Cribbing and Wood Chewing: Just Gotta Gnaw
- Jul 1, 2002
Cribbing and wood chewing by horses can create problems for horse and owner alike. Wood chewing is often considered by many owners to be a rather benign vice, while cribbing more frequently is considered to be a direct threat to the horse's well-being. However, both can be irritating to the caretaker. There is something unsettling about the repetitive belching sound emitted by cribbers, and the series of U-shaped dips in a board fence created by wood chewers can arouse one's ire.
That's the human side of the equation. What about the horse? Do cribbing and wood chewing compromise his health? There have been some changes in thinking concerning answers to that question as the result of scientific studies.
First, we must differentiate between cribbing and wood chewing.
When a horse cribs, he grasps a hard object with his incisor teeth, arches his neck, and with a grunting-burping-belching sound appears to suck in air through his mouth. Wood chewing, on the other hand, is just that--chewing of wooden objects. The horse simply uses his teeth to gnaw on wood. Often the target is a board fence and, in cases where wire fencing is utilized, it might be wooden fence posts to which the wire is attached.
Cribbing is a fairly common problem. In a 1986 Canadian survey by the Department of Population Medicine at the Ontario Veterinary College at the University of Guelph, of 769 horses at 32 Thoroughbred, Standardbred, and pleasure horse stables in southwestern Ontario, 5.51% of young Thoroughbred racehorses were found to be cribbers. The survey revealed that pleasure horses were close behind with 5.07% being cribbers. Conversely, the Standardbred stables reported no cribbers.
The survey results also revealed that mares were less likely to be cribbers as geldings and stallions, and that the risk of being a cribber increased with age.
For years, horse owners have felt that cribbing was at least potentially deleterious to a horse's health because of the threat of colic from filling the stomach with air, damage to incisors, and the belief that cribbers did not get the maximum benefit from food that was ingested. Cribbing is considered to be such a serious vice that many leading horse auctions, especially those involving Thoroughbreds, publicly identify cribbers as the horse is led into the sales ring.
Almost synonymous with cribbing is wind-sucking, when the horse exhibits the same type of behavior, but does not grasp an object with its incisors.
Wood chewing, on the other hand, has long been considered nothing more than an irritant with little potential for damage to the horse's health unless an inordinate amount of wood is ingested during the process. When that is the case, impaction colic is possible.
Research Clarifies Cribbing
Scientific research has fostered a change in thinking within the equine medical community concerning what actually occurs when a horse cribs. British researchers found that contrary to a long-held belief, very little air makes its way into the stomach when a horse cribs. Thus, doubts were cast on the theory that cribbing is a direct cause of gas colic.
This research was undertaken at the department of clinical veterinary science in 1995 at the University of Bristol in the United Kingdom (UK) and reported in a special supplement to the Equine Veterinary Journal published by the British Equine Veterinary Association.
Reporting on the research was J.G. Lane, BVetMed, FRCVS. "It has widely been stated," Lane wrote, "that horses which exhibit either of these abnormal behavioral patterns (cribbing and wind-sucking) swallow air (aerophagia), and it is also believed that the introduction of large quantities of air into the digestive tract predisposes horses which crib-bite to colic and/or poor bodily condition.
"The purpose of this presentation is to report the results of endoscopic and fluoroscopic studies of the pharyngeal structure of horses during the act of crib-biting/windsucking," he continued. "The major conclusion has been that deglutition (swallowing) does not occur as part of the stereotype and that 'aerophagia' is an inappropriate synonym for this stereotype." (A fluoroscope is an instrument used to observe an internal structure within the body by means of real-time X rays.)
The study involved horses which were known cribbers. The horses stood in stocks for both stages of the investigation and a wooden bar covered with coconut matting was placed at the front of the stocks to provide an inducement to crib.
Videotape recordings were used so that there could be a slow motion analysis of both endoscopic and fluoroscopic images. When the researchers analyzed the data, they were able to follow the sequence of events that occur during cribbing from beginning to end. Researchers' conclusions included the following:
- Swallowing air is not a feature of cribbing/wind-sucking. The events recorded during the stereotypic sequences did not remotely resemble swallowing.
- The source of the characteristic noise associated with this oral stereotypy results from an inrush of air into the upper part of the esophagus.
- Only a small portion of the air that distends the upper esophagus reaches the stomach.
Although the investigators felt that they now understood exactly what happens when a horse cribs or wind-sucks, they didn't know what motivated that particular behavior.
We are left with other questions: Why does the horse seek this "gratification" in the first place? Is it an inherited tendency or is it learned behavior? More about those queries later.
Before we leave Lane and the team of British researchers, another question concerning colic should be addressed--why has there been such a long-standing and accepted association between cribbing and colic?
Lane surmises that the diagnosis was incorrect in the first place. Horses which appear to suffer from colic as the result of cribbing or wind-sucking might actually be suffering from congenital problems in the pharynx involving a lack of muscular development. As the result of an incomplete muscle structure, there can be a continuous column of air making its way from the pharynx to the esophagus and on to the stomach.
"This constitutes true aerophagia," Lane writes, "and the attendants of horses afflicted with this congenital disorder frequently believe they are 'wind-suckers' because of the eructation (belching) noises which they occasionally emit."
