Wendy E. Vaala

Ultrasonographic assessment of fetal well‐being during late gestation: development of an equine biophysical profile

Mares with complicated pregnancies (illness, problems at parturition or delivery of an abnormal foal, n = 30) were scanned transabdominally from 298 days gestation to term in order to measure fetal size, evaluate fetal well-being and characterise the intrauterine environment. The results of the last scan obtained prior to parturition were compared to normal data obtained from fetuses of comparable gestational age to develop a biophysical profile specific for the equine fetus. Twelve mares produced a normal foal (positive outcome) and 18 mares delivered 19 abnormal foals (negative outcome). Both fetuses that were inactive throughout the entire scan and 4 of 5 fetuses with heart rate abnormalities were abnormal at birth. Three of 4 fetuses surrounded by decreased allantoic fluid quantities had a negative outcome. All mares with large anechoic spaces between the uterus and placenta (n = 3) and/or thickened uteroplacental units (n = 5) delivered abnormal foals. There was a significant correlation between fetal aortic diameter and neonatal foal weight in these complicated pregnancies (P<0.0001, r = 0.85). Fetal aortic diameters were predicted from maternal weight and 6 fetuses had smaller than predicted aortic diameters, all with negative outcomes. A biophysical profile of the equine fetus from 298 days gestational age to term was developed that included 6 factors related to pregnancy outcome: fetal heart rate, fetal aortic diameter, maximal fetal fluid depths, uteroplacental contact, uteroplacental thickness and fetal activity. The profile proved informative about fetal well-being, perinatal morbidity and perinatal mortality. A low score was a definite indication of an impending negative outcome; however, a high score was not assurance of a positive outcome. The utility of such a biophysical profile and future directions for research are discussed.

Management strategies for mares at risk for periparturient complications

Perinatal death accounts for a large percentage of foal mortality. The most serious threats to perinatal survival remain septicemia, hypoxia, and dysmaturity. Topics discussed in this article include biochemical indices of fetoplacental function and evaluation and management of the high-risk mare.

Evaluation of Systemic Relaxin Blood Profiles in Horses as a Means of Assessing Placental Function in High-Risk Pregnancies and Responsiveness to Therapeutic Strategies

Placental insufficiency is regarded as the primary factor contributing to late‐term abortion and perinatal death of foals. Often when problems associated with late‐term pregnancy in the horse are manifest the condition is well‐advanced and therapeutic intervention may not be effective in rescuing the pregnancy. If a compromised pregnancy due to placental insufficiency could be identified early, the pregnancy might be sustained through medical intervention. Because the placenta is the sole source of circulating relaxin in the mare, we hypothesized that systemic relaxin may serve as a biomarker of placental function and fetal well‐being and a predictor of pregnancy outcome at delivery. To test this hypothesis we monitored plasma relaxin in mares (light breeds) with normal and problematic pregnancies from clinical cases presented to the veterinary hospital and in pregnant mares experimentally inoculated with Streptococcus equi zooepidemicus to induce uterine infection. Upon establishment of placentitis, mares were assigned to different therapeutic strategies and responsiveness was monitored. Blood was collected during the third trimester of pregnancy, and relaxin content was determined using a homologous equine relaxin radioimmunoassay. The results reported here show a positive relationship between low circulating relaxin and poor pregnancy outcome in mares with compromised placental function. While relaxin may have value as a diagnostic assay for identifying mares with high‐risk pregnancies associated with placental dysfunction, the variable results obtained from mares undergoing drug treatment for experimentally induced placentitis make it difficult to determine the reliability of relaxin for evaluating therapeutic efficacy.

Relaxin and placental dysfunction in the horse

The equine industry would benefit from a hormonal indicator that reflects placental and fetal well-being in the horse. Pregnancy loss during the third trimester and death of foals weakened by abnormal periparturient events constitute a large percentage of fetal and neonatal mortality [1]. Due to the expense of breeding contracts and the long gestation of the mare, late-term fetal death represents a major financial loss and time investment for the breeder. Early identification of placental insufficiency would make it possible, in some cases, to sustain the pregnancy through medical intervention. Furthermore, aggressive prepartum therapy affords foals a better chance of survival. For example, when placental function is compromised in mares suffering from fescue toxicosis, timely drug therapy rescues the placenta and improves pregnancy outcome [2,3,4,5]. Likewise, if diagnosed early, placentitis can be treated with systemic antibiotics, progestins (progesterone, 17α-hydroxyprogesterone, 5α-pregnanes), non-steroidal anti-inflammatory drugs or steroids (cortisol, to hasten fetal organ maturation).