Stress effects on the regulation of parturition in different domestic animal species.

This article reviews the current knowledge on how stress impacts the childbirth process in various domestic animals. The researchers provide insight into the role of stress responses in regulating the onset and progression of childbirth, observing that stress can both prompt and impede labor.

Stress and Onset of Parturition

• The researchers discuss the role of cortisol, a hormone often associated with stress, in initiating childbirth or parturition. Maternal cortisol increases during the before-birth period, helping to trigger parturition. However, there’s an additional increase in cortisol during actual labor, signifying a stress response.
• The final moments of childbirth in most foaling mares and calving cows are characterized by sinus arrhythmias—a variation in heart rhythm—which indicates a state of parasympathetic dominance where rest and conservation of energy are prioritized.

Impact of Environmental Stress on Parturition

• Over the course of the study, the researchers examined the effects of transport stress on pregnant cows and mares. In cows, road transport led to an increase in cortisol levels. However, connection between transport stress and miscarriage remained ambiguous.
• In contrast, transport had a more direct and noticeable impact on mares, causing not only a stress response but also brought forward the time of childbirth.

Stress-triggered Delays in Parturition

• In studies with rats, mice, and pigs, the researchers found that moving animals to a stressful environment after the birth of the first young resulted in a delay in the delivery of the remaining litter. This delay was attributed to an increase in opioidergic tone, which suppressed oxytocin release – the hormone that facilitates childbirth.
• Similar observations were made with mares. When mares were moved to an uncomfortable stable after the rupture of fetal membranes, the time taken for the complete birth of the foal was twice as long. The mechanism delaying the progress was determined to be an increase in sympathetic activity, similar to what was observed in mice.

Postnatal Period and Stress

• The researchers also noted that both equine and bovine neonates exhibited significant stress reactions immediately after birth. This was characterized by high sympathetic activity and an increase in cortisol concentration.

This research sheds light on the complex interplay between stress responses and the process of birth in various animal species, indicating areas for further investigation into stress management during parturition.