Factors associated with the differential in actual gestational age and gestational age predicted from transrectal ultrasonography in pregnant dairy cows

Establishment of fetal age equations based on ultrasound measurements in cross-bred Holstein cows

“…The estimation of the day of pregnancy is a frequently requested application of ultrasonic imaging in cattle after aging pregnancy using fetal measurements has proven to be accurate [12,27]. Most of modern ultrasound scanners are embedded with fetal age equation of pure-bred Holstein cows based on measurements of various structures, most popularly created by White et al [22] and Kahn [23].…”

“…One of the main advantages of using ultrasound is early detection of pregnancy, usually after 27 d post-breeding [6,8,9]. Other advantages include monitoring fetal development and viability as well as estimating fetal age and sex [10][11][12].…”

“…Fortunately, aging pregnancy using fetal measurements has proven to be accurate [12][13][14][15] i.e., by measuring of crown-rump-length (CRL), of which determined along the direct line between the crown and the ischium. CRL, however, may only be determined over a relatively short period due to the limited size of the screen of most ultrasound scanners.…”

“…CRL, however, may only be determined over a relatively short period due to the limited size of the screen of most ultrasound scanners. It is hardly possible to correctly measure CRL once the fetuses have reached a length of more than 10 cm [12,16,17]. Trunk diameter (TrD), a suitable measurement can be made whether the images are in cross section or longitudinal section, but a cross section may be preferred.…”

Estimating fetal age: how accurate is it really?

“…Nevertheless, almost all reports of fetometry and fetal age (from White et al 1985to Lazim et al 2016) have focussed on correlation and regression rather than accuracy. One study (Fitzgerald et al 2015), which claimed to have evaluated ultrasonography as a predictor of gestational age, just reported mean difference between predicted and actual values, with no measure of precision at the individual cow level. Lawrence et al (2016) were unable to find any studies of fetometry suitable for directly comparing with their data on fetal age and placentome size.…”