New thinking about cribbing
As researchers gain insights into this mysterious behavior, new approaches are emerging for handling horses who crib.
Ccomplaints about horses who crib date back centuries. In one 1889 legal case, a promising colt was returned from Belgium to Scotland on the basis of “unsoundness.” Chief among the complaints: The colt was a “crib-biter.”
This attitude wasn’t unusual: “I have no hesitation in saying that a crib-biter is bona fide an unsound horse…. I verily believe that a crib-biter, sold with a warranty of soundness, is, to all intents and purposes, returnable,” wrote T. B. Johnson in The Sportsman’s Cyclopedia in 1831.
There is no denying that cribbing can be annoying. The horse places his upper teeth firmly on a hard object--be it a fence, stall door, water trough, or anything he can reach---pulls back, arches his neck, and gulps air into the upper part of his esophagus with a distinct grunting sound. What’s more, a cribber can damage walls, fences and other structures around a farm.
Also called wind sucking, cribbing is a stereotypy---a repetitive, compulsive activity that seems to serve no purpose - and it poses some health risks. Horses who crib may be at a higher risk for some types of colic, and prolonged cribbing can wear down a horse’s upper incisors, lead to overdevelopment of particular neck muscles and cause other physical problems. The pressures of cribbing can lead to osteoarthritis of the hyoid, a small bone in the throat. Some cribbers lose weight because they’d rather crib than eat.
Undoubtedly, most owners would like to stop their horses from cribbing. But that is easier said than done. “With stereotypies in general, and cribbing in particular, no matter what people have tried, this is a difficult behavior to effectively stop once a horse becomes habituated to it,” says Carissa Wickens, PhD, extension specialist at the University of Florida. There is no sure-fire cure for cribbing, and the chances of stopping the behavior diminish as the habit becomes more entrenched.
But attitudes toward cribbing have changed since the 19th century, and
even just in the past decades, as research has dispelled several misconceptions about the behavior. For one thing, the behavior is no longer called a “vice.” And the focus of managing a cribber is shifting, from “stop it at all costs” to “reduce the behavior, if possible, or maybe in some cases/in certain situations just let the horse crib.”
Cribbing is no longer an automatic deal breaker when horses are sold, and an increasing number of people are willing to simply tolerate the behavior. “Cribbing can be very challenging to manage, but many of these horses are wonderful animals,” Wickens says. “While we continue to shed light on reasons why horses crib through additional research, we are also striving to encourage horse owners and the wider equine community to realize that the horse is not at fault for stereotypic behavior.”
WHY HORSES CRIB
Researchers still aren’t sure why some horses crib while others managed the same way do not. But most agree that it’s not “contagious”---horses do not adopt this behavior by mimicking others. “There are many non-cribbing horses kept in stalls next to cribbing horses who don’t learn this behavior,” says Amelia S. Munsterman, DVM, PhD, DACVS, DACVECC, of the University of Wisconsin–Madison.
Several surveys have suggested that the tendency to crib may be inherited. In one Japanese survey, for example, the overall rate of cribbing was 1 percent among 1,500 Thoroughbreds but 7 or 8 percent within certain families. In a 2009 survey from Cornell University that included more than 3,500 horses, 162 (4.4 percent) were identified as cribbers with Thoroughbreds found to be at higher risk compared to other breeds---13 percent among Thoroughbreds and 5 percent in warmbloods and Quarter Horses.
It’s possible, though, that the higher cribbing rates seen in certain breeds have more to do with how they tend to be managed than genetics. The current thinking is that an individual horse might have a genetic predisposition to crib, but the behavior isn’t triggered until he is subjected to stressors related to his lifestyle.
“Some things that might lead to cribbing in certain horses include a high-concentrate diet, lack of turnout and lack of socialization with other horses,” says Wickens. “We think horses start cribbing as a coping mechanism. Recent studies have shown that when horses are allowed to perform stereotypic behavior, we see a reduction in the stress hormone cortisol and/or heart rate.”