Some researchers think horses might wind-suck or crib because of digestive disturbances, possibly because of an imbalance in the pH level of the gut.
Other researchers presented their findings at the first International Congress on Equine Clinical Behavior held in Basel, Switzerland, in June of 1996. Their work also was reported in the Equine Veterinary Journal. They sought to answer other questions involving cribbing and wind-sucking, including finding a solution.
Horse owners through the years have used a variety of approaches to curtail cribbing, all with limited success. These include cribbing straps, elimination of protrusions that the horse could grip, and even surgery.
Sixteen cribbing Thoroughbred geldings were involved in a study at the University of Bristol in the UK. Eight of the horses were fitted with cribbing collars and eight served as controls. The cribbing collars were used for 24 hours, then removed. The collars prevented cribbing in six of the eight horses while they were in place, but when the collars were removed, the six geldings that had been prevented from cribbing by the collars began cribbing at a rate in excess of the controls and in excess of their own baseline (normal) rates, reports Dr. Paul D. McGreevy, a researcher involved with the study.
Surgical techniques have also been used with varying degrees of success. One of the early surgical approaches was developed in the 1920s and was called Forssell's Procedure in honor of the man who developed it. The procedure involved removing a portion of the muscles and some of the nerve structure in the horse's neck that enabled him to arch his neck and flex muscles as part of the cribbing process. The procedure worked in a number of cases, but there was a downside--the technique resulted in disfigurement of the horse.
Through the years, surgeons have worked at refining the technique. The advent of laser surgery has improved the success rate of surgical intervention and has eliminated most cosmetic problems.
Reporting on this approach at the 2001 AAEP convention in San Diego was Daniel J. Burba, DVM, associate professor of equine surgery at Louisiana State University's school of veterinary medicine. Burba said the Forssell technique was modified in laser surgery by making the incisions in a more forward part of the neck. Use of the laser, Burba said, reduced seroma and hematoma (swelling due to localized collections of serum and blood, respectively).
Burba reported that the technique was used on 14 cribbers ranging in age from one to 12 years. Involved were one stallion, five geldings, and eight mares. Eleven were Quarter Horse cutters, and three were racing Thoroughbreds.
Burba presented this succinct report on the results: "None of the horses demonstrated cribbing behavior after surgery. All horses returned to previous function."
Thus, we find, there are methods available to stop the problem, but it is far better to prevent it in the first place than to solve it.
There now is evidence that these repetitive behaviors represent an attempt by the horse to cope with specific stresses imposed on him as a result of his environment and management, noted Daniel Mills, BVSc, MRCVS, principal lecturer in Behavioral Studies and Animal Welfare at the University of Lincoln, UK.
He says that it has been shown that cribbers "tend to suffer from stomach ulcers, and the behavior may be reduced by dietary changes that try to counter the acidity of the stomach.
"It is to be hoped that recommendations focused on changes in diet will soon be able to replace the straps, collars, and surgery used to treat the condition," says Mills. "Not least because these other methods only work by preventing the behavior, but do nothing about addressing the cause."
Regarding stable vices such as cribbing, weaving, and stall walking, researcher M.D. Marsden, of the University of Edinburgh, says that not knowing the cause has led people to try preventing the vices with
mechanical devices, surgery, or aversive techniques (like pepper spray on boards). These approaches might work in the short term, but rarely in the long term.
"The prevalence of a number of myths and their infiltration of the scientific literature regarding causal factors has further hindered progress towards appropriate treatment for horses forming stereotypies," he adds.
"There remain many further details to be elucidated, but 'stable vices' and stereotypic behavior patterns in particular should be regarded as symptomatic not of a 'bad' horse, but of 'bad' husbandry," Marsden states. "Such behavior is the result of housing, feeding, and management practices which are inappropriate to the specific needs of the horse, and it is emphasized that, as in many other aspects of veterinary medicine, careful assessment of causal factors is the key to successful treatment."
What management protocols should be adopted to prevent the development of stable vices, such as cribbing? The German Ministry of Nutrition, Agriculture, and Forestry offers these relevant equine management suggestions:
Exercise--Horses in a free environment spend 16 hours per day searching for food. Under management conditions that restrict exercise, it is essential to find suitable compensation for the loss of activity.
Social Contacts--Horses are social animals. If their demands as social animals are not considered, problems might arise, including behavioral disorders.
Feeding--Composition and quantity of feed must correspond to the individual's requirements for maintenance and performance. A horse's digestive system needs food several times a day for nutrition and time occupation. Frustration from lack of feeding time can result in behavioral disorders. Feeding must take into consideration different demands of performance.
Environment--It is the responsibility of man to offer an environment for the horse that is in accord with the horse's nature and behavior.
So, in order to help avoid stable vices--including cribbing and chewing--and the problems associated with those vices, horse owners should have proactive management practices. Provide sufficient daily exercise and avoid individual or group enclosures that are too small. Supply as much turnout as possible, and keep stabled horses provided with plenty of "munchies" (such as hay), fresh water, and clean air.
Some horses are more difficult to manage, but creating an environment that is healthy for the physical and mental well-being of the horse can possibly alleviate a problem, or keep it from happening in the first place.
About the Author
Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, including Understanding Equine Lameness and Understanding The Young Horse, published by Eclipse Press and available at www.exclusivelyequine.com or by calling 800/582-5604.