Over the past decade, crib-biting has received much attention from researchers. By understanding this valuable work, we can contribute to the everyday management of crib-biting horses and ponies.
Grasping a solid object between his incisor teeth, the crib-biter will flex the brachiocephalicus muscles (running from his poll to the underside of his neck, sometimes termed the strap muscles) and emit an audible grunting sound.
All equine behaviour, including crib-biting, is controlled by the “supercomputer” — in other words, the brain. In 2018, researchers from the Royal Agricultural University (RAU) and Aberystwyth University revealed some fundamental brain-based differences between crib-biters and “normal” horses. These differences were discovered within two interlinked brain structures which control feelings of pleasure and motivation.
The nucleus accumbens and ventral tegmental area of the brain are naturally activated by the body’s own painkilling and pleasure hormones, known collectively as the endorphins. Crib-biters possess more than double the number of endorphin-binding sites (termed opioid receptors), making the pleasure and motive circuitry hypersensitive and much easier to activate than would be the case for the non-cribbing horse.
In fact, in this sensitised state, the grasping movement associated with the behaviour — which may have originally been directed at finding food — is likely to activate the pleasure circuitry in the same manner as food itself. This explains why crib-biting is so difficult to stop once the behaviour has become part of the horse’s daily routine.
In effect, we are looking at a type of addiction. And in the same way that humans use alcohol and nicotine in stressful situations, it is highly likely that crib-biting helps the horse to cope with the stress often associated with daily management regimes.
The practice of physical prevention with cribbing straps or electrified stable doors could therefore be interfering with a valuable stress-coping tool.
It is worth mentioning that stress seldom contributes positively to training and competition performance. My advice, based upon recent research findings, is not to physically prevent crib-biting but instead to consider alterations to the animal’s management regime.
Feeding the habit?
The opioid receptors display particularly high levels of activation during feeding, especially when the horse is eating a palatable concentrate feed. This is why the highest levels of crib-biting are observed after a feed.
If you are viewing a horse prior to purchase, a small quantity of highly palatable feed will soon reveal crib-biting behaviour. This trick can be useful at horse sales, where the new environment can bring about a temporary cessation in cribbing behaviour.
It is worth considering that the horse’s digestive system has evolved over 50million years to work best with an ad-lib high-forage diet, which is low in carbohydrates such as starch. In fact, cribbing levels in any horse can be significantly lowered if a diet naturally high in forage is provided — and there are some excellent bagged feeds available that feature highly digestible fibre and low levels of starch.
We don’t know for sure what causes these changes within the brain, although work conducted with rodents suggests that changes to the nucleus accumbens and ventral tegmental area are brought about by two factors — namely, stressful life events and genetic predisposition, both of which must be in place for the alterations to occur.
Crib-biting often develops at the time of weaning or after a prolonged period of box rest, as both can be highly stressful to any horse. In a yard of 50 weanlings with identical management regimes, however, only five will ever become crib-biters. This suggests that a horse’s genetic make-up also determines whether or not crib-biting will develop.
At present, there is no genetic test to identify predisposed horses. Lessons learnt from rodents suggest that a proactive coping style, where the animal is always moving and vigilant, goes hand in hand with genetic predisposition towards brain alteration and stereotypy development.
From conversations with owners, this appears to be very much the case in the horse. Should you identify youngsters that are particularly highly strung or hyper-vigilant, my advice is to seriously consider adjusting your management regime to provide prolonged turnout and ad-lib forage to reduce levels of stress.
The bad news, from the rodent research, is that it is very likely that the brain changes are irreversible. We must therefore do our best to prevent them happening in the first place by following the principles of stress-free management.
Busting the myths
Many owners and researchers still link crib-biting to gastric ulcers and suggest that it may be a strategy to alleviate stomach pain.
Recent research by Dr Simon Daniels of the RAU has suggested that a direct link may in fact not exist. Instead, in his paper published in 2019, the findings indicate that both crib-biting and ulcers merely share a causal agent, and that this causal agent is stress.
In support of this idea, crib-biters who also have ulcers remain crib-biters long after the ulcers have healed, so there does not appear to be a direct link. Alleviating the stress helps the ulcers, but due to the addictive nature of the behaviour and the long-term nature of the brain changes, crib-biting will continue.
An additional belief is that crib-biters will “teach” non-cribbing neighbours this unwanted behaviour. As a result, crib-biters can be turned away from livery yards or are isolated from visual contact with others.
In truth, there has been little scientific research directed at this topic. What little work has been completed suggests that stereotypic behaviours, including crib-biting, are not copied in this manner. If we consider stress and genetic predisposition as causal factors, it is unlikely that copying plays a part. Instead, if there is an unusually high proportion of crib-biters in adjoining stables, this is almost certainly due to shared stressors or shared genetics.
At the risk of sounding repetitive, or even stereotypic, the priority should lie in the reduction of stress.
Time for a rethink?
When we looked into learning differences between crib-biters, horses who weaved and a group of stereotypy-free controls, we were surprised by the results. Both the crib-biters and weavers learnt a simple button-pressing behaviour much quicker than the non-stereotypy equivalents.
While pressing a button might not equate to the real-life training scenario, I’ve spent the five years since the findings were published asking owners and trainers what they really think.
At least 90% of the people spoken to find that horses who crib-bite are fast learners and fast thinkers, and do their jobs very well. Since this supports our 2015 findings, it might be time for a rethink. Rather than an unsightly, unwanted “vice”, crib-biting seems to go hand in hand with positive performance attributes. The role of hillwork in fitness
The author: Dr Andrew Hemmings is associate professor of equine science and head of the equine management and science school at the Royal Agricultural University in Gloucestershire. Teaching across a range of equine degree courses, he aims to make the complex topic of neuroscience relevant to horse management. His research interests are centred on the brain and behaviour. rau.ac.uk/equine
Ref Horse & Hound; 5 March 2020