Association between the Area of the Highest Flank Temperature and Concentrations of Reproductive Hormones during Pregnancy in Polish Konik Horses—A Preliminary Study

Abstract

Determination of the pregnancy status is one of the most important factors for effective pregnancy management. Knowledge of the stage of pregnancy is important to interpret many of the reproductive hormones’ concentrations, including progesterone (P4), estrone sulfate (E1S), 17-ß estradiol (E2), and relaxin (REL). However, it is limited in wildlife or captive equids that cannot be handled. Reproductive hormones affect regional blood flow, the proliferation of tissues, and local metabolism intensity. Therefore, this preliminary study aimed to assess changes in thermal features of the abdomen lateral surface and concentrations of reproductive hormones in Polish native pregnant mares. The study was carried out on 14 non-pregnant and 26 pregnant Polish Konik mares during eleven months of pregnancy. Infrared thermography was conducted to image the lateral surface of mares' abdomen (Px1) and flank area (Px2); P4, E1S, E2, and REL concentrations in serum were also determined. The evidence of the association between the area with the highest temperatures (Area of Tmax) and serum concentrations of P4 (the slope = 1.373; p = 0.9245) and REL (the slope = 1.342; p = 0.4324) were noted dependent across months of pregnancy. Measures of superficial body temperatures were found to change monthly, similarly to ambient temperatures, with no evidence of coincidence with changes in reproductive hormone concentrations. Individual thermal characteristics of the lateral surface of the abdomen differed between pregnant and non-pregnant mares in other periods. Differences in maximal and average temperature and Area of Tmax were observed from the sixth month of pregnancy, and those in minimal temperature were observed from the eighth month.

Advances in Thermal Image Analysis for the Detection of Pregnancy in Horses Using Infrared Thermography

“…It should be highlighted that homogeneity of data sets obtained from thermal images from the control group, in this research the non-pregnant group, is crucial for accurate group distinction [ 12 , 21 , 52 , 53 ]. Information obtained from thermal images of normal horses [ 18 , 20 , 54 ] provide a baseline of the expected values in the imaged area when comparing to the physiological [ 7 , 8 , 55 ] and pathological [ 13 , 56 , 57 ] changes observed in experimental groups. In the case of the abdominal area in mares, the maximal, average, and minimal temperatures on normal thermal images were recently reported [ 7 , 8 , 9 ] both for non-pregnant and pregnant mares.…”

“…Information obtained from thermal images of normal horses [ 18 , 20 , 54 ] provide a baseline of the expected values in the imaged area when comparing to the physiological [ 7 , 8 , 55 ] and pathological [ 13 , 56 , 57 ] changes observed in experimental groups. In the case of the abdominal area in mares, the maximal, average, and minimal temperatures on normal thermal images were recently reported [ 7 , 8 , 9 ] both for non-pregnant and pregnant mares. In previous research, the Gaussian distribution test was the only test used to explore the homogeneity of data.…”

“…The thermal image processing steps for conventional analysis of IRT measures included (i) image acquisition, (ii) segmentation of regions of interests (ROIs), and (iii) extraction of thermal features (the maximal temperature, the average temperature, the minimal temperature, and the area of the maximal temperature). Results from conventionally processed thermal images were previously documented [ 8 , 9 ].…”

“…Thus, there is a need for the development of accurate, noninvasive, and contactless methods for pregnancy detection. Infrared thermography (IRT) is considered a valuable diagnostic method, which has previously been adapted to evaluate pregnancy in females of different species, such as zebras, rhinoceros, giraffes [ 4 ], pandas [ 5 ], cattle [ 6 ], and horses [ 7 , 8 , 9 ]. IRT measures the infrared spectrum of electromagnetic radiation emitted from the body surface [ 10 ].…”

“…The surface body temperature gradients imaged in the abdominal area can be influenced by ambient temperature fluctuations [ 14 , 15 ], other weather conditions [ 10 , 16 ], and individual properties of horses’ body surface [ 17 , 18 , 19 ]. A high level of repeatability can be achieved and maintained in thermal images using standardized conditions of image acquisition [ 20 , 21 ]; however, the length of time it takes to detect pregnancy related surface temperature changes [ 7 , 8 ] and the accuracy of pregnancy detection [ 9 ] limit the application of IRT to the late stage of pregnancy. Therefore, this work focused on developing a methodology for the detection of pregnancy in mares by building a multifactorial approach for digital thermal image processing.…”