Biology

Camelid evolution began in western North America, 40–50 million years ago. Old World camels (OWCs) crossed the Bering Strait land bridge during a glacial period in the Pleistocene Epoch, approximately three million years ago. Likewise, New World camelids (NWCs) traveled south across the Central American land bridge around the same time. Both OWCs and NWCs continued evolving in harsh, but differing, environments. The two environments had a common characteristic of sparse, poor-quality forage for at least part of the year. See Table 60-1 for additional information.

Camels have been domesticated for 4500 to 5000 years and NWCs up to 7000 years ago. No truly wild dromedary camels, Camelus dromedarius exist, but a sizable population of feral camels exists in the outback of central and Western Australia, a result of escape or purposeful release of camels imported into Australia during the 20th century. A small population (<1000) of wild Bactrian camels, Camelus Bactrianus ferus, exists in the Gobi desert of Mongolia.⁵

Present South American camel (SAC) wild species are the guanaco (Lama guanicoe) and the vicuña (Vicugna vicugna). Domestic species are the llama (Lama glama), and the alpaca (Vicugna pacos). Recent studies on the phylogenetics of SACs on mitochondrial deoxyribonucleic acid (DNA) strongly indicate that the alpaca evolved from the vicuña and the llama from the guanaco.⁶ All camelids share the same number of chromosomes (2n = 74). SACs may interbreed naturally and with artificial insemination, producing fertile offspring. Likewise, camel species also interbreed. Hybrids of a dromedary male and a guanaco female have been produced with artificial insemination.

Unique Anatomy and Physiology

In camelids, a foregut fermentation system and a rumination cycle evolved in parallel with the digestive systems of ruminants. It appears that the common ancestor of both lines had a simple stomach. Camelids have a three-compartment stomach (C-1, C-2, C-3), and the compartments are not analogous to the four compartments of the ruminant.⁵ All of the compartments of the camelid stomach have a glandular epithelium. Numerous other morphologic differences of the digestive system affect the diagnosis, treatment, surgery, and management of diseases in SACs. A greater omental sling is absent. The spiral colon has five coils.

The dental formula for both Bactrian and dromedary camels is incisors (I) 1/3, canines (C) 1/1, premolars (P) 3/2, molars (M) 3/3. The upper incisor has migrated caudally and become caniniform. The first premolars of the upper and lower jaws have migrated rostrally and have also become caniniform. This array of canine teeth (three in each upper jaw and two in each lower jaw), coupled with the unique ability of the camel to open the mouth widely, provides the camel with a formidable tool for offensive and defensive behaviors, so handlers should be continually alert.²

The dental formula for NWCs is I 1/3, C 1/1, P 1-2/1-2, M 3/3. The upper incisor has migrated caudally to become caniniform. The canine teeth of the llama male are large and saber shaped and may be used to inflict lacerations on other male llamas and humans. The incisors of alpacas and vicuñas have an open pulp cavity and continue to grow similarly to rodents.

Camelids have a fiber coat that is harvested and manufactured into garments. The finest fibers, with a diameter of 15 microns, are from the coat of the vicuña. The finest camel fiber is shorn from Bactrian camel yearlings (16–18 microns). The fiber diameter of the alpaca is 21 to 22 microns and llamas, guanacos and adult camels may reach 31 to 35 microns.

Camelids have two digits on each foot (digits 3 and 4), with a nail, not a hoof, at the tip of each digit. The nail is attached to the corium of P3 by means of numerous lamellae. In the SAC, P-2 and P-3 lie in a horizontal plane just dorsal to a tubular fibroelastic digital cushion. In the camel, P-3 is horizontal, but P-2 is at approximately a 35-degree angle with the ground and P-1 is at 55 degrees, when the foot is flat on the ground but not weight bearing. When weight is applied, the angles become more acute as the digital cushion is compressed. In camelids, separate digital cushions for each digit are present ventral to the articulation between P-1 and P-2 and occupying the caudal half of the foot. Each digital cushion consists of a central mass of adipose tissue surrounded by a thick capsule of fibroelastic connective tissue. The digital cushion gives this suborder of artiodactylids the name of Tylopoda (padded foot). The entire ventral surface of the camel foot is covered by a thick, cornified, but pliable sole or slipper. In SACs, the slipper is on each digit.³

Male dromedary camels have a palatine diverticulum (“dulaa”), which is an expandable diverticulum present on the ventral median aspect of the soft palate and which protrudes from the mouth when the animals are angry, agitated, frustrated, in rut, or sexually stimulated. Dulaa is an Arab word meaning “balloon-like structure.” Bactrian camel males and females, as well as dromedary males castrated before or near puberty, do not extrude the dulaa.⁵

Camels are uniquely adapted for dealing with heat and dehydration. Camels are able to endure a diurnal fluctuation of body temperature, from 36.5° C to 42° C (97.7° F to 107.6° F), allowing them to avoid losing moisture through sweating during the day and becoming chilled in the cool desert night. Other species cannot tolerate such a fluctuation. Camels are able to sustain a 25% body weight loss as a result of dehydration without observable ill effects. Furthermore, they are able to rehydrate immediately when given free access to water. The elliptical erythrocyte of camels is able to swell to 240% of normal without rupturing. Other moisture-conserving adaptations include reabsorption of water from the bladder and concentration of urine to a thick syrup consistency before excretion. Also, feces are passed so desiccated that it may be used for fuel immediately.

