Many
horses are kept in an unnatural environment--confined in stalls
or small pens. Some of them resort to repetitive behaviors such
as cribbing, weaving, or stall walking. Most of these horses are
fed concentrated, high-energy rations they consume quickly,
leaving them with lots of energy, but little to do. Horses
raised on pasture, grazing continually on high-fiber, low-energy
feed, are less likely to develop these habits.
Cribbing is an activity in
which a horse grips a horizontal surface such as a rail, fence,
or stall manger (in earlier years called a crib, thus the name
of the problem) with the top incisors. The horse anchors his top
teeth over the object or presses them into the wood, letting the
lower jaw hang slack. He then flexes his neck, opens his throat,
pulls back with his mouth open, and swallows air with a grunting
sound.
The cribbing horse wears down
his top incisors (the teeth often become so worn the top and
bottom incisors do not meet when the mouth is closed), and he
develops unsightly large muscles under the neck. This can
interfere with proper head flexion when ridden.
Serious cribbers can lose
weight; they become so addicted to their habit they prefer to
crib than eat. Destruction of facilities is a frustration to
horse owners. Once the habit starts, many horses keep
cribbing--even if given access to pasture and grass. They kill
trees, damage fences, and destroy stall dividers and feed boxes.
Prevention vs. Cure
Bonnie Beaver, DVM, Dipl.
ACVB, of Texas A&M University, says it is much harder to stop
cribbing than to prevent it in the first place. "People keep
horses confined and forget they have certain needs," she says.
"High-quality feed creates a high energy level, yet at the same
time these horses must stand in a stall. When a horse has that
much energy, he's going to do something to get rid of
it--walking in circles, weaving (constantly shifting weight from
one front leg to the other), or cribbing.
"Some horses, as they become
nervous, are more mouth oriented than others," Beaver continues.
"Some will lick, or flip water, but many will bite on whatever
is handy."
Simple wood chewing can
progress to cribbing if horses are continually confined. The
more they do it, the more they are programming the brain to do
it. At that point, they want to continue doing it, even when you
get them out of the confinement.
"If you turn them out in a
pasture some may stop cribbing, but if you stress them again,
that's the first thing they do," she says. "And some won't stop;
out in the pasture they'll put their mouth on a fence plank or
any other solid surface and stand there and suck air."
Beaver recommends that if a
horse is confined, find ways to enrich the environment so he
won't start an unwanted behavior. Let him spend half of each day
outside, even if it's at night. "Horses need room to graze, run,
and interact with other horses, even if it's only across the
fence," advises Beaver. "Social interaction relieves the stress
of confinement. They need daily exercise to help get rid of
extra energy, and a change in diet so it's not so high in
energy." Instead of alfalfa hay, feed timothy, coastal, or some
other type of grass hay, and cut down or eliminate the grain.
"Horses tend to pick up
unwanted behaviors when they are young because youngsters have
high energy levels," says Beaver. "Certain bloodlines are more
prone to develop problems. Hot-house horses, raised in stalls
and blankets, under lights, etc., are apt to start cribbing
early."
It's been thought that horses
pick up the habit by mimicking others, but this is difficult to
prove; they might pick it up just because they are in the same
unnatural environment, she says.
If the horse must be in a
stall, give him something to do. Toys (big balls or plastic jugs
to play with) or a companion animal might help. "The best
alternative is to get horses outside where they can move
around," says Beaver. "In a paddock, you can spread hay out in
small piles so they can go from one to another, similar to
grazing activity.
"Working with the horse daily
is helpful, giving him something to think about so he won't be
bored," she says. "Riding in different environments, or being
ponied if the horse is too young to ride, gets him out and
looking at other things. I can't overemphasize the importance of
prevention. The horse has an active mind and we need to keep it
busy."
Attempts to Halt Cribbing
Horse owners have tried many
ways to halt cribbing activity, such as covering stall surfaces
with rounded metal edges a horse can't grab on to crib, shock
collars, and cribbing straps. The latter are fastened around the
throatlatch and adjusted to cause discomfort when the horse
cribs--making it painful to tense the muscles that retract the
larynx. Many straps are fitted with a heart-shaped piece of
metal or stiff leather under the throatlatch. When the horse
arches his neck to suck in air, the strap tightens and the point
of the metal piece jabs him--making him put his head forward
again so he can't swallow air.
The strap is not a solution;
the horse will resume cribbing whenever it is removed. It is
also a nuisance, as it can rub out the mane, wear hair off the
throatlatch, or create sores. Wearing the strap all the time can
also pose risk to the horse if it ever catches on anything.
"Once a horse's brain is hard-wired to crib, these attempts to
halt cribbing won't work," explains Beaver. "You are treating
the symptom and not the cause.
"With a shock collar, for
instance, you are punishing the behavior, but not giving the
horse an alternative, and he doesn't know why he's being
punished," she says. "If you got zapped every time you coughed,
you might try to hold it in, but you still have to cough. The
punishment is not addressing whatever is making you cough."
Surgery to remove various
portions of the three major neck muscles (on the underside of
the neck) used in cribbing is sometimes done to keep a horse
from arching the neck to draw in air, with a neurectomy to
remove a small portion of the nerve on both sides of the neck
that supplies the largest of the muscles. Some owners choose
this option for a confirmed cribber that can't be halted using
traditional methods, but it doesn't always work.
Surgery for Cribbers
Surgery, until recently, was
successful in only 60% of cases, and it sometimes left a horse
disfigured. Some horses eventually began cribbing again even if
they halted for a time, with the horse recruiting other muscles
to participate in the action. Neurectomy worked best if done
when the habit was just starting. Newer surgery methods,
however, have made this a more successful option.
