11-12-03


Structure and maintenance of the foot in South American Camelids

J. Sue Ault,Veterinary Student
David E Anderson, DVM, MS, DACVS
Head and Associate Professor of Farm Animal Surgery
Director, International Camelid Initiative
Ohio State University
College of Veterinary Medicine
Columbus, Ohio 43210
Phone 614-292-6661
Fax: 614-292-3530
E-mail: Anderson.670@osu.edu



Foot maintenance (e.g. toenail trimming) is vital to longevity and
well-being of South American Camelids (e.g. llama, alpaca) in captivity.
The padded camelid feet are known for being easy on terrain, and their
toenails often wear down on their own when sufficient exercise is
encouraged.  When the toenails of the llamas and alpacas do not wear
down evenly, it is important to trim the nails.  This has importance to
the affects on conformation and long-term joint health.  The foot is an
integral part of the overall stability and locomotion.  A variety of
methods and practices of handling for nail trimming are currently
described.

Foot Anatomy

Camelids and ruminants are both in the order Artiodactyla.   South
American camelids belong within the suborder Tylopoda, Latin for padded
foot.  It is the padded foot that minimizes damage to the terrain and is
ideal for use in hicking and packing activities. There are two digits or
toes on each camelid foot. Congenital defects of the feet are rare.
Three small bones make up the skeleton of the foot.  These are phalanges
one, two and three, referred to as P1, P2, and P3.  The bones P2 and P3
are most distal on the limb and are horizontal to the ground.  The bone
P1 is at a 45-degree angle from upright.  The splayed toes increase
stability and sure-footedness. The thick pad is comparable to that of
most carnivores.

The surface that touches the ground, the plantar surface, is a soft
cornified layer of epithelium.  This is called the sole or slipper.
There is a separate slipper for each digit.  Deep to the slipper is the
corium, a fibrous sheath consisting of connective tissue, containing
blood vessels and nerves.  The digital cushion or "padded foot" of
camelids is interspersed between the slipper, the corium and P2, and P3.
The cushion is made up of collagenous and elastic fibers interspersed
with masses of fat and cartilage. The small non-weight bearing nail is
located at the extremity of the digit, similar to a human nail.  It is
closely attached to P3 via the corium.  The foot is joined to the leg at
the fetlock joint.  The camelid stance is modified digitigrade, similar
to dogs and cats with locomotion on the digits.  Conversely, true
ruminants are unguligrade, walking on the tips of their toes.

The Pacing Gait and Foot Morphology

All camelids have three natural gaits: the walk, the pace and
the gallop.  Camelids are unique among mammals in employment of a
natural pacing gait, a lateral rather than a diagonal gait.  Some
domestic horses and dogs pace, and the giraffe and cheetah employ a
walking pace.  The relatively long-legged SAC's are uniquely adapted to
the pace.  Their legs in the front and rear are set closer to the
midline than in other species and avoid the wasted energy expended in
rocking from side to side at the pace.  However, the animals should not
"single track" and look like they are walking on a tightrope. 

The pacing gait has advantages and disadvantages.  The prime
disadvantage is reduced lateral stability.  The development of the broad
footpad and splayfooted digitigrade stance are considered adaptations to
mitigate this instability.  The camelid feet are digitigrade, modified
from the ruminant unguligrade stance; camelids walk on their digits, or
phalanges, like dogs, instead of the tips of their toes like unguligrade
cattle.  The changes to digitigrade includes the loss of hooves and the
addition of a broad foot pad.  The broad foot pad provides greater
lateral stability during the rolling of the body encountered pacing.

The camelid has other morphological features that would aid in
increasing lateral stability.  Camelids have a narrow chest with broad
flat ribs.  They have enlarged areas of attachment for the muscle groups
that would prevent the body from collapsing towards the unsupported
side.  In order for the animals to walk with their legs under them, they
have a narrow chest and pelvis.  There is no flank on the rear limb, and
this is attached to the pelvis in a small area.  A narrow abdomen allows
free movement of the rear leg.  The column of support of the correctly
aligned leg should be straight in relation to the animal's line of
travel.

It is generally assumed that the foot morphology represents an
adaptation for pacing. Along with this gait, they have a unique foot
morphology or shape.  The camelid foot morphology underwent specific
changes from the ruminant foot.  Specifically, the changes in foot
morphology include splaying of the distal ends of the cannon bones (the
metacarpus and metatarsus proximal to the phalanges), a change in
phalangeal proportions of the first and third phalanx, and increased
motility at the metacarpal/phalangeal joint.

The camelid and ruminants, both artiodactyla, are animals with
paired toes.  The camelid evolved apart from ruminants in very early
geologic time, the Eocene Epoch.  Assuming foot morphology correlates
with the pacing mode of locomotion, paleontology research indicates that
these changes occurred in the Oligocene or early Miocene time. This
preceded the formation of open grassland habitats of late Miocene.  It
is currently speculated at this point that the splayed toe of camelids
gave them additional surface area for supporting weight on soft
substrates like sand.

