168 Comparison of different Doppler ultrasound settings for pregnancy diagnosis based on corpus luteum perfusion at 21 days after AI in beef cattle

Colour Doppler ultrasonography of the corpus luteum (CL) can be used for early pregnancy diagnosis to improve reproductive efficiency and increase the use of AI in beef cattle. The objective of the present study was to determine the diagnostic performance of different Doppler ultrasonography settings for pregnancy diagnosis based on CL perfusion at 21 days after fixed-time AI in beef heifers and cows. Yearling Angus-cross heifers (n = 25) and suckled Angus-cross cows (n = 84) aged 2-13 years were submitted to a 5-day CO-Synch + controlled internal drug release (CIDR) and timed AI at 60 or 72 h after CIDR removal for heifers and cows, respectively. Animals were evaluated by a single operator using colour Doppler ultrasonography (Esaote MyLab Delta) at Day 21. Three settings for colour flow mapping (720, 960, and 1500 Hz) and one setting for power Doppler (960 Hz), which differed in pulse repetition frequency, were evaluated. The other settings remained unchanged with a probe frequency of 6.3 MHz, wall filter of 3, and gain of 61. The pregnancy status (pregnant or non-pregnant) of cows and heifers was determined at 21 days following insemination using colour Doppler ultrasonography. Cows and heifers were considered to be pregnant if the CL blood flow area covered >10% of the periphery of the CL and contained at least two colour internal tracts penetrating towards the centre of the CL. Cattle were evaluated using transrectal B-mode ultrasonography on Day 35 to determine actual pregnancy status. Differences between diagnostic performance variables were evaluated using logistic regression, and setting, category (heifer or cow), and the interaction were included as fixed effects. Pregnancies per AI at Day 35 after fixed-time AI were 47.7% (52/109). Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for pregnancy diagnosis at Day 21 for each setting are included in Table 1. There were no differences in sensitivity and NPV between settings (P > 0.9), category (P > 0.9), or the interaction (P > 0.9). There was no effect of setting (P > 0.5) or category × setting interaction (P > 0.8) on specificity and PPV. There was, however, an effect of category (P < 0.01). Colour Doppler ultrasonography had less specificity (59.1% compared with 90.2%) and PPV (75% compared with 89.3%) in heifers than in cows. In conclusion, colour Doppler ultrasonography settings that were evaluated did not affect the diagnostic performance for pregnancy diagnosis at Day 21 after AI, although, numerically the colour flow mapping at 960 Hz appears to maximise diagnostic accuracy. In addition, the false-positive rate was greater in heifers, which warrants further research. Table 1.Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for pregnancy diagnosis for four colour Doppler ultrasound settings (colour flow mapping (CFM) at 720, 960, and 1500 Hz and power Doppler (PWD) at 960 Hz) at 21 days after fixed-time AI Item CFM720 CFM960 CFM1500 PWD960 Sensitivity, % 100 100 92.3 100 Specificity, % 80.7 87.7 87.7 80.7 PPV, % 82.5 88.1 87.3 82.5 NPV, % 100 100 92.6 100