Predicting Foaling in Mares: Skin Temperature Fluctuations

You’ve done all the right things during your mare’s pregnancy—satisfied the mare’s nutritional needs while avoiding excessive weight gain, supplemented with omega-3 fatty acids, and arranged for preventive veterinary care. But given the serious complications often associated with dystocia in mares, attendance at foaling is paramount. Being on foal watch, however, can be exhausting.

Any tool that could consistently and reliably predict foaling would be a tremendous asset to the industry. Despite great effort, a satisfactory tool remains elusive. New research indicates, however, that monitoring changes in skin temperature may provide valuable information to help predict foaling but only when used in conjunction with other techniques.^*

Various foaling alert systems are commercially available, each with their own quirks or limitations. Examples of current methods of evaluating readiness for parturition include:

• Waxing of the udder;
• Relaxation of pelvic ligaments;
• Increased vulvar length;
• Evaluation of mammary secretions;
• Identifying behavior changes such as restlessness, signs of abdominal pain, tail switching, and showing the flehmen response;
• Foaling alarm systems based on behavioral changes, pedometer, accelerometer, or electrodes that detect humidity as the mare begins to sweat, or probes that identify lateral recumbency; and
• Transponder units sutured to the vulva that identify when the foal enters the birth canal.

In some farm animal species, an increase in body surface temperature occurs shortly before parturition. To determine if this happens in horses, 56 broodmares were fitted with a commercial, high-precision digital temperature sensor held directly against the skin on the left side of the thorax by a belt. These units were placed on the mares each evening after returning from turnout. Mares were maintained overnight in foaling stalls from day 335 of gestation based on the calculated foaling date.

Data collected from five days prior to foaling until time of foaling were included in data analysis. Skin temperature followed a distinct circadian rhythm, with peak average temperatures of 32.62 °C (90.72 °F) at 7 p.m. and a nadir of 30.69 °C (87.42 °F) at 6 a.m.

“Compared to the steady decline in skin temperature observed in pregnant mares on a nightly basis, a distinct surge in skin temperature began approximately 90 minutes prior to foaling, with a peak increase in skin temperature five minutes before birth,” explained Catherine Whitehouse, M.S., a Kentucky Equine Research nutrition advisor. That increase in skin temperature was statistically significant but still quite subtle.

“These findings support the old wives’ tale in which ‘heating up’ occurs prior to parturition,” Whitehouse said.

The researchers concluded that “this finding could lead to further improvements in tools available for detection of impending parturition. However, skin temperature cannot be used as the only predictive diagnostic of impending parturition in the absence of other parameters.”

Once the foal has all four on the floor, be sure it consumes the mare’s first milk, called colostrum, to ensure passive transfer of immunity.

“Supplementing the broodmare with the long-chain omega-3 fatty acids DHA and EPA during gestation and lactation can transfer the many health benefits of these fatty acids to the foal via the placenta, colostrum, and milk,” Whitehouse said.

^*Müller, A., S. Glüge, B. Vidondo, A. Wrobel, T. Ott, H. Sieme, and D. Burger. 2022. Increase of skin temperature prior to parturition in mares. Theriogenology 190:46-51.