Doppler sonography of the corpus luteum during the oestrus cycle in dairy cows

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). LBF has been evaluated during different phases of the oestrous cycle, but the technique is poorly standardized. The 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. Ten Friesian cows were selected and synchronized. The CL was evaluated at 3/4-day intervals until the next oestrus onset. 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 vet 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). 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 when calculated in CFM. PFM minimized these variations, although, at day 15-16, it was also affected by individual factors (p < 0.01). The combined 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. 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 defining the values of RACL and LBF during a 2-wave oestrous cycle of dairy cattle.