Real-time transrectal ultrasonographic measurement of the fetal eye (vitreous body) to predict parturition in bucking horse mares.

This study examined the use of ultrasonography to predict when bucking horse mares, with unknown breeding dates, would give birth. By measuring the size of the unborn foal’s eye, specifically the length of the vitreous body within the eye, researchers developed an equation that can accurately predict the days before parturition (DBP) specific to this breed.

Research Methodology and Outcome

• The study was carried out by conducting transrectal ultrasounds on pregnant mares over two years. From 240 reproductive examinations, 199 pregnancies were identified, and of these, the fetal eye was successfully identified and measured in 155 cases.
• Confirmation of foaling dates (the actual date the foals were born) for 131 successful eye measurements allowed the researchers to calculate DBP. The length of the fetal eye was measured at the level of the lens, in the largest dimension of the vitreous body, with lengths ranging from 9 to 35 mm.
• A mathematical statistical procedure known as multilevel mixed-effects linear regression was used to develop a curvilinear equation. This equation helps predict the DBP of bucking horses based on the ultrasonographic measurement of the fetal eye.
• The equation developed was:
  DBP= -0.163(fetal eye length measurement in mm)  + 268.949, with a correlation (r) of 0.881, a p-value of less than 0.001 (signifying statistical significance), concordance of 0.994, and an average difference of -0.077±17.214 days.

Comparison With Previous Studies

• Despite the developed equation sharing similarities with a previously reported equation used for small ponies, applying the small ponies’ equation to predict DBP in bucking horse pregnancies resulted in a minor, yet significant underestimation of prediction in DBP for bucking horses.
• This implies that the breed-specific parameters are indeed necessary for the development of accurate prediction equations, as the study initially proposed.

Implications of the Study

• Being able to accurately predict the birth of foals can assist in making necessary preparations and ensuring optimal care for both the mare and the newborn foal. This is particularly useful in herds of animals where breeding dates are unknown.
• The method used in this study, based on the ultrasonographic measurement of the fetal vitreous body length, adds to the existing knowledge and provides a valuable tool for breed-specific parturition prediction in bucking horses.