Sonographic appearance of the late gestation equine fetal intestine.

This research study explored how ultrasound can be used to observe the development of a horse fetus’s gastrointestinal (GI) tract in order to better predict when the horse may be ready for birth. The development of the estimated delivery date was based on the observation of seemingly correlated factors such as stomach rugae, peristalsis, intestinal contents, tail head relaxation, and udder development.

Research Context

• The study addresses the difficulty of predicting the birth of a mare’s foal due to varying gestation periods. Because there is no conclusive method, this research project attempted to identify indicators of fetal maturity based on changes in the gastrointestinal (GI) tract as viewed through sonographic examinations.

Research Methodology

• A single observer conducted weekly ultrasound examinations of horse fetuses around 2-3 weeks before their expected due date of 330 days. Criteria such as presence of stomach rugae, the definition and dilation of bowel segments, the intestinal contents, and signs of peristalsis were assessed.
• Based on the criteria, a five-phase grading system was developed, with phase one presenting as a uniform grey area below the diaphragm and the remaining phases differentiated mostly by the frequency of peristalsis.
• The data set for these observations were restricted to pregnant mares that experienced a normal birth and had healthy foals.
• Simulation-based bootstrap approach with 1000 replicates using Stata 14 was used to validate the associations between the sonographic features and days prepartum.

Key Findings

• The research found that all five gestational criteria – stomach rugae, peristalsis, intestinal contents, tail head relaxation, and udder development – were significantly correlated with the days before birth.
• Further, the study found that a multiple linear regression model including tail head relaxation and peristalsis could predict the days to birth within a 95% confidence interval of 6 days. When day of gestation was included as an additional variable, the confidence interval narrowed to 4 days.
• The authors suggest this method can provide important insight into fetal maturity. However, they also recommended further experiments comparing high-risk mares to typical ones to confirm the reliability of this approach in a clinical setting.