Ultrasound-Based Reproductive Monitoring

Ultrasonography was performed following Sulikowski et al. (30 ). Briefly, an Ibex EVO II portable ultrasound (EI Medical Imaging) with a 60-mm curved linear array 2.5- to 5-MHz transducer (model 290470) capable of a 24-cm scan depth was used to obtain images of the reproductive tract of each female. Scanning was performed on the ventral surface from the pectoral to the pelvic fin in both a transverse and longitudinal orientation to obtain cross-sectional and lengthwise images, respectively. Depth of the scan ranged from 12 to 24 cm, depending on the image being obtained. Collected images and video loops were saved on the Ibex Pro at the time of sampling. Gravidity was determined on the basis of the presence or absence of embryos. Images and frozen video stills were then used to measure (via proprietary software preinstalled on the Ibex EVO II ultrasound) pup diameter (centimeters) along the transverse axis.