When other lactating mammalian species are starved and lack sufficient water intake, their milk becomes more concentrated and diminishes in quantity. Even though a camel may be on a poor ration and may be dehydrated, its milk actually becomes less concentrated, allowing camel calves to obtain necessary fluids and be nourished at the same time.

NWCs are adapted to cool weather and are not heat tolerant. Special care must be given them in hot, humid climates to prevent heat stress.

Housing

Camelids may be housed as other domestic livestock species, taking into consideration that dromedaries are adapted to hot desert environments and Bactrian camels are adapted to cool to cold desert environments. NWCs require minimal housing. They should be provided with protection from inclement weather, particularly harsh winds in extremely cold climates; however, these animals are often seen standing or recumbent in rain or snow storms, even when shelter is available.

Guanacos and vicuñas are social animals and generally tolerate close association with others of their own kind. Adult breeding males should not be kept in the same enclosure to avoid fighting among males.

Feeding and Nutrition

OWCs and NWCs have no unique nutrient requirements. They may be maintained on a diet of good-quality grass hay or mixed grass and legume hay. Supplemental feeding with concentrates is usually not necessary except for growing juveniles, working animals, and lactating females. Vitamin and mineral supplements are appropriate for specific regions. Numerous feeding regimens are used worldwide, indicative of the adaptability of these animals to available feed. Camelids consume approximately 1% to 2% of their body weight in dry matter when consuming good-quality forage. A maintenance diet should contain 10% to 14% crude protein and 50% to 55% total digestible nutrients (TDNs). During late gestation or heavy lactation, females should consume 60% to 65% TDNs.⁵

Camelids that eat only native pasture plants may experience fluctuation of body weight. During the dry season animals may lose weight that in other domestic animals could be fatal. NWCs have a feast or famine cycle. With the abundance of grass and shrubs available in the rainy season, an NWC will gain significant weight by storing adipose tissue in muscles and retroperitoneal tissue in the abdomen. During the dry season, NWCs alter their metabolism to use up the stored fat. Management of NWCs maintained in zoos or kept as livestock in non-native countries may not have this normal cycle and may become obese with constant access to feed.

It is important to monitor body weight periodically or perform a body condition evaluation in managed herds. Body condition is assessed by feeling the muscles over the withers and over the ribs. The accumulation of fat between both the forelimbs and hindlimbs should also be taken into consideration. The scoring is performed on the basis of either a 5-point or 10-point system. Low numbers indicate poor condition, medium-range numbers are considered normal, and high numbers indicate overconditioning or obesity.

Restraint

A camelid’s response to restraint varies with its age and stage of life. Camelids have been domesticated for thousands of years and are easily managed if they are accustomed to handling by people. Training has become important in the management of camelids and may obviate some of the following procedures. Improperly trained adult camelids (some zoo camels, privately owned camelids, feral camels) may inflict serious to fatal injuries on an unsuspecting handler. Even well-trained adult males may become belligerent and dangerous while in rut.⁴

Camelid offensive and defensive behaviors include spitting, biting, and kicking. Spitting, which involves spewing the contents of the first compartment of the stomach, is aimed at people or other camelids when the animals become angry or frustrated. Biting may be dangerous, especially when a male camel bites, clamps on, and shakes its head, causing considerable contusions and severe lacerations. In camels, all four feet and legs may become formidable weapons. The front legs may strike out in any direction. The rear legs have the ability to reach forward to the extent of scratching the head. Thus, no place is safe around an untrained camel, compared with, say, a horse (at the side of the withers).

NWCs also spit and kick. Their kick involves a sweep forward and outward, similar to the kick of a bovine species. Other aggressive behaviors include charging and bumping. If a human victim is knocked down, which is most likely to happen, an aggressive camelid may stomp on the person as on another camelid knocked down during a fight. Llamas and alpacas may also bite, but do so rarely.

The degree of psychological restraint that may be employed depends on taming and training. Camelids exhibit emotions by body language, particularly through its ear and tail positions. Ear position is not as apparent in camels as it is in llamas or alpacas because the ears of camels are not as long or as expressive, but they do reflect mood. The farther the ears are pulled toward the rear, the higher is the degree of agitation. The tail of an agitated camelid is elevated. Vocalization is an indication of a camelid’s displeasure. Restraint of even a mild degree is likely to elicit a long, complaining roar in a camel or a scream in an NWC.

