Licking and Chewing – Submission or Stress?

Horses sometimes lick and chew during training and this has often been interpreted as a sign that the horse is learning or showing “submission” to the trainer. However, a new study suggests that this non-nutritive licking and chewing behaviour is a natural behaviour that is shown after a stressful situation.

To gain insight into the function of licking and non-nutritive chewing behaviour in horses, a team of equine scientists from the Norwegian University of Life Sciences observed the social behaviour of feral horses under natural conditions.

M.Sc. Margrete Lie and Prof. Ruth Newberry spent 80 hours observing feral horse herds in Ecuador and collected data on 202 sequences of behaviour when licking and chewing behaviour occurred. Margrete Lie presented her findings at the 14th International Society of Equitation Science (ISES) conference in Rome in 2018.

The team wanted to investigate whether non-nutritive chewing was performed to signal submission to another horse, and also to study whether horses performed the behaviour in between stressed and calm situations.

To find out whether non-nutritive chewing was performed to signal submission, the researchers tested the idea that when one horse (the aggressor) approached another horse (the recipient) in a threatening manner, the recipient but not the aggressor would perform the behaviour. The team observed and recorded different behavioural sequences that involved aggressive interactions (for example, if one horse herded or threatened another), and recorded whether the chewing behaviour was performed by either horse.

The results were fascinating. The team found that the chewing behaviour was performed by both the approaching and the recipient horses. Non-nutritive chewing was actually performed more often by the aggressor than the recipient, refuting the assumption this behaviour is a submissive signal.

The researchers also investigated whether non-nutritive chewing occurred between tense and relaxed situations. When observing the horses’ behavioural sequences,