According to a research study by Dr. John Newcombe in the UK, the level of activity around a mare may have some bearing on when foaling takes place.
Gestation length in the mare is notoriously variable. Many horse owners have spent night after unrewarding night watching and waiting for a mare to foal. Mares have an amazing ability to put everything on hold until things suit them.
Dr. John Newcombe in the UK published a report on the time of day that mares foaled.
He compared foaling times at two stables. At one stable (Farm A), the mares were turned out on grass at 7:30 am and brought back in at 2:30 pm. The barn was lighted (to stimulate the nonpregnant mares to start cycling earlier) and mares close to foaling were monitored by closed circuit TV.
Activity in the stable stopped by about 4 pm, and by no later than 5 pm all was quiet.
At the other stable (Farm B), the mares were turned out at 9 am and brought back in between 3 and 6 pm. The lighting and closed circuit TV monitoring were the same as on Farm A.
However, on Farm B, there was a lot of activity until late in the evening, occasionally even after midnight, due to various activities including entertainment of visitors.
On Farm A, 76.6% of the mares foaled between 6 pm and midnight, 12.8% foaled between midnight and 4 am and 10.6% foaled between 4 am and 6 pm.
On Farm B, 33.3% foaled between 6 pm and midnight, 44.4% foaled between midnight and 4 am and 2.8% foaled between 4 am and 6 pm.
Most of the mares on Farm A, where conditions were quiet after 5 pm, foaled before midnight, with a sharp drop off in foaling after midnight.
On Farm B, the peak foaling activity occurred between 11 pm and 4 am, after most people had left.
Since the lighting was left on in both stables all night long and was of similar intensity at both locations, the author concluded that the level of activity was the main reason for the later foaling on Farm B, and that mares prefer to foal in a quiet undisturbed environment.
What does this mean to the horse owner? Mares should be left undisturbed, in a quiet environment, when foaling is near. On the other hand, if for some reason you want to delay the onset of parturition, an increase in activity in the mare’s proximity can sometimes result in a day or so delay in foaling.