Mares seem to be totally relaxed when giving birth, say Austrian researchers who closely investigated the arrival of 17 foals.
Newborn foals may weigh 20 times that of a newborn human, but that doesn’t necessarily mean they share the same pain and stress that accompanies human childbirth.
In fact, researcher Christina Nagel and her colleagues said the evidence suggested that mares giving birth had the opposite of a stress response, and appeared totally at ease.
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 much shorter than giving birth in humans or cows.
Nagel and her colleagues closely observed 17 foalings at the Brandenburg State Stud in Neustadt, Germany, as well as recording 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.
“Normal foaling appears to cause just the opposite of a stress response,” Nagel said.
Surprisingly, 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 horses 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.
Its antagonist, the sympathetic nervous system, would prepare the organism for a stress response but does not seem to be active while the animals are giving birth.
The level of stress hormones remains low in foaling mares and the researchers did not find an adrenaline rush at any point.
Foaling, they said, clearly did not evoke a stress response.
The need to care for the newborn foal was also not perceived as stressful: contact between the mare and the foal was associated with a further state of relief and relaxation.
Horses therefore 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.
The head of the research group, Christine Aurich, explained: “Parturition in horses requires a state of relaxation in the mare.
“This is an advantage in wild horses because mares can postpone labour until they perceive the environment as calm and safe. Once this is the case, foaling proceeds within a very short time.”
The findings of the research have been published in the journal, Journal Theriogenology.
The study was conducted at the Graf Lehndorff Institute for Equine Science, a joint research unit of the University of Veterinary Medicine, Vienna, and the Brandenburg State Stud at Neustadt, Germany.
“Parturition in horses is dominated by parasympathetic activity of the autonomous nervous system”, by Christina Nagel, Regina Erber, Natascha Ille, Mareike von Lewinski, Jörg Aurich, Erich Möstl and Christine Aurich, has just been published in the scientific journal Theriogenology. http://dx.doi.org/10.1016/j.theriogenology.2014.03.015