Veterinarians need to sedate or even fully anesthetize horses for routine veterinary care as well as emergency procedures. Here, John A.E. Hubbell, DVM, MS, Dipl. ACVA, took five to answer five of our top questions on the topic of equine anesthesia and sedation. Hubbell, widely considered one of the most experienced equine anesthesiologists in the industry, currently serves as Rood & Riddle Equine Hospital’s chief of anesthesia, in Lexington, Kentucky.
The Horse: When were sedatives popularized in equine medicine?
Hubbell: Today’s sedatives were developed between the 1970s and 1990s. These medications include xylazine, acepromazine, detomidine, romifidine, and butorphanol. Before then, less potent medications were used, as well as local anesthetics like procaine and later lidocaine and mepivacaine to desensitize the skin. Prior to the advent of chemical restraint, physical restraint, including twitches and casting harnesses, played a large role in any procedure.
The Horse: How safe are these sedatives?
Hubbell: Our sedatives have a rapid onset, three to five minutes, so they can be dosed “to effect.” Foals might lie down when sedated, but the vast majority of adult horses remain standing even when heavily sedated. If an excessive dose is inadvertently administered, the duration of the sedation increases but the effect usually remains the same.
Safety for the horse, the veterinarian, and the handler are enhanced compared to earlier times because there is less reliance on physical restraint. In terms of the horse’s safety, occasionally a horse will experience choke if they are allowed to eat before the drugs wear off, and instances of aggression (usually biting the handler) have been reported after xylazine and detomidine administration.
The Horse: How safe is anesthesia?
Hubbell: Short-term anesthesia (20 to 30 minutes of recumbency) is currently the safest it has ever been, but it is still not without risk. Larger horses are at somewhat greater risk, primarily because it is more difficult to assist them to their feet during recovery. Horses that are not accustomed to being handled also have a greater risk, as well as older horses (greater than 17 to 20 years of age).
The Horse: Under what circumstances would you refer a horse due to safety concerns associated with sedation/anesthesia?
Hubbell: Most often, cases are referred because of the procedure being performed rather than the risk of sedation or anesthesia. For any horse, the longer the anesthetic duration, the greater the risk, particularly procedures extending beyond 90 minutes.
The Horse: Do vets use a “one size fits all” protocol for sedation/anesthesia?
Hubbell: Many equine veterinarians have developed different dosing regimens for different breeds or types of horses based on their experiences.
Minimal data are available to directly support variations between breeds, but here are some observations I made during my career:
- The atmosphere of the stable/training facility plays a role in the amount of sedation required for a given procedure.
- If the owner or trainer works with the horse routinely and teaches it to behave appropriately, the horse will typically require smaller doses of sedative drugs.
- Draft horse breeds and American Saddlebreds require smaller doses of xylazine and detomidine (mg/kg basis) to produce useful sedation compared to mustangs, Arabian horses, and Appaloosas.