Evaluation of ovarian volume by transrectal ultrasonography in cattle; affect of the day of the estrous cycle and validation of a method of subtracting of corpora lutea and follicle volume.

This research was conducted to evaluate a method for determining ovarian volume using ultrasonography; specifically, how the day of the estrous cycle affected ovarian volume, and the application of a formula for adjusted ovarian volume (ADJ VOL) and its relationship to actual ovarian volume. Cows (n = 22) were estrous synchronized and subjected to serial transrectal ultrasonographic evaluations, performed every 48 h from the day prior to ovulation until day 9 of the subsequent estrous cycle. Measurements obtained from recorded ultrasonographic images were used to determine actual ovarian volume cm3 = [0.523 X (D1 X D2 X D3)] and adjusted ovarian volume (ADJ VOL) cm3 = [0.523 X (D1 X D2 X D3)]- 43 (πrCL2) - 43 (πrF2) on days 1, 3, 5, 7, 9 of the estrous cycle. A third objective was to evaluate the concordance correlation coefficient (ρc) between post-mortem ovarian measurements and the water displacement test. Ovarian volume increased with each day of the estrous cycle from Day 1 to Day 7. Day of the estrous cycle affected ovarian volume (P <  0.001). When applying the formula for ADJ VOL, there was not an effect of day of the estrous cycle (P  = 0.509). Ovarian volume, results ex-vivo, were very consistent with the displacement volume results (ρc = 0.942). If large ovarian structures are present, and the day of the estrous cycle is unknown, then the formula for ADJ VOL can be used to estimate ovarian volume on Day 1 of the estrous cycle.