Chemical Immobilization for Buffalo

Capturing, immobilizing, and fitting for radio collars are common practices in studies of large mammals. However, many species of large mammals exist in remnant or “island-like” populations in which there is little or no gene flow.¹ Concern amongst researchers and conservationists has been raised regarding the potential negative consequences of inbreeding in these species, but important genetic data are scarce as regards many of these populations, since individuals are difficult to handle. The American bison (Bison bison) is the largest native land mammal in the Americas, and a good example of such a genetically isolated species occurring in national parks and refuges in North America.

Although practices attendant to the chemical immobilization of free-ranging and captive wildlife have been well-documented, there are few reports on the use of potent narcotics on either free-ranging or captive bison. Typically, literature on this topic is limited to use of the drug etorphine.²

In North America, many bison live in reserves where restraint is sometimes possible without resorting to the use of narcotics. However, significant natural or reestablished populations of bison still occur, and often it is not possible to capture entire or large segments of these populations in remote areas.¹ This is particularly important when data are necessary for the purpose of conservation.

Wild Bison in North America

Scientists tell us that bison crossed the land bridge that connected the Asian and North American continents thousands of years ago. Over the centuries, they slowly migrated south, eventually reaching as far south as Mexico and as far east as the Atlantic Coast. As we know, the largest herds wound up thriving on the plains from the Rocky Mountains east to the Mississippi River, and from Canada to Texas. Although it is difficult to ascertain with certainty, it is believed that the size of these plains herds numbered 30 to 75 million.

"The moving multitude... darkened the whole plains," wrote Lewis and Clark after they encountered a herd in White River, South Dakota in 1806.

Buffalo can live to be about 20 years of age. Like domestic cattle and sheep, buffalo have cloven hooves, and both the males and females have a single set of hollow, curved horns. The bulls are immense in size, often weighing a ton or more and standing five to six feet high at the shoulders. The head is huge, behind which is a large hump covered with dark brown wooly hair. The females, or cows, are not as massive, at between two thirds to three-quarters the size of the bulls, on average. Despite their great size and bulk however, bison possess amazing speed, and agility, and are able to sprint at speeds of up to 30 mph.³

Sadly, by 1800, the small buffalo herds east of the Mississippi River were gone. Many of these were likely killed to protect livestock and farmlands in these areas. With the westward expansion of the American frontier, the systematic reduction of plains herds began at around 1830, when buffalo hunting became the chief industry of the plains. At that time, many frontiersmen also wanted to eradicate buffalo as a way to take away the livelihood Native Americans, who depended on the buffalo's meat and hides. Many still believe that bison have special spiritual and healing powers, making it an important part of their culture.

The construction of the railroads across the plains further hastened the depletion of buffalo populations. Hunting from train windows was advertised widely, and passengers shot them as the buffalo raced beside the trains. By 1883, both the northern and the southern herds had been destroyed. By the turn of the century, less than 300 wild animals remained in the U.S. and Canada.

Conservation of Wild Buffalo

Conservation of buffalo was only a minor concern in the late 1800s, but became more of a concern in the 20^th Century. In May 1894, Congress enacted a law making buffalo hunting in Yellowstone National Park illegal. In 1902, money was appropriated to purchase 21 buffalo from private herds to help build up the dwindling Yellowstone herd. At that time, there was genuine concern in the U.S. that this majestic animal might indeed become extinct. With increasing protections protection, this herd steadily increased; today the Yellowstone herd numbers over 4,000 animals.

Thousands of buffalo also inhabit the National Bison Range in the Flathead Valley of Montana, the Wichita Mountains National Wildlife Refuge in southwest Oklahoma, the Fort Niobrara National Wildlife Refuge in northern Nebraska, Sully’s Hill National Wildlife Refuge in northwestern North Dakota, and Walnut Creek National Wildlife Refuge in central Iowa. Many other private herds have boosted the buffalo's overall population over the years as well.

In the Spring, the bison begin to shed their heavy winter coats, and with the arrival of the breeding season in mid- to late Summer, the herds become restless. The bulls, who are solitary most of the year, now begin to associate with the cows and calves. The bulls also begin to bellow and become quarrelsome. Many fights occur over females, and the combatants paw the earth defiantly with lowered heads.

Cows give birth usually every year to one calf. Most of the calves are born between the middle of April and end of May, but some arrive as late as October. At birth, the calves have only a faint suggestion of the hump they will develop later.

Chemical Immobilization of Buffalo

Studies of bison movements (individuals and herds) as well as incidence of brucellosis in bison have necessitated that these animals are occasionally restrained so that radio-equipped collars can be attached or blood samples can be drawn. While bison cows and younger bulls are typically easy to drive into corrals for these purposes, the bulls, particularly older ones (averaging around 907 kg or 1 ton in weight), often resist movement to corrals.² For these and other purposes, chemical immobilization and capture is necessary.

For most of the last century, veterinarians and wildlife managers have widely used the narcotic drug etorphine to sedate buffalo. Etorphine is a thebane derivative chemically related to morphine which can be reversed with antagonists cyprenorphine and diprenorphine.¹ The development of more potent narcotic derivatives, such as carfentanil however, has made it possible to utilize much smaller drug volumes and smaller projectile syringes to increase darting efficiency and safety.² Carfentanil is an analogue of the popular synthetic opioid analgesic fentanyl, and is one of the most potent opioids available.

Today, xylazine is often used in the chemical immobilization of bison, as well as combinations of xylazine and carfentanil. Xylazine HCl is a non-narcotic compound that is commonly used as a sedative, analgesic, and as a muscle relaxant. Xylazine has a long-standing use in small animal practices, but it is also used in large animal and wildlife applications. The sedative and analgesic activity of xylazine is related to central nervous system depression. Its muscle relaxant effect is based on inhibition of the intraneural transmission of impulses in the central nervous system.⁴

A widely-used protocol for the chemical immobilization of bison comes from the state of Alaska in the U.S., which routinely engages in this practice:

For the reversal of xylazine/carfentanil formulations, the Alaska Department of Wildlife recommends naltrexone dosed at 100mg/mg of carfentanil used, and tolazoline dosed at 1mg/lb. for reversal of the xylazine component. Both can be injected IM.

Upon achieving sedation, it is reported that bison often go down in lateral recumbency, so it is recommended that capture crews be prepared to get to the animal quickly maneuver it into sternal recumbency in a more natural position. Bison, as well as most members ofthe bovid family, are very susceptible to the effects of the α-2 sedatives such as xylazine, so doses should be carefully measured.

The state of Alaska further reports that their domesticated bison have been successfully handled with the use of tiletamine/zolazepam dosed at 1 -2mg/lb., but attempts to use this formulation to capture wild bison in Alaska have not been successful.

¹Ralls, K. et. al.(1979).Inbreeding and juvenile mortality in small populations of ungulates. Science 206:1101-1103.

²Augen, A. 0., et. al. (1976). Immobilization of adult bull bison with etorphine. Proceedings of the Iowa Academy of Sciences 83:6770.

³Kock MD, Berger J. Chemical immobilization of free-ranging North American bison (Bison bison) in Badlands National Park, South Dakota. J Wildl Dis. 1987 Oct;23(4):625-33.
⁴Khursheed R., et. al. Evaluation of xylazine and ketamine for total intravenous anesthesia in horses, American Journal of Veterinary Research 2005 66:6, 1002-1007.

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