9 Performance of color Doppler ultrasonography of the corpus luteum for pregnancy diagnosis in beef heifers with or without a controlled internal drug release at different days after fixed-time artificial insemination

Abstract

Colour Doppler ultrasonography (CDU) of the corpus luteum (CL) has the potential to be used for early pregnancy diagnosis in order to improve reproductive efficiency and increase the use of fixed-time AI (FTAI) in beef cattle. The objective of the present study was to determine the sensitivity and specificity of CDU of the CL for pregnancy diagnosis in beef heifers with or without a CIDR at different days after FTAI. Angus-cross beef heifers (n = 84) were synchronized using a 5-day Co-Synch with AI at 60 h after CIDR removal. On Day 15 post-AI, heifers were randomly assigned to receive a CIDR (Eazi-Breed CIDR, Zoetis, Parsippany-Troy Hills, NJ) for 9 days or remain as untreated controls. Heifers were evaluated by transrectal CDU (MyLab Delta, Esoate, Genoa, Italy; 7.5-MHz linear array probe, pulse repetition frequency = 960 Hz) at 15, 17, 20, and 22 days post-AI. Heifers were determined to be pregnant by CDU if colour pixels covered >10% of the periphery of the CL and contained at least 2 colour internal tracts penetrating toward the centre of the CL. Heifers were evaluated by B-mode ultrasonography on Day 28 to determine true pregnancy status. Differences between days and treatments were evaluated using generalized estimating equations. Pregnancies per AI at Day 28 after FTAI were 53.6% (45/84) and were not different between CIDR (52.4%; 22/42) and control (54.8%; 23/42) heifers (P = 0.83). Sensitivity and specificity for CIDR and control heifers at different days are shown in Table 1. There was no effect of treatment (P = 0.49), day (P = 0.99), or treatment by day interaction (P = 0.99) on test sensitivity. Specificity was different (P < 0.01) between days; however, no treatment (P = 0.91) or treatment by day interaction (P = 0.82) was identified. Specificity was lowest on Days 15 and 17 and increased to reach its maximum at Day 22. Although no differences between treatments were observed, specificity on Day 22 was numerically greater in CIDR-treated heifers. Positive and negative predictive values for CDU at Day 22 were 84 and 94.1%, respectively, for CIDR-treated heifers and 79.3 and 100%, respectively, for control heifers. Cohen’s Kappa indicated slight (0.19), fair (0.27), moderate (0.50), and substantial (0.73) agreement between conventional ultrasound at Day 28 and CDU at Days 15, 17, 20, and 22, respectively. In summary, CDU showed excellent sensitivity between Days 15 and 22, indicating a very low rate of false-negative results. However, high specificity (low false-positive rate) was achieved only at Day 22. Thus, pregnancy diagnosis by CDU at Day 22 after FTAI coupled with the use of a CIDR may be an effective strategy to identify nonpregnant heifers and attempt their prompt resynchronization.

Table 1.  Sensitivity and specificity (%) for pregnancy diagnosis by CDU in beef heifers with or without a CIDR at different days after FTAI