Leg Conformation
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The Whys and "What-for" of
Leg Conformation
Karen I. Timm, DVM, PhDCorrect leg conformation optimizes bone and joint health throughout the life of the animal and therefore is important to its well-being. An alpaca with crooked legs has a much greater chance of developing early "wear-and-tear" pathology of the bones and joints, such as joint pain and arthritis, than one with correctly aligned legs.minimum conformational standards in 1995. As with all of the standards, the objective was to establish functionally relevant, objective criteria. It is important to note that initially the veterinarians used these standards on an "all-or-nothing" basis. For example, the maximum allowable angulation for "knock knees" of the front legs was set at 15 degrees. While many owners would view an animal with a 10-degree angulation as having marginal-to-bad forelegs, it would have passed the vet screening. In contrast, the animal with a 20-degree angulation would have failed.TerminologyFigure 1. Actually, pure anatomists don’t call this a leg since it is technically an arm. It may also be called a front limb or forelimb. The bones, starting at the shoulder and working to the ground, are the scapula, humerus, radius, and ulna; then there are two rows of carpal bones, metacarpals 3 and 4, sesamoids, and phalanges 1, 2, 3 of digits 3 and 4. Alpacas have two "fingers," the third and fourth digits, corresponding to the third and fourth fingers of the human, the middle and ring fingers. • Knock knees, angle greater than 15 degrees ( • Calf knees, angle less than 165 degrees (preferably stated, greater than 195 degrees) ( • Cocked ankle, angle greater than 90 degrees (preferably stated, less than 180 degrees) ( • Down in fetlock or weak pasterns, less than 30 degrees (preferably stated, greater than 240 degrees) (
The alpaca with correct leg conformation has straight legs when viewed from the front or back (Figure 2). In other words, when the front limb is observed, a plumb line should drop straight from the shoulder, through the knee and fetlock, and between the two toes. The toes should point forward. When the hind limb is observed from behind, a plumb line should drop in a similar manner, from the hip through the hock and fetlock and between the back of the two toes. The toes should likewise point forward. When the animal is viewed from the side, the shoulder, elbow, and stifle should have some angulation (Figure 1). The carpal region should be straight (180 degrees) while the fetlock should have an angle of approximately 190 degrees (Figure 3).Figure 4). The "hand" and "foot" is lighter because there are fewer digits. The alpaca retains only digits 3 and 4 on which to walk, compared to the full mammalian complement of five digits.Evaluating Leg ConformationFigure 5). A less commonly occurring defect of the knee is "calf knees," a condition in which the limbs actually bend backward at the knee (Figure 6). The two common defects of the fetlock are weak pasterns and cocked ankle. In weak pasterns, the fetlock sometimes sags so much that it hits the ground when the animal walks. Cocked ankle means that the pastern actually points somewhat backward (Figure 7).Figure 6), and cow hocks, where the hocks point toward the midline (Figure 5). Sickle hocks and cow hocks usually occur together. The extremely post legged animal and the animal with patellar luxations are also considered to have hind-limb defects.
Wear-and-tear pathology is painful, and of course no one wants an animal to be in constant pain from sore joints. But incorrect leg conformation can also decrease the animal’s effective life-span. Animals that find it painful to move will often not eat well and have poorer-quality fiber; males in particular may have decreased fertility. Hind leg problems may prevent a male from breeding because it is too uncomfortable to kush to breed the female. When choosing or evaluating alpacas, certainly features like micron count are important, but leg conformation as close to ideal as possible should be a primary consideration.
The long-term importance of good leg conformation was reflected in ARI’s initial importation screening standards. Based upon input from owners, veterinarians, and other experts in the field, ARI established a set of
The veterinary examination has continued as a "pass-or-reject" system. But in response to owner requests for better overall leg conformation, the minimum standards for imported animals were raised in the phenotypic examination. Consequently, those animals whose legs were somewhat crooked but not badly enough to be rejected by the veterinary exam could fail to qualify through the phenotypic exam.
