Study Confirms Euthanasia in Horses is Quick, Humane

Study Confirms Euthanasia in Horses is Quick, Humane

Permitting your veterinarian to humanely euthanize your horse can be heart-breaking, even if you know beyond a doubt you are making the right decision.

Photo: iStock

Permitting your veterinarian to humanely euthanize your horse can be heart-breaking, even if you know beyond a doubt you are making the right decision. But does humane euthanasia really stand up to its name? A team of researchers recently sought to find out.

“Euthanasia is a term used to describe the ending of an animal’s life in a painless and minimally distressful way,” explained Monica Aleman, MVZ Cert., PhD, Dipl. ACVIM (internal medicine and neurology), from the University of California, Davis, William R. Pritchard Veterinary Medical Teaching Hospital.

To provide evidence that brain death in horses occurs quickly following euthanasia, Aleman and colleagues measured physiological parameters (such as heart rate and rhythm), assessed brain stem function (using corneal, palpebral, and pupillary light reflexes and a brainstem auditory evoked response, or BAER), and electrical activity in the heart and the brain’s cerebral cortex in 15 horses scheduled for euthanasia. Loss of electrical activity of the cerebral cortex and BAER are indicators of brain death.

The protocol the study authors used was consistent with how practicing veterinarians perform euthanasias and included placing an intravenous catheter in the jugular vein, administering sedation to relieve anxiety, and rapid administration of the barbiturate pentobarbital sodium (77 to 109 mg/kg, or approximately 100 mL for horses weighing more than 400 kg, or 900 lbs).

The researchers determined that:

  • The average time to inject the pentobarbital sodium was 46.8 seconds;
  • Visible and audible breaths were not detectable by the end of the injection;
  • Electrical activity of the cerebral cortex was lost first, either during administration of the drug or within 52 seconds of when the injection was administered;
  • Brain stem reflexes were lost second to electrical activity of the cerebral cortex, followed quickly by BAER;
  • Within one minute, heart sounds were not audible and an arterial pulse was undetectable;
  • Mean arterial blood pressure was undetectable by 52.6 seconds after the injection; and
  • Electrical activity of the heart was the last to cease; the team believes this is due to the heart using its last reserves of energy, resulting in ineffective contractions (considering there were no detectable heart sounds or arterial pulses).

“These findings confirm that an overdose of pentobarbital sodium administered by rapid intravenous injection is an effective, fast, and humane method of euthanasia, with brain death occurring within 73 to 261 seconds of injection,” Aleman concluded.

This means that owners and veterinarians faced with the difficult task of euthanizing a horse can take comfort in knowing that the procedure is rapid, painless, and minimally distressful for their equine companion.

The study, “Cerebral and brainstem electrophysiologic activity during euthanasia with pentobarbital sodium in horses,” was published in the Journal of Veterinary Internal Medicine

About the Author

Stacey Oke, DVM, MSc

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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