Macroscopic characteristics of the umbilical cord in Standardbred, Thoroughbred and Warmblood horses

The umbilical cord (UC), the connection between mother and fetus via the umbilical vessels, carries nutrients and oxygenated blood to the fetus through the umbilical vein and removes deoxygenated blood and waste products via the umbilical arteries. It is designed to protect blood flow to the fetus during pregnancy. In equine medicine, only a few studies have described the UC, and most of these involved Thoroughbreds. The present study describes and compares the macroscopic features of the equine umbilical cord in three different breeds and in relation to the foal's gender. In addition, a possible correlation between UC features and maternal and perinatal factors is investigated. One hundred and twenty four healthy mares with normal pregnancies were enrolled in the study and were divided into three groups according to their breed: 70 Standardbreds (STB), 38 Thoroughbreds (THB) and 16 Warmbloods (WAB). The following data were recorded: mare's age and parity, gestation length, placental weight, presence of fetal membrane alterations, UC length and number of coils in the amniotic and allantoic portions, and the Umbilical Coiling Index (UCI), which is the ratio between total coils and total UC length. The UCI has not been investigated previously in veterinary medicine. Furthermore, immediately after foaling, APGAR score, foal's weight and sex were recorded. All the STB and WAB were housed in Italy and the THB were housed in New Zealand. Mares’ mean age was higher in WAB than in THB and STB; the latter had a significantly shorter gestation length. The foal's weight was positively correlated with placental weight in all breeds; and in STB, foal weight was positively related to parity and gestation length. Mean total UC length was comparable to previous reports in THB, STB and WAB. The lengths of the two UC portions were statistically different between STB and THB, where the amniotic portion was longer than the allantoic one. In each breed, total UC length was correlated with total number of coils (THB and STB = 5 ± 1; WAB = 6 ± 1), the UC amniotic length was positively correlated with the number of amniotic coils and the allantoic length was positively correlated with the number of allantoic coils. The UCI values were 0.09 in STB and THB and 0.1 in WAB. This study provides reference values for UCI that could be included in the gross placental evaluation if its clinical importance were demonstrated.