In a 2016 Swiss study, researchers subjected 19 cribbers and 18 noncribbing control horses to a series of tests that required them to find a bucket of food in an arena. The cribbing horses were divided into two further groups: 10 were permitted to crib during the tests, and nine were prevented from engaging in the activity. Analysis of each horse’s saliva before and after each test showed that cortisol levels were highest among cribbing horses who were not permitted to crib. “Our results suggest that crib-biting horses that did not crib-bite during the learning tests were more stressed than all
The current thinking is that an individual hors might have a genetic predisposition to crib, but the behavior isn’t triggered until he is subjected to stressors related to his lifestyle
other horses,” the researchers wrote.
“This study suggested that cribbing as a coping mechanism might be a valid theory: When the horses were allowed to crib they were less stressed,” Wickens says. However, she adds, not every study has produced the same results: “Other researchers have found no difference at all, and sometimes even a reverse relationship.”
One possible explanation for the discrepancies is the method of sample collection for measurement of cortisol. “In the past we had to do this through blood collection to analyze plasma cortisol. Even if the horse is fairly accustomed to handling and veterinary care, when you draw blood you are still introducing some stress just to get the sample,” Wickens says. “But now that we have less invasive methods of measuring stress hormones [such as in saliva or feces] potential stress induced during sampling is minimized, and the results are often more robust.”
One older theory held that horses crib to release endorphins, which produce euphoria often described as a “high,” but more recent research suggests that the equation is not that simple. “Now, we don’t necessarily think they are cribbing to get the high, but perhaps to relieve stress. The brain chemistry and physiology of cribbing horses is already a little different or becomes altered, and they tend to be more sensitive. So when they are fed a highly palatable meal, it tends to stimulate pleasure receptors in the brain to a degree that is heightened compared to a normal horse,” she explains. “They crib not so much to get the high---they are getting the endorphin release from something else that’s occurring, like the grain meal, and then that influences the behavior or reinforces it. Cribbing is definitely linked to endorphins and opioid stimulation, but it may be that the receptors in their brain are already more sensitive. Different stimuli that elicit that ‘feel good’ response are reinforcing the cribbing, but I don’t think it’s necessarily the cribbing itself that is giving the horse the fix.”
CRIBBING AND ColIC RIsK
Researchers are also still working to understand how cribbing might affect a horse’s health. Horses who crib do seem to be more prone to certain types of colic, although the connection is unclear.
“So far the data we have is limited and does not necessarily point to a true cause and effect,” says Wickens. “We don’t really know if cribbing makes horses more prone to colic or if these
There is still much we do not understand about the relationship between colic and other gastrointestinal problems and cribbing in horses
horses already have some underlying digestive system dysfunction and are prone to colic, and this made them more likely to crib. It’s like the question about which came first, the chicken or the egg. We don’t really know.”
A horse does lift his rib cage and tighten his diaphragm and abdominal musculature when he cribs. “In one study we looked at pressure in the abdomen, and cribbers have higher pressure when they crib, which is not good,” says Munsterman. But the effects of this are not well understood, she adds: “We were unable to actually link this with specific diseases it might cause, but there might be a correlation. We are still trying to figure out if this is something we should pursue in further studies.”
In 2004, researchers confirmed that horses who crib may be more likely to develop epiploic foramen entrapment (EFE) a type of colic that occurs when a section of small intestine becomes trapped between the liver and the pancreas. Of 419 horses who were treated for EFE, 47 percent were cribbers--but it is also important to note that the majority of the horses in the study, 53 percent, developed the condition with no history of cribbing.
“There is a natural hole in the abdomen, called the epiploic foramen, that every species has, including humans,” says Munsterman. “The thinking is that this hole widens in cribbers because of the pressure changes, and at some point a loop of small intestine may slip through, which strangulates that piece. But to actually see it happen, you’d have to open the abdomen.”
Understanding the connections, if any, between colic and cribbing will require further research. “A few studies in the veterinary literature have demonstrated an association between colic and cribbing, but there are many other causes of colic,” says Wickens. “Anecdotally, I have known many cribbing horses who have never had problems with colic and many non-cribbers who have had frequent bouts of colic. There is still much we do not understand about the relationship between colic and other gastrointestinal problems and cribbing in horses, and this warrants further investigation.”
