mg of xylazine had been administered the mare suddenly staggered and became excited. The injection was stopped immediately. The mare showed dilation of the pupils, staring eyes, head-up stance with pricked ears, and an inclination to walk. Her pulse rate was about 30 beats/minute and breathing rapid. She paid no attention to words of command but was unduly sensitive to environmental noise. Several attempts were made before the successful injection of thiopentone. The mare became recumbent after about 55 seconds and subsequent halothane anaesthesia was unevenful. After the operation the mare recovered with very mild ataxia. It is suggested that one possible reason for the excitement was background noise, which, although not excessive, may have disturbed the mare at a critical time.