In humans, giving birth is both stressful and painful for the mother. But that is not the case with mares.
Scientists at University of Veterinary Medicine in Vienna have investigated the stress associated with birth in mares and other domestic animals.
The findings show that contrary to expectations, mares appear to be completely relaxed when foaling.
"Normal foaling appears to cause just the opposite of a stress response," said lead researcher Christina Nagel.
Foaling in horses is extremely fast. Labour and the active part of foaling, resulting in delivery of the foal, take 10 to 20 minutes and are considerably shorter than giving birth in humans or in cows.
Is this brief period stressful for the animals or are mares more relaxed than humans when giving birth?
The researchers closely observed 17 foalings at the Brandenburg State Stud in Neustadt (Dosse), Germany, as well as recorded electrocardiograms before, during and after foaling.
The researchers also took samples of saliva and blood and analysed the levels of stress hormones such as cortisol and epinephrine.
During labour, the heart rate of mares does not increase.
On the contrary, the mares even miss some individual heart beats due to delayed stimulus conduction in the heart.
In humans, such second-degree atriventricular (AV) blocks often require medical treatment but many healthy mares show AV blocks at rest.
On physical activity, such as when the horse is ridden, the heart beat becomes regular and the beat frequency increases.
The finding of AV blocks during foaling suggests that mares are strongly influenced by the parasympathetic nervous system, which usually causes a state of rest and relaxation.
The level of stress hormones remains low in foaling mares and the researchers did not find an adrenaline rush at any point.
Foaling clearly does not evoke a stress response.
"Horses thus experience giving birth very differently from human mothers. They need a safe environment to give birth: all the foals in the study were born at night, when the stable was quiet," researchers added in a study published in the journal Theriogenology.