Objective: To determine whether microchips used for identification migrate after implantation in horses, donkeys, and mules.
Design: Prospective study.
Animals: 53 horses, donkeys, and mules.
Procedure: Twenty horses that had had microchips implanted in the nuchal ligament at a veterinary teaching hospital from 1996 through early 2000 were included (group 1), and the poll-to-withers distance and location of the microchip were determined, measured, and recorded. Additionally, the poll-to-withers distance was measured in 16 horses, 12 donkeys, and 5 mules (group 2), and microchips were implanted in the nuchal ligament on the left side of the neck. Forty-two to 67 days after implantation, the location of the microchip was determined, measured, and recorded.
Results: Microchips implanted in the nuchal ligament < or = 4 years previously did not migrate. All microchips were detected with a multimode identification tag reader from the left side of the neck in the midcervical region, and microchips were located at the midpoint between the poll and withers for all 53 horses, donkeys, and mules.
Conclusions and clinical relevance: Microchips implanted in the nuchal ligament < or = 4 years earlier did not migrate in horses. Microchips may be useful for identification in horses.