Transrectal ultrasonography of the caudal placental pole and fetal eyeball diameter and associations with the season, duration of gestation, placental weight, sex of the foal, and birthweight in donkeys☆.
Authors: Magalhaes Humberto B, Canisso Igor F
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Researchers in this 2022 study monitored 121 pregnant donkeys via transrectal ultrasonography at 15-day intervals from day 120 of gestation through to parturition, measuring placental thickness, fetal eyeball diameter, and fluid characteristics to establish normal reference ranges and identify factors influencing pregnancy duration and foal development. Gestation length in donkeys averaged 365.4 ± 10.4 days, with meaningful variation based on breeding season and foal sex: spring-bred females carried their foals approximately 16 days longer than summer- or autumn-bred animals, whilst colts remained in utero around four days longer than fillies. Combined uterine and placental thickness increased in a sigmoid pattern as pregnancy advanced but was unaffected by season or foal sex, whilst fetal eyeball diameter proved a reliable biometric indicator of gestational age (r=0.78); notably, chorioallantois oedema became increasingly prevalent and severe between days 240 and 300 of gestation. For equine practitioners, these findings provide species-specific pregnancy benchmarks for donkeys—a notably under-researched population—enabling more accurate foetal age estimation via eyeball measurement and clearer expectations around gestation duration based on breeding season and anticipated foal sex, ultimately supporting more informed decision-making around timing of intervention in problematic pregnancies.
Read the full abstract on PubMed
Practical Takeaways
- •Transrectal ultrasonography can reliably estimate gestational age in donkeys using fetal eyeball diameter measurements, with strong correlation to actual gestation stage
- •Account for breed/season effects when predicting parturition in donkeys; spring-bred animals carry pregnancies 16 days longer than other seasons, and colts gestate 4 days longer than fillies
- •Monitor for chorioallantois edema and increased amniotic fluid echogenicity in late gestation (240-300 days) as normal pregnancy progression markers in donkeys
Key Findings
- •Mean gestation duration in donkeys was 365.4 ± 10.4 days, with spring-bred jennies having 16 days longer gestation than summer- and fall-bred animals (P < 0.0001)
- •Male foals had 4 days longer gestation than female foals (P = 0.0001)
- •Fetal eyeball diameter was strongly associated with gestational age (r = 0.78) and can be used as a predictor of gestational age
- •Combined thickness of uterus and placenta displayed sigmoid increase throughout pregnancy and was affected only by gestational age, not season or fetal sex (P < 0.0001)