Use of B-mode ultrasound and grey-scale analysis to study uterine echogenicity in the pig

This study was conducted to determine uterine echogenicity by grey-scale analysis (GSA) and transcutaneous ultrasonography in pregnant sows (P-sows; n=16) and gilts (P-gilts; n=13) vs. cyclic gilts (C-gilts; n=9) between days 8 and 16 post ovulation (po) with the aims of testing for feasibility of uterine GSA and of gathering reference data. Estruses and ovulations were hormonally synchronized and the animals artificially inseminated. Ovulation was monitored by ultrasound. The equipment used was a HS 2000 ultrasound unit and a 5 MHz linear probe. Unit settings were standardized for all GSA scanning sessions and the animals crated during scanning. For GSA, cross-sections of the uterine horns were imaged, entirely defined as regions of interest, and pixel analyses done. A total of 342 scanning sessions were performed, 341 GSA accomplished, and 1-13 cross-sections analyzed per session. Comparison of coefficients of variation suggests that analysis of two cross-sections per session is sufficient for a reliable GSA per animal. P-sows and P-gilts were similar in their echogenicity course, but differed from C-gilts. Most noticeable, echogenicity declined in pregnant animals on day 12 po, while it increased in cyclic gilts. In conclusion, the study demonstrates that GSA using transcutaneous ultrasound is a feasible procedure for the determination of uterine echogenicity in the pig, and that pregnant and cyclic pigs differ in the uterine echogenicity, particularly during the time when maternal recognition of pregnancy occurs.