The relationship between corpus luteum area, blood supply parameters and serum progesterone concentration in cycling mares

To identify correlations between serum progesterone concentrations in mares, corpus luteum area, and blood flow parameters in the corpus luteum using Power-Mode Doppler Doppler images, a study was conducted in natural cycles and cycles with induced luteolysis. A comparison of visual blood flow assessment and the results of a computerized image analysis system using ImageJ was also conducted. Ultrasound examinations were performed on 10 mares from the experimental stable of the All-Russian Research Institute of Equine Breeding. Using computer analysis of corpus luteum Doppler images, the above characteristics were determined during the following periods: days 0—4, 5—7, 8—12, and 13—16 of the mares’ estrous cycle (day 0 is ovulation day). Statistical processing of the data was performed using Excel and Statistica 12. Differences between periods were assessed using the nonparametric Mann-Whitney U-test with a significance level of p < 0.05. Processed data by period are presented as the median (M) and upper and lower quartiles (LQ-UQ). The relationship between parameters was calculated using the Spearman correlation coefficient. Analysis of the correlation coefficient revealed a moderate positive relationship between serum progesterone concentration and blood flow area and the blood flow intensity score (r=0,33 and r=0,3; p<0,05). A strong positive relationship (r=0,7—0,8; p<0,05) was established between the assessment of blood flow parameters using a computer analysis system (ImageJ) and the visual assessment of blood flow score. During induced luteolysis, a strong positive correlation (r=0,82; p<0,05) was found between progesterone concentration and corpus luteum area, and a significant positive correlation (r=0,66; p<0,05) was found between corpus luteum area and blood flow area. These data may have useful prognostic value when assessing the functional activity of the corpus luteum in mares.

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