Relationship between mammary blood flow, infrared thermography and ovine placental lactogen during the periparturient period in ewes

Abstract

The aim of the study to verify the hypothesis whether a drop in the oPL levels in the blood in the periparturient period is associated with changes in the right mammary vein blood flow (RMVBF) and udder skin temperature (UST). We were also interested in comparing variations in the above-mentioned parameters in single- and twin-pregnant ewes. Beginning six days before parturition (-6th day) until four days postpartum (4th day), every second day each of 15 experimental pregnant ewes was subjected to color Doppler ultrasound performed with continuous wave-equipment (My Lab One/Touch) and infrared thermography (IRT), which allowed for noninvasive collection of data. Plasma oPL levels were determined using quantitative sandwich ELISA Kit specified for sheep placental lactogen 1 (oPL). The measured values of UST were affected by the periparturient period but not by the number of lambs delivered. The highest udder temperatures were recorded at four days before parturition, which was followed by their gradual decrease. As a result, UST achieved the lowest values in single- and also in twin-pregnant ewes on the day of parturition (35.70 ± 0.65°C and 35.42 ± 0.45°C, respectively). Among all the time points of measuring IRT and oPL, a significant positive correlation (P≤0.01) was estimated at -4 and 0 days before parturition for single- (r= 0.99) and twin- (r= 0.59) pregnant ewes. In comparison to control ewes, right mammary vein blood flow (RMVBF) significantly (P≤0.05) increased in all pregnant ewes under study. Especially in twin-pregnant ewes, a positive correlation between the plasma concentration of oPL and blood flow occurred between the -4th and 0 day (r = 0.76). Maximal velocity of blood flow in the mammary vein in single- (25.90 ± 5.95 cm/s) and twin-pregnant ewes (24.62 ± 4.86 cm/s) was recorded at the 2nd and 4th day postpartum, respectively. The highest values of plasma oPL (0.56 ± 0.05 µg/ml) recorded at the beginning of the experimental period (-6 days before parturition) dropped significantly (P≤0.05) during the subsequent days, until parturition. The curve of the temporal changes in the concentrations of plasma oPL remains unchanged regardless of the number of fetuses. Three-phasic thermal changes in the periparturient period and an increase in blood flow parameters are related to the disappearance of oPL from the circulation, which should be taken into account when assessing a pathological state of this gland.