Does Nursing Shape Personality Traits in Foals?

Anyone who has closely observed a field of mares and foals may have noticed that some foals prefer one side of the mare or the other for nursing, while others don’t appear to care which side they approach. In foals that seem to show a strong preference, is it the foal’s choice or the mare’s? Does the chosen nursing position influence the foal’s personality in later life? And can conclusions be applied to all horses in all situations, or are there variances by age, breed, location, or management strategies?

Some of these questions arose because of recent studies suggesting that horses react more quickly and aggressively to perceived dangers seen with the left eye and therefore processed in the right side of the brain. Horses with a more dominant right brain are thought to be more fearful and difficult to handle than horses in which the left side of the brain is dominant. Other studies, however, have concluded that horses with a strong bias for one side or the other of the brain are actually easier to train because they are able to learn difficult tasks more easily than individuals that have little difference in dominance between the sides of the brain.

If foals showed a strong preference for nursing on one side or the other, they might be helping the brain to become more dominant on one side because they would have vision out of only one eye during nursing. If a mare allowed her foal to nurse most often from her right side, this would train the foal to watch for danger using its left eye, and would favor dominance in its right brain. Theoretically, this could lead to a mature horse that showed aggressive and fearful behavior.

To study nursing behavior, researchers from the Czech Republic recorded side preference in a group of 79 foals. The foals were observed for two three-hour sessions every 14 days until the foals were weaned. Results showed that about a third of the foals showed a strong preference, nursing from the same side up to 98% of the time. However, there was no particular bias in this group of foals for the right or left side. The remainder of the foals showed no preference, and mares apparently had little or no influence on which side their foals nursed from.

Babies of many species, including humans, nurse with their eyes closed, especially when they are quite young. Is this true for horses, meaning that the side chosen for nursing has no relation to which eye the foal uses to watch for danger? Does the foal ignore the world around itself while nursing, relying on the mare’s signals to react to a threat? With its head tipped sideways to reach the udder, can the foal see anything out of either eye except grass and the mare’s belly? Further studies of nursing behavior may provide answers to some of these questions.