It is wise to take advantage of the social behavior of camelids and move them as a group to a smaller enclosure, through the alley way, and to the box stall or catch pen. This is particularly important when handling alpacas.

Positioning a camel in sternal recumbency (“kushing”) provides an opportunity to closely examine or collect specimens for laboratory tests without risk of being kicked or struck. Either a leather strap or rope is used to place a simple or figure-of-8 loop around the front limb when the leg is flexed at the knee (carpus). If only the simple loop is used around the front leg, the camel may be able to rise to its knees. Most camels are trained to allow hindlimb physical restraint, in which a person on either side of the camel brings a soft cotton rope up behind the hindlimbs below the fetlock as the camel is being directed to kush (lie down). Once the camel is recumbent, the rope is placed medial to the stifles and tied tightly over the back behind the hump. Rising on the forelimbs is prevented by placing a loop over a flexed limb, extending the rope over the top of the neck and securing the opposite foreleg in the same manner.

The method of catching a camelid and controlling the head depends on the experience and usual practice of the personnel involved. Camelids may be roped with a lariat, but the roper needs to be highly skilled. A loop may be placed around the neck to pull the head toward a barrier, thus allowing placement of some type of halter.

Numerous types of chutes and stocks have been used to restrain camelids. One design may be constructed next to a barn or solid wall. A heavy post is set approximately 45 centimeters (cm; 1.5 feet) from another post positioned next to the wall. A 2.5-cm (1-inch) thick sheet of marine plywood—1.2 meters m (4 feet) by 2.4 m (8 feet)—is fixed on the post with heavy bolt hinges. Another post may be attached on the inside of one post to narrow the openings in enclosures for smaller camelids. A post set 60 cm (2 feet) in the front of the shoulder posts allows the animal to be tied, thus restricting backward movement. Once the camelid is tethered, the gate(s) may be swung closed, restricting side motion. Bales of hay or straw may be placed behind the camelid if a rectal examination is necessary.

Even the best-designed stock or chute is useless if the camelid will not enter it or cannot be led into it. Placement of the stock or chute in relation to the corral design is the key. If the chute is located in an area that is strange to a camel, or if a camel has not been trained to walk into the chute, handlers will be unable to force an adult camel to enter. Chutes for handling llamas or alpacas are available commercially in a variety of designs.

Chemical Restraint

Generally, it is not necessary to sedate trained camelids for routine diagnostic procedures. When dealing with camels having had little or no taming or training and if chutes or stocks are not available for physical restraint, it may be necessary to administer a tranquilizer or chemical immobilizing agent before procedures. Numerous agents have been administered to camelids for this purpose (Table 60-2). Availability, cost, and experience in using the agent may dictate the choice of agent.⁵

TABLE 60-2

Chemical Restraint Agents Used in Camelids

Generic Name	Trade Name	Dose (milligram per kilogram, intramuscularly [mg/kg, IM])	Reversal Agent/Dose (mg/kg)
Xylazine hydrochloride (HCl)	Rompun1,7	0.1–0.4	Yohimbine (Antagonil8, yobine5) 0.125–0.25 mg/kg Tolazoline HCl (Tolazine5) 0.5–5 mg/kg
Xylazine/butorphanol	Rompun/torbugesic3	0.2/0.05	Tolazoline 0.5–5 mg/kg
Butorphanol tartrate	Torbugesic	0.05–0.1	Naloxone (Narcan8) 0.1–0.25 mg/kg, intravenously (IV), plus 0.04–0.07, subcutaneously (SC)
Diazepam	Valium4	0.05–0.3	Flumazenil (Mazicon4) 1–2 mg/kg, IM
Midazolam HCl	Versed4		Flumazenil
Acepromazine maleate	Promace3	0.05–0.1	None
Propionylpromazine	Combelen1	0.03–0.2	None
Xylazine/ketamine	Rompun/Vetelar3	0.25–0.4/2–3	Tolazoline for xylaxine
Xylazine/ketamine/ butorphanol	Rompun/Vetelar/Torbugesic	0.1/2–3/0.05–0.1	Tolazoline for xylazine
Meditomidine/ Ketamine	Domitor2/Vetelar	0.06–0.08 /2–4	Atipamesole for meditomidine, 4 to 5 times dose of meditomidine, 0.1–0.15 mg/kg, IV, rest SC
Tiletamine/zolazepam	Telazol3/Zoletil	2–3	Flumazenil for zolazepam
Diazepam/ketamine	Valium/Vetelar	0.2–0.3/5–6	Flumazenil for diazepam

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