MANAGING TO DISCOURAGE CRIBBING
The thinking that cribbing relieves stress is worth considering when deciding how best to manage a horse who engages in this behavior. “My advice is to not try to stop them, because thwarting this behavior may be cruel,” says Munsterman. “We need to learn more about cribbing because it may be better for the horse to be able to continue this stress-relieving activity, and just figure out a way for him to do it safely.”
Horses who have been cribbing for many years are unlikely to stop, but it is possible that managing a horse to reduce the stress in his lifestyle may diminish the behavior. Here are some things to try:
• Address any underlying discomfort. Some horses may begin cribbing to relieve gastric discomfort. “Abnormal oral behaviors are often associated with gut discomfort, which may stem from feeding management. This might be something to try with the horse that’s just begun to crib and might be successful in halting it,” says Wickens.
“If it’s a younger horse or one that has just started cribbing, you might want to evaluate the diet,” she adds. “If you catch this behavior early, before it has become well established, you might work with your veterinarian to make sure there’s no gastrointestinal issue. It might be easier to redirect a beginning cribber than a horse that’s
Horses who have been cribbing for many years are unlikely to stop, but it is possible that reducing the stress in a horse’s lifestyle may diminish the behavior.
been doing it for several years.”
Many horses who crib have ulcers--although this is not a definitive cause, since many other horses who have ulcers do not crib. While working toward her PhD, says Wickens, “We tested the hypothesis that cribbers have a greater number and/or severity of gastric ulcers [than did horses who do not crib]. When we video-endoscoped those horses, we did not find a significant difference between the non-cribbers and the cribbers in the condition of their stomachs.”
Still, it may be worthwhile to take steps to relieve any potential gastric discomfort. “Keeping [horses who crib] on feeds that help reduce or prevent ulcers is recommended,” says Munsterman. One choice would be to offer alfalfa hay because it is high in calcium and has a buffering effect on stomach acid.
• Feed wisely. Whatever other measures you might take, keeping hay in front of a horse is a good way to keep his mouth occupied. “This is another way for the horse to express his oral fixation, by continually nibbling hay,” Wickens says. “It may not stop the cribbing but might reduce the frequency of it.”
If a horse needs to have his calories restricted, then a slow feeder---which limits the amount of hay a horse can get in one bite---can help to make his ration last longer. Wickens suggests that taking a more creative approach may also help keep the horse occupied: “Rather than just putting some hay out, you might make some effort to enrich the horse’s foraging experience. You might place a few flakes in different areas around the paddock so the horse has to move around and mimic foraging behavior,” she says.
She also suggests offering different types of hay around the turnout. “Some of it could be a little more nutritious if it’s a performance horse or any horse that needs more calories,” she says. “Some legume hay along with the grass hay flakes placed here and there around the paddock or pasture can make a little more work and activity for the horse.” This gives the horse more to do than simply standing at a feeder, eating.
When a horse needs more calories than he can get from forage alone, Wickens recommends choosing feeds with more fat and fiber and less starch and sugar. “In general, this also tends to have a calming effect,” she says. “There are many commercial feeds that contain highly digestible fiber sources like beet pulp and alfalfa meal. These can provide more calories and help maintain body condition while promoting positive behavior and reducing unwanted behaviors.”
Another tactic might be to feed hay first, then offer grain. “A strategy that has met with some success is to make sure they’ve already had some forage before being fed a grain meal,” says Wickens. “If you leave some hay in the stall at the same time you are giving the grain, it may also help. It won’t stop the cribbing but may be a management tool that could help.”
• Maximize turnout and amenable companionship. Horses who begin cribbing are often the ones who, at one point in their lives, were confined to stalls and trained for performance careers. Once the habit is ingrained, many horses will continue to crib even when turned out to pasture with a herd.
“Some owners just don’t have access to pasture for their horses,” Munsterman says. Still, maximizing whatever turnout is available, with amenable companions, may help to reduce the behavior. “If they are out at pasture and doing jobs and a moderate amount of work, there is less time for them to crib,” Munsterman adds. “We are pretty sure the cribber isn’t going to teach the others to crib, so putting him with
Whatever other measures you might take, keeping hay in front of a horse is a good way to keep his mouth occupied.
Mayhew’s Illustrated Horse Management, by Edward Mayhew, 1860