AASRP Research Summary
Ultrasonographic analyses of fetal gastrointestinal characteristics and correlations with gestational age and maturity in sheep
| Date/Time: |
9/12/2025
17:00
|
| Author: |
Jenna Bayne |
| Clinic: |
Auburn University College of Veterinary Medicine |
| City, State, ZIP: |
Auburn, AL 36849 |
J.E. Bayne , DVM, PhD, DACVIM
1
;
E. van Santen , PhD
2
;
R.C. Cole , DVM, DACVR, DAVCR-EDI
1
;
1Department of Clinical Sciences, Auburn University College of Veterinary Medicine, Auburn, AL
2Statistical Consulting Unit and Agronomy Department, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL
Introduction:
Using ultrasonography to assess pregnancy status, fetal well-being, and estimation of gestational age is a standard diagnostic tool used in livestock. In late gestation small ruminants, there is often the need to estimate gestational age and the viability and readiness of the lamb or kid in emergent circumstances (e.g., pregnancy toxemia). The onset of characteristics suggestive of organ maturation and function has recently been explored in veterinary species. The ability to visualize and demonstrate the onset of gastrointestinal (GI) tract motility sonographically may be a useful measure for estimating fetal maturity, as it is one of the last organs visualized and used as a clinical indication of reaching full-term gestational length. The first objective of this study was to describe the ultrasonographic characteristics and the progressive changes observed in the fetal gastrointestinal tract (GIT) in late gestation ewes and utilizing these data, we propose a fetal GIT scoring system in sheep. The second objective was to determine the probability of identifying fetal GIT characteristics that change with advancing gestational age.
Materials and methods:
Twelve healthy adult Katahdin ewes were enrolled in the study. The breeding group was exposed to a single ram, fitted with a marking harness, with marked ewes removed every 24 h. Transabdominal ultrasound was performed at day 30 – 45 of gestation to determine pregnancy status and estimate fetal numbers. On day 120 of gestation, a more detailed sonographic assessment was initiated. Exam frequency increased with advancing gestation, i.e., every 24-48 h after 138 days gestation until parturition. Parameters determined included fetal heart rate, cardiac size, and GI characteristics. A grading scale based on studies in other species was applied, specifically for the onset and progressive changes in intestinal wall definition, luminal content characteristics, peristalsis, and segmental dilation. Based on these characteristics, a GI score (1 – 4) was assigned to each fetus during serial ultrasonographic examinations until term (median 148 days). The relationship between response variables was modeled using various linear and generalized linear regression techniques implemented in SAS® PROC CLIMMIX (SAS/STAT 15.2; SAS Institute, Cary, NC).
Results:
A total of 10 pregnancies (10/12 ewes) were serially evaluated and represented 23 fetuses. In 8/10 ewes, all lambs were born vaginally without intervention, with a median gestation length of 148 days. With advancing gestational age, progressive maturation and increasing GI scores were observed, with probabilities greater than 90 % for detecting GI scores of 3 and 4 at term. Intestinal wall definition was well-defined with 50 % and greater than 90 % detection probabilities at days 130 and 132 of gestation, respectively. The onset of detectable motility was similar for the forestomach, abomasum, and intestines between 126 and 130 days of gestation. A greater than 90 % probability of detecting motility of the forestomach, abomasum, and intestine were present at 148-, 148-, and 138-days gestation, respectively. As gestational age advanced, intestinal luminal content changed from mixed echogenic to anechoic, and the onset of purposeful segmental dilation progressed from occasional to rhythmic in frequency. At term, there was approximately 90 % or greater probability of observing anechoic luminal content and rhythmic segmental dilation, respectively.
Significance:
An ordered progression in the probability of identifying GIT characteristics with progressive signs of fetal maturation was demonstrated for intestinal wall definition, forestomach and intestinal motility, changes to the intestinal luminal echogenicity, and the increasing frequency of intestinal segmental dilation. The probability of GI scores characterized by easily well-defined intestinal walls, content, segmental dilation, and rhythmic to continuous peristalsis was over 90 % at term. Further studies are needed to determine whether GI scores can predict fetal readiness and perinatal outcomes in healthy and compromised pregnancies.
