Equine fetal kinetics: entry and retention of fetal hind limbs in a uterine horn.

The research studies the progression of fetal positioning in pregnant pony mares through ultrasound imaging, focusing on the movement and final settling of fetal hind limbs in one uterine horn.

Methodology

• The study utilized transrectal ultrasonic examinations on 31 pony mares that were pregnant. The examinations took place weekly during the 6th to 11th months of pregnancy.
• The uterine horn of each pregnant mare was divided into three approximate equal parts; the caudal (rear section), middle, and cranial (frontal section).

Findings

• The study discovered that the percentage of instances with the fetus’ cranial (head) side first increased significantly from 58% at month 6 to 99% at month 9.
• The occurrence of the fetal hind limbs entering a uterine horn was consistent among all subjects. This entry was initially hesitant but became definitive around day 230 +/- 2.2 of pregnancy.
• Detailed tracking revealed common retraction of limbs after they entered the rear and middle parts of the horn in the initial months (months 7 and 8).
• It was found that both uterine horns were closed in 86% of mares during the ultrasound preceding the final entry of hind limbs into one of the horns.
• By months 9 and 10, the hind limbs had reached the frontal part of the horn in most of the cases examined (73% and 98% respectively).

Observations

• The study showed that the size of the uterine horns, as visualized on the ultrasound, increased significantly from months 7 to 10.
• A reversal was observed between months 10 and 11, which manifested as a decrease in the size of the horn containing the hind limbs. This was attributed to the thinning of the wall of the horn above the metatarsal bone and a hoof, and the flattening of the horn.
• The researchers detected apparent placental fluid in the area between the hind limbs and the cornual (corner) wall.
• This fluid increased progressively over the months, being detected in 0% of cases in month 8, 10% in month 9, 25% in month 10, and 63% in month 11. By month 11, the uterine horn containing the fetal limbs typically contained this placental fluid.

Conclusion

The research discovered that the process of the fetal hind limbs entering a uterine horn is initially tentative. It becomes final by around the 8th month of pregnancy. The link between the cornual wall and the limbs is close from months 7 to 11. By the 11th month, the uterine horn accommodating the fetal limbs often appears thinner and flatter, usually filled with placental fluid.