Using Doppler ultrasonography on day 34 of pregnancy to predict pregnancy loss in lactating dairy cattle

The objective of this experiment was to determine whether uterine or ovarian vascular dynamics could be used to identify cows at risk for pregnancy loss. Our hypothesis was that cows that subsequently lose their pregnancy will have decreased corpus luteal (CL) perfusion, or an increased resistance index (RI; reduced blood flow), or both, at d 34 of pregnancy. Day 34 was chosen because it is a common time for dairy cattle to be checked for pregnancy. This experiment was performed in 2 replicates from November 2011 to April 2012 (n = 69) and from November 2012 to April 2013 (n = 53). Cows were bred via timed artificial insemination using Ovsynch-56 and checked for pregnancy on d 32 after artificial insemination. At d 34, cows confirmed pregnant were examined via transrectal Doppler ultrasonography. Blood samples collected via coccygeal vein were used to measure circulating plasma progesterone concentrations. Diameter of the corpus luteum and crown-rump length were measured. Color power Doppler ultrasonography was used to determine vascular perfusion to the CL, and RI was measured for the uterine arteries just after branching from the umbilical artery. Records were later examined to identify pregnancy status of cows after reconfirmation. Abortion rate did not differ between replicates (11.6% in replicate 1, 9.4% in replicate 2). Mean crown-rump length of embryos that were carried to term was greater on d 34 than that in cows that aborted (14.23 ± 0.27 vs. 13.21 ± 0.53 mm). Circulating progesterone concentration at d 34 was greater for cows that carried pregnancies to term than for those that aborted (9.1 ± 0.7 vs. 7.5 ± 1.0 ng/mL). The final logistic regression model consisted of crown-rump length, progesterone concentration, and RI of the uterine artery contralateral to pregnancy. Decreased crown-rump length and progesterone concentration tended to be associated with increased odds ratio for pregnancy loss, whereas CL perfusion and uterine blood flow were not associated with increased odds ratio of pregnancy loss. In conclusion, examining CL perfusion and RI of the uterine arteries on d 34 of pregnancy does not offer a method to identify lactating Dairy cattle at risk for pregnancy loss after d 34.