It is important that veterinarians, owners, and importers start with a similar understanding of what constitutes normal leg conformation, how it is evaluated, and the consequences of skeletal defects.
First let’s review some terminology used in anatomy. Look at the front leg in
Front Limb Rear Limb
The diarthrodial (highly movable) joints of the limb are the combination of the ends of bones, with their cartilage covering, joined to each other by connective tissue of joint capsule and ligaments containing synovial fluid. Ligaments are tough connective tissue bands that run across joints from bone to bone and provide major support for the joints. The joints contain synovial fluid, a viscous, slimy substance that cushions and lubricates the joint.
Muscles and tendons cross the joints so that the pull of muscles changes the angle of the joint. Flexion makes the angle smaller; extension increases it. When you curl your forearm up to your body, for example, you are flexing your elbow, wrist, and finger joints. When you drop your arm to your side the joints are extending.
The joints of the forelimb are the shoulder, elbow, carpal, fetlock, and interphalangeal. The carpus, or knee, is equivalent to the human wrist.
The rear leg (truly a leg) is made up of the os coxae (ilium, ischium, pubis), femur, patella, tibia, and fibula, three rows of tarsal bones, metatarsals 3 and 4, sesamoids, and phalanges 1, 2 and 3 of digits 3 and 4 (toes 3 and 4). The joints of the hind limb are the sacroiliac, hip, stifle, hock, fetlock, and interphalangeal. The stifle is the equivalent of the human knee and the hock the ankle.
Describing the range of angulation is easy if you understand a couple of anatomic precepts. First, angulation of the joints is defined as the range of motion possible during flexion. Thus, the fetlock angle is defined in relation to the metacarpus and the possible range of motion. A line dropped from the tuber ischiadicum should touch the back of the hock, and the metatarsus should be vertical. Normal angulation of the hock should be approximately 140 degrees.
Front Limb Rear Limb
Anyone who has worked with horses and observed their conformation would call alpacas post legged (legs too straight). Alpacas definitely have straighter legs than horses, but they should not have a truly post-legged conformation. Animals that are post legged will have less cushion to their gaits and are prone to patellar and stifle problems.
The legs should also move freely and evenly. They should travel in essentially straight lines with the forward plane of movement. While alpacas have a relatively narrow chest and pelvis and move with their legs underneath them, they should not "single track"—that is, they should not look as if they are walking a tightrope. The distance side to side between foot falls should match the breadth of the individual animal. In other words, the column of support provided by the correctly aligned alpaca leg should be a straight line in relation to the animal’s line of travel.
Alpacas are quadrapedal "cursors" (runners) that move forward in a straight line, designed so that they can travel far or fast on their four legs. Dogs, cats, and horses are also quadrapedal cursors. In general, this group of animals includes predators and medium-to-large-size herbivores.
Camelids are able to move distances as necessary and can run to escape predators. The astounding stamina and speed of young male Patagonian guanacos as they chase each other at continuously high speeds across the landscape are just one example of the camelid’s highly developed cursorial movement. Guanacos are also capable of jumping off of large rock outcroppings, an ability that is also characteristic of quadrapedal cursors.
The basic design of quadrapedal cursors maximizes each stride for speed, endurance, or a combination of the two. The length of the individual stride times the rate of the stride results in speed. Endurance involves speed coupled with economy of effort, which results from a combination of body shape, the ways body parts move, and the mass of body parts. Cursorial animals have relatively longer legs in relation to the body, and the muscle mass is carried closer to the body. Often the distal segment—wrist and hand or ankle and foot—is longer than those of other animals with different functions, and even the portion from elbow to carpus or stifle to hock is relatively longer.
Within the camelids the camels have optimized these features even more than the South American varieties (
Foot posture also contributes to lengthening stride. The bear, a plantigrade animal, walks on the entire hand and foot and has relatively short limbs compared to the alpaca, a digitigrade, which means it walks on nail and pad under part of its toes.
