STUDY OF DOPPLER SONOGRAPHY OF CORPUS LUTEUM DURING THE BOVINE OESTRUS CYCLE

Doppler ultrasound has recently emerged as one of the main innovations in cattle practice and has mainly found application in the evaluation of luteal blood perfusion (LBF). It has been evaluated during different phases of the oestrous cycle, but the technique is poorly standardized [1-3]. Aim of the study was to evaluate visual and quantitative changes of size of corpus luteum (CL) and LBF in dairy cattle during an oestrous cycle at 2 follicular waves using colour flow mode (CFM) and power flow mode (PFM) doppler ultrasound. The study was preliminary approved by the Ethics Committee of the Department of Veterinary Sciences of the University of Messina (reference number 010/2016). Ten Friesian cows were selected and synchronized. The CL was evaluated at 3/4-day intervals until the next oestrus onset. The emergence of the 2 follicular waves was also monitored. After identifying the spiral luteal artery entry at the base of the CL, multiple scans of the vertical plane at the maximum diameter of the CL from the apex to the base were recorded in B-mode, CFM and PFM for each cow and session. An Esaote mylab 30 gold was employed with the following setting: pulse repetition frequency 2.1 (CFM) or 2.8 (PFM), gain 70%. The real area of CL (RACL) was calculated subtracting the area of the eventual inner cavity. The LBF was quantified off-line by means of a visual score and of an image analysis system (Digimizer 4.1) and expressed as percentage of coloured area on RACL. Student and ANOVA tests were used for statistical analysis. Data were presented as means and standard deviations. There were significant individual variations for the RACL and LBF, calculated in CFM. PFM was the most accurate method for evaluating LBF, although, at day 15-16, it was also affected by individual factors (p <0.01). The study of RACL and LBF during a 2-wave oestrous cycle distinguished 3 phases: a phase of CL formation (3-4 days) with LBF of 0.3±0.3 cm2 on a RACL of 3.1±0.9 cm2, a central phase (7-16 days) with LBF of 0.7±0.4 cm2 on a RACL of 4.8±0.8 cm2 and a regression phase (19-20 days) with a minimum LBF of 0.1±0.1 cm2 in a CL of 3.3±0.6 cm2. Visual score allowed easily differentiating these phases being powerful to recognize non-functional CLs (no blood flow) with relevant clinical applications. According to this study, there is no significant difference of LBF from 7 to 16 days of the oestrus cycle; although the RACL significantly changes in this period, the dimensional variations are too thin to be clinically appreciated. However, this study contributed to standardize the technique and to define the values of RACL and LBF during a 2-wave oestrous cycle of dairy cattle.