Daniel J. Burba, DVM, Dipl.
ACVS, professor of equine surgery at Louisiana State University
Equine Health Studies Program, uses laser surgery for cribbers.
This method gives a higher success rate because it is performed
on the muscles in a more forward location--decreasing the
possibility of the transected muscle ends growing back together
(a problem that sometimes made earlier surgeries a temporary
solution).
This new technique is a
revision of the modified Forssell's procedure, developed several
years ago. Burba says, "Dr. Forssell originally developed a
method where the ‘strap muscles'--the paired muscles under the
throat (sternothyroideus, sternohyoideus, omohyoideus, and
sternomandibularis)--were transected. A section was taken out of
all those muscles.
"Forssell later revised the
technique because of the unsightly effect it created," continues
Burba. "Instead of cutting the sternomandibularis on each side
of the neck, he transected the motor nerve to those muscles.
This procedure has been used for a number of years, but with
only a 75-80% success rate."
Some of the horses went back
to cribbing because the two ends of the muscles eventually
reconnected with development of fibrosis. "So we went a step
further and did two things," he says. "We take out more muscle;
our transection is more forward, under the jaws, right at the
hyoid apparatus, rather than over the throat area. Also we take
out a 34-centimeter section that includes all three pairs of
muscles and transect the motor nerve (the spinal accessory
nerve) on each side of the neck."
The incision is made between
the jaws and goes a third of the way down the neck.
"We use a laser to transect
these muscles and nerves," he adds. "This reduces bleeding. The
cosmetic aspect is also much better; the horse has a much
cleaner throatlatch area. A lot of horses develop very thick
muscles in the throatlatch area from the cribbing activity, and
this is resolved--there's no longer a thick muscle under there,
obviously."
Burba said they first started
using the laser for these surgeries in 1994. "So far, we have
done nearly 60 surgeries and have kept track of the horses
afterward," he says. "Right now we are running at about a 91%
success rate; very few of the horses have returned to cribbing.
We feel the reason for this success is the more forward
transection of the muscle, creating a greater gap so muscle ends
cannot fibrose back together. Using a laser, which reduces the
post-operative bleeding, also helps.
"Bleeding can lead to a clot,
which can end up as a fibrous tissue," he adds.
The surgeons now do more
closure in the dead space that occurs when they take the muscle
out. They draw the muscles that aren't removed from the
underside of the neck closer together and suture them down. That
helps reduce serum buildup and drainage.
"We still use a drain--put in
at the time of surgery and left in for about five days," he
says. "We use an active drainage system rather than one that
relies on gravity. The tube within the tissue has holes in it to
collect the serum, and a tube coming from it has a suction bulb
on the end. Thus we can keep negative pressure on it. We try to
pull as much of that serum out as we can, and this reduces the
amount of swelling."
Burba has performed the
procedure on horses from yearlings up to 12-years-old. The
average age has been about five years old, with an equal number
of males versus females. "Of the 60 horses we've done, 36 have
been Quarter Horses, because they represent the majority of the
horse population here," says Burba, with the rest being
Thoroughbreds, Warmbloods, Saddlebreds, and Morgans.
"Cribbing is a habitual
action, and we have not changed the mental aspect (the horse
would still crib if he could)," explains Burba. "We just take
the physical aspect away." The horse is no longer physically
able to perform the action since he doesn't have the muscular
structure to keep doing it. The horse probably tries, but can't
do it, and after a while he resigns himself to not doing it,
notes Burba.
"There is no effect on the
horse's performance, head and neck flexion, etc.," following the
surgery, says Burba. "He just can't get into position to crib."
The laser surgery holds more
promise as a "cure" than other methods and is a more permanent
solution. "It is a little involved because of the amount of
muscle we are taking out, so we usually keep the horse here a
few days in our hospital," says Burba. "We keep the drain in for
four or five days, pull it out, and at that time usually send
the horse home. Once the skin is healed after staples are taken
out (about two weeks), the horse can resume training."
Take-Home Message
It is better--and easier--to
prevent a horse from starting the habit of cribbing than it is
to stop that habit. Prevention includes giving horses room to
move around or regular exercise, distractions if they must be
stall-bound, and feeding regimens that reduce the amount of
energy in the diet. There are no cures that work 100% of the
time, although the new option of laser surgery might give
chronic cribbers a second chance if their fate with their
current owner depends on them not cribbing.
Horse
Behavior--Endorphin Addiction
Rhythmic actions (such as
weaving, stall walking, and cribbing) performed by a confined
animal develop in response to stress and are a type of
obsessive-compulsive behavior that is difficult to halt. When a
horse develops a compulsion, it's a clue that his needs for
social interaction, security, mobility, natural feeding
behavior, etc., are not being met. Once established, however,
the behavior becomes a need in itself, and the horse insists on
continuing it.
Twenty years ago, scientists
at Tufts University led by Nicholas Dodman, BVMA, MRCVS, DVA,
MAPBC, Dipl. ACVA ACVB, discovered why horses crib and why the
habit is so persistent. Whenever an animal or human is stressed
and engages in some type of repetitive activity as an outlet for
pent-up energy, morphine-like proteins called endorphins are
released in the brain. The constant activity triggers the
endorphin release. The animal will keep up the habit even when
no longer confined or stressed because he finds that repeating
the pattern produces these calming "opiods" that suppress pain
and create a pleasurable sensation.
Horses seem relaxed after a
cribbing session. As the act of cribbing causes a temporary
sedating effect, the horse becomes addicted to his internal
chemicals. He craves the endorphins and gets his "fix" by
performing the repetitive behavior. Some horses will actually
stop eating and crib during the middle of a meal. This behavior
is truly an addiction rather than just a "bad habit."