Leg Conformation

Correct leg conformation from the attachment to the body to the tips of
the toes optimizes bone and joint health throughout the life of the
animal and it therefore is important to its well being.  Numerous
conformation faults detract from balance and inhibit the pacing gait.
This is because the pace is basically an unstable gait with reduced
lateral stability.

A camelid with correct leg conformation has straight legs viewed from
front or back.  A plumb line dropped from the shoulder in front is
observed to drop through the knee and fetlock and between the two toes.
(Figure 2)  Similarly, when a plumb line is dropped from the hip in the
rear the line is observed from the hip through the hock and fetlock and
between the back two toes.  The toes should point forward.   An
indication of normal conformation would be toes that point forward.
Toes that do not point forward may indicate poor conformation or poor
toenail trimming.  In either case, toes that point forward are important
to structurally sound animals. 

Toenail Problems

The toenail in the camelid is non-weight bearing but is
important to tracktion and propulsion.  Many cases of distorted nails
will be seen, some may be corrected, and some may have a permanent
distortion.  Overgrowth of the toenail is the most common disorder of
the camelid foot.  This may provide insufficient wear or curling of the
toenail in which the nail is pushed out of position for normal wear.
The elongated toenails may curve in various directions.  Both toenails
in one foot may curve to one side, both may curve outward or both may
curve inward.

Toenails need to be kept trimmed so toes are in proper
alignment.  This is a conformation fault that detracts from balance and
inhibits the pacing gait.  This is especially important for the health
of the aged camelid such that toe joints will stay in better shape over
time.  A camelid with abnormal foot conformation will have more "wear
and tear" pathology of the bones and joints such as joint pain and
arthritis than when legs are correctly aligned.  Crooked legs, including
the toes, do not provide proper biomechanical support for the animal.

Trimming

Many methods are currently available to assist with the process of
toenail trimming. The primary devices for toenail trimming include rose
or shrub nippers, sheep nail trimmers, a hoof knife, primary shears, or
equine hoof nippers.  Confinement in a chute may aid the process.
Training methods are available based on various handling techniques so
that neither the llama or trainer lose their balance in the process.
The method involves gradual familiarization of the llama or alpaca to
having their legs touched and feet picked up to have their toenails
trimmed.  If necessary, ropes can be placed around the pastern just
below the fetlock.  Also, a convenient time for toenail trimming is when
the animals are being processed and handled for shearing. It is
important to inspect the toenails of all animals in the herd.  The
animals may individually wear their toenails differently.  Several
animals in the herd may wear their toenails evenly, while one animal has
elongated nails.  Additionally, the front and rear toenails of an
individual animal may wear differently.  For example, the front toenails
may have worn properly, but the rear toenails may be elongated and in
need of trimming.  Trimming also varies with the surfaces the animal
utilizes as well as the time of year.

Conclusion

The camelid foot has a broad foot pad with splayed toes.  The
camelid is digitigrade, bearing weight on two phalanges and the third
phalanx at a 45 degree angle.  The camelid is known for its pacing gait.
This gait reduces lateral stability and the camelid has anatomical
developments from their predecessor ruminants to improve stability.
Correct leg conformation is important to long term camelid health.
Legs, including the toes, that do not have proper conformation are
subject to wear and tear pathology.  The toenail in the camelid is
non-weight bearing.  Distorted nails can affect conformation and lateral
stability.  It is important to inspect camelid feet and trim toenails as
appropriate.  Toenail trimming is an integral part of camelid husbandry.









References

Fowler, ME (ed.) Integumentary System, in Medicine and Surgery of the
South American Camelids.
Ames, Iowa State University Press, 1992

Fowler, ME (ed.) Musculoskeletal System, in Medicine and Surgery of the
South American Camelids.
Ames, Iowa State University Press, 1992

McGee, Marty Trimming Toenails in Llama Handling and Training, in
Veterinary Clinics of North
America pp 432, 433

Continuing Education Book, (belongs to Dr. Mattoon) pp. 2.12-2.13

Long, Patrick.  Llama Medicine in Llama Herd Health in Veterinary
Clinics of North America:
Food Animal Practice, pp. 227-231.

Timm, Karen.  The Whys and "What-for" of Leg Conformation in The Alpaca
Registry Journal
Volume III, Number 1 Winter/Spring 1998.

Janis, Christine; Theodor, Jessica; and Boisvert, Bethany.  Evolution of
pacing locomotion in camelids.
in Journal of Vertebrate Paleontology 22(1):110-121.

Fowler, Murray.  Soundness Examinations in Veterinary Clinics of North
America, pp. 23-24.

Myers, Phil.  Camelidae in University of Michigan Museum of Zoology web
page.

Llamapaedia:  Gaits; Toenail Trimming; Toenail Trimming Step by Step

Timm, Karen; Smith, Bradford.  Preparing for the Aged Alpaca in The
Alpaca Registry Journal
Volume V, Number 1, Spring 2000.
 

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