Assessment of pregnancy in the late-gestation mare using digital infrared thermography

The objective of this study was to investigate use of digital infrared thermal imaging (DITI) to determine whether surface temperature gradient differences exist between pregnant and nonpregnant mares as a noncontact method to determine pregnancy status. On the day measurements were collected, each pregnant mare (n=10; beginning at 292.4+/-1.4 d of gestation) was paired with a nonpregnant mare (n=17). Ambient temperature, DITI measurements (left and right flank, wither temperatures [i.e., animal surface control] and background temperature), and rectal temperatures were obtained every 7 d for 5 wk before parturition and for 3 wk after parturition. There were no differences (P>0.10) in temperature of the left and right side within groups; therefore, data were pooled. Pregnant mares had a higher (P<0.01) flank temperature than that of nonpregnant mares (36.0+/-0.2 degrees C vs. 34.2+/-0.2 degrees C, respectively). Moreover, the difference (2.4 degrees C) in flank temperatures between the pregnant and nonpregnant mares was greater when the ambient temperature was <19 degrees C. Flank and wither temperatures were positively correlated (R=0.72; P<0.01) and were positively correlated with ambient temperature (R=0.48 and 0.64, respectively; P<0.01). However, wither temperatures (skin control site) did not differ (P>0.10) between pregnant and nonpregnant mares. In conclusion, late-gestation mares had higher flank temperatures than those of nonpregnant mares, regardless of environmental conditions, however discriminating abilities were greater when ambient temperature was lower. We inferred that DITI may have value in confirming mid- to late-gestation pregnancies in some species by noncontact means, as observed in the mare.