Road Transport of Late-Pregnant Mares Advances the Onset of Foaling.

The research article discusses how the transportation of late-pregnant mares can accelerate the process of foaling, potentially due to the increase in maternal cortisol, a stress hormone, released during stressful situations such as transport.

Background and Hypothesis

• The researchers based their experiment on the hypothesis that the increase in the release of cortisol, a hormone related to stress, can expedite the onset of foaling, or giving birth in mares. This assumption stems from previous understanding that cortisol has a significant role in initiating parturition, or the process of giving birth.
• Transport is perceived as a stressor for horses, which can induce an increase in cortisol release. Therefore, the researchers aimed to determine the effects of transport-induced stress on the timing of foaling in late-pregnant mares.

Experimental Design and Procedure

• Twelve late-pregnant mares were transported by road for three hours, while four mares were left in their stables as controls.
• The experiment started on the 325th day of gestation. Saliva and blood samples were collected for cortisol and progestin analysis respectively. Additionally, fetomaternal electrocardiograms were recorded regularly.
• The mares were checked for impending parturition and changes in the pH of the precolostrum, a form of milk produced by the mammary glands during late pregnancy. When the pH decreased to 6.5, mares were transported or left untreated based on the experimental design.

Results and Findings

• After birth, saliva was collected from both mother and foal, heart rates were recorded, and foals were checked for health and maturity.
• It was observed that gestation period was 337 days on average in stressed mares and 336 days on average in the controlled mares. Transported mares (identified as stressed) exhibited an increase in cortisol concentrations.
• The study found no differences between the two groups in terms of maternal heart rate, fetal heart rate, and variability in heart rates. Moreover, the duration of foaling, time taken for foals to start standing and suckling, and the postnatal increase in heart rate didn’t differ among the groups.
• However, in transported mares, the time taken from the precolostrum’s pH decrease to the onset of parturition was notably shorter as compared to the control group.

Conclusions

• The findings suggest that the release of cortisol induced by transportation stress potentially advances the onset of foaling in mares.