According to a recent study by the Royal Agricultural College in the UK, feeding regimes and modern diets play a significant part in encouraging stereotypies such as crib-biting. Researchers analysed a small population of crib-biting horses during the daytime while they were inactive (not at feeding time). The horses performed 11 incidences of crib-biting every 5 minutes on average. When provided with a palatable concentrate feed this rate increased to 24 counts and lasted for around 40 minutes. However, when the horses were fed a forage meal instead of concentrates, cribbing levels were reduced to 5 incidences and the reduction lasted for at least 50 minutes before increasing back to their usual level (of 11).
So why did this happen? What does it mean and what can we learn from it? In the same way that those of us with a sweet tooth recognise the addictive properties of food like chocolate, which tastes good, is easy to eat and so is highly palatable, researchers recognise that certain feeds have the same effect on horses. Feeding infrequent meals of highly palatable concentrate feed is likely to induce undesirable stereotypic behaviour in some horses. In humans, highly palatable feeds have been linked to the release of pleasure hormones (endorphins) in the brain and it is likely that the equine central nervous system responds in a similar way.
Previous research has implied that crib-biting occurs partly due to stress-induced increases in endorphin sensitivity. Once crib-biting behaviour has developed these endorphin releases can lead to extended bouts of this behaviour. Crib-biters have been found to have around twice the normal number of endorphin receptors in the brain, which means that when they eat a palatable feed, such as a molassed mix, the endorphins released during ingestion can bind more easily with the receptors, inducing a crib-biting response.
The digestive process can also influence behaviour. Concentrate feeds are often rich in starch, which is broken down by intestinal enzymes and converted to glucose. This increases glucose levels in the blood around 2 hours after feeding. It is this glucose ‘boost’ that has been linked with excitable behaviour.
Evolutionarily, horses are not designed to deal with palatable, carbohydrate-rich feed as they are poorly equipped for digesting starch. Our domestic horses’ ancestors lived in tropical rainforests 50 million years ago. They were accustomed to palatable, nutrient-rich feeds such as berries and soft shoots. As this type of diet would have been high in nutrients it is likely that these horses derived sufficient sustenance from a few discreet meals a day rather than constant foraging. Gradual deforestation over the millennia has shaped the modern horse’s reliance on low-palatability grasses associated with tundra and steppe regions of the globe. Such a low-nutrient diet means that modern horses need to graze for up to 18 hours each day in order to gain sufficient nutrients. Domestic feeding regimes that feature one or two meals per day of nutrient-dense, palatable feed may be more suited to their distant relatives than the modern equine athlete.
The addictive effect of endorphins, restrictive nature of the stable environment, along with cues that signal the arrival of food (such as the rattling of feed bins and buckets) are often associated with heightened frustration that leads to anticipatory behaviour such as door banging as well as stereotypies such as weaving and box-walking prior to meal delivery.
If feeding grain-rich concentrates is necessary due to the energy requirements of the high-performing athlete, calming supplements such as magnesium are worth considering as this has been shown to reduce heart rate (do check with your vet though that this doesn’t contravene prohibited substance regulations for the competition horse). Slow-release delivery systems such as a ‘feed ball’ may also offer a solution. There are also automatic feeding systems on the market that regulate the delivery of concentrate feed by releasing a small quantity according to a timed delivery or when the horse activates a button. The latter enables feed-seeking behaviour similar to grazing to be replicated, satisfying the psychological motivation to feed as well as physical hunger.