The joints of quadrapedal cursors also allow movement in essentially only the forward-to-backward plane, thereby simplifying motion and conserving energy. To illustrate this point, compare the movement in the human shoulder or wrist to that of the alpaca. The human shoulder and wrist each rotate essentially 360 degrees, while the alpaca shoulder and wrist (carpus) move in one plane.
The best way to evaluate the alpaca’s legs is to observe the animal moving in a calm, relaxed manner, either loose or on a very loose lead. The animal is walked directly away from and toward the examiner and is observed in a side view as well. But theory and reality sometimes clash during evaluations of importations. While the animals are loose, they frequently are nervous. Moreover, most animals do not like to have their legs palpated, making it difficult to evaluate legs in a "hands-on" manner.
The exam can be an entertaining undertaking in a narrow alleyway with curious alpacas on either side of the loose animal. Animals that are scared and tense will often crouch, which results in a sickle- and cow-hocked appearance, so it is very important that the animals are as relaxed as possible.
An animal will pass or fail the importation screening depending on the veterinarian’s observations of the limbs. In the forelimb, defects in alignment most commonly occur in the knee. Knock knees (carpus valgus) are the most common defect. Knock knees are a bending at the carpus toward the midline (
In the hind limb the most common problems are sickle hocks, too much angle to the hock when viewed from the side (
Screening criteria for rejection by the veterinarians include the following:
Forelimb
• Cow hocks, angle greater than 10 degrees toward midline • Sickle hocks, angle less than 125 degrees ( • Fetlock, same as with forelimb (
Hind limb
Other leg conformation faults, recorded as "Other Defects" on the veterinary screening form, may result in rejection of an animal. Most commonly the animals rejected in this category move in an extremely base-narrow manner or have other defects in movement that indicate pathology in joints that are not visible to the veterinarian.
Since the 1996 changes to the screening criteria, leg conformation is also evaluated by the phenotypic screeners. Often there is discussion between the veterinarians and phenotypic screeners to increase consistency in their evaluations.
The phenotypic screeners deduct points for slight and moderate defects. The most common faults noted have been slight-to-moderate sickle hock, slight-to-moderate cow hock, and different gradients of knock knees. Points are also deducted for weak pasterns, a relatively common occurrence. An animal with moderate knock knees and moderate cow and sickle hocks, for example, would lose 21 points and would not be imported.
Always keep in mind that the animals are being evaluated as they are presented and as they appear at the time of evaluation. Later injuries are certainly possible so that animals may exhibit leg problems after importation.
From the veterinarian’s perspective, the ideal animal for evaluation is as naked as a cue ball—there should be no fiber hiding the animal. Unfortunately, this is seldom the case: most animals have moderate-to-heavy coats during the screening evaluation. The quantity and distribution of fiber in particular can make evaluation of the limbs very difficult. It is hard to see the limbs of a suri with fiber dragging the ground. One of the biggest problems this poses is that limbs that are actually straight can appear crooked (
If there are doubts about an animal’s legs, they should be wrapped to compress the fiber. However, it is important not to wrap tightly, to avoid supporting joints that may be weak. In some cases, legs may need to be shorn to be able to truly evaluate an animal.
Though precise angles are specified, evaluation of limbs is not a pure science. It requires the screener to develop over time and through observation of many animals knowledge of what the correct leg conformation of alpacas should be and the skill to identify it.
As with the entire screening process, evaluation of limbs has been an evolving process. The current standards provide a higher minimum bar and have resulted in the importation of more structurally sound animals than was previously the case.
About the Author
Since 1983 Karen I. Timm, DVM, PhD, has taught anatomy and small animal medicine in the College of Veterinary Medicine at Oregon State University and in the last three years has participated in many importation screenings for ARI. She holds a PhD in anatomy and DVM from the University of California, Davis, and has worked as a mixed animal practitioner. She is coauthor, with Brad Smith, DVM, PhD, and Patrick O. Long, DVM, of Llama and Alpaca Neonatal Care.
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