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Q&A With Leader In Equine Anesthesia

Dr. John Hubbell is considered one of the most experienced equine anesthesiologists in the industry. Currently the chief of anesthesia at Rood and Riddle Equine Hospital in Lexington, Ky., Hubbell was interviewed by The Horse to learn more about equine sedation and anesthesia.

Hubbell told The Horse that the sedatives in use today include xylazine, acepromazine, detomidine, romifidine, and butorphanol, which were developed between the 1970s and 1990s. Prior to the introduction of these drugs, physical restraints were often used in many medical procedures.

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Hubbell reported that the sedatives used today take effect within three to five minutes. Adult horses often remain standing, even when heavily sedated.

With today's lessened reliance on physical restraints, the safety of the horse and the people surrounding him is heightened.

Though anesthesia is the safest it's ever been, there are still risks associated with laying the horse down on its side. Horses that are older (over 17 to 20 years old), those that are large, and those that aren't used to being handled are at the greatest risk of anesthesia complications. Horses in the last two categories, especially, can be difficult to help stand after anesthesia.

Hubbell said procedures that use short-term anesthesia, where the horse is recumbent for 20 to 30 minutes, do not present as many potential issues as procedures which require horses to be under anesthesia for more than 90 minutes.

There are no breed-specific dosing protocols, but Hubbell has found that American Saddlebreds and draft horses often need smaller doses of detomidine or xylazine as compared to Appaloosas, Arabians and Mustangs.

Hubbell has also found that the atmosphere in which he's performing the procedure will affect how much sedation is required. He noted that horses which have been handled regularly and that are taught to behave often require smaller doses of sedative.

Do Sedatives Affect Lameness Exam Outcomes?

Lameness exams on high-energy horses can be difficult to complete, especially if they involve joint or nerve blocks. Occasionally overly exuberant horses must be sedated for the exam to be performed to keep both horse, handler and vet safe. Concerns have been raised that sedating the horse may mask a horse's pain response, and potentially compromise the results of the joint or nerve block and the exam.

A group of Brazilian veterinarians tested the effects of xylazine and xylazine used in conjunction with butorphanol on induced hind-end lameness. Drs. Antônio Alcemar Beck Júnior, Flávio Desessards De La Côrte, Karin Erica Brass, Stéfano Leite Dau, Gabriele Biavaschi Silva and Marina de Aguiar Camillo compared the results of the sedated horses to the results of a control group of horses that did not receive sedation.

The researchers used 16 horses and placed metal clamps around their hoof wall with small screws. The screws were tightened to induce lameness until the horses became a Grade 3 or 4 (out of 5) on the AAEP lameness scale. This was done immediately before the administration of sedation.

Each horse received all three treatments: no sedation, xylazine alone or a combination of xylazine and butorphanol. The scientists concluded that xylazine used alone or in conjunction with butorphanol (at the recommended doses) can be used as chemical restraint without masking lameness intensity. They note that additional research must be done to determine how detomidine and romifidine might interact with butorphanol during hindlimb lameness evaluations.

A New Way To Administer Sedation To Mares

Sedating horses for routine procedures is sometimes necessary. While these drugs are typically administered through intravenous or intra-muscular injection, a new oral gel containing detomidine can be absorbed through the mucous membrane; the ease of administration has made the drug popular among horse owners and caretakers.

The gel is applied under the tongue and absorbed; gel that is swallowed is less effective as it may be broken down during digestion and metabolized before it can induce sedation. Drs. Reza Seddighi, Heather Knych, Sherry Cox, Xiaocun Sun, Kaitlin Moorhead, Thomas Doherty evaluated using the gel intravaginally to determined if it was useful as a sedative when delivered in this manner.

Six adult mares were used in the study. Each mare was studied twice, a week apart. On each occasion, the mare received detomidine intravenously or by applying the gel intravaginally. The team monitored the effects of the drug, including heart rate, ataxia, distance of muzzle to the floor and degree of sedation.

The team determined that the sedation lasted longer and was deeper when the detomidine was given intravaginally; they consider this a viable delivery method in mares. Additional research needs to be done to determine if a mare's heat cycle would affect absorption of the drug.

Read the full study here.