Investigation of the relationship of body temperature, serum estradiol, and serum progesterone to the onset of parturition in the mare

Abstract

In cattle and sheep, a significant decrease in temperature has been noted prior to parturition. In the mare, similar temperature decreases have been documented, although results have been inconsistent when temperatures were taken rectally. One study reported a significant temperature decrease when using data from a radio transmitter inserted into the mare’s flank. The current study utilized nineteen Quarter Horse mares and one Thoroughbred mare, and was conducted from February to June 2006. Each mare had been previously implanted in the nuchal ligament with a microchip capable of reporting body temperatures. Blood collection and temperature recordings began 2 wk prior to each mare’s expected foaling date. Once the mare was estimated to be within 48 h of parturition, temperature was recorded every 3 h until parturition using both the microchip and rectal thermometer. Progesterone and estradiol 17-b were evaluated from daily blood samples from -10 to ± 5 d relative to foaling for determination of the relationship between these steroids and body temperature, time of foaling, birth weight and sex of foal. A significant decrease in rectal temperature (P < 0.05) was noted when the last temperature recorded was taken within 12h of parturition. Microchip data did not demonstrate any significant differences among readings before parturition. No significant difference was noted in the mean rectal temperature of all days relative to the sex of the neonate; however, microchip data showed mares carrying females to have a significantly (P < 0.05) higher mean rectal temperature of all days. Sex of the foal was not shown to be related to maternal concentrations of either progesterone or estradiol 17- b. A direct significant correlation between temperature and maternal plasma concentrations and progesterone and estradiol 17-b was found.