IN-DEPTH: CONDITIONS AND MANAGEMENT OF THE PERIPARTUM MARE


ditions are considered to be deformations due to ab- normal growth and development caused by a restricted “in-utero” position.49 Deformations appear much more commonly in foals with abnormal presen- tations, such as transverse or caudal presentation. Congenital skeletal deformations may be single or multiple and include wry nose, cervical and thoracic spinal torticollis, and/or scoliosis. These may also be a consequence of abnormal position during vertebral development or occasionally true vertebral malforma- tions. Flexural limb deformities are also a common deformation in foals.50 Other conditions include soft and hard palate defects, brachygnathia, microphthal- mia, hydrocephalus, cerebellar hypoplasia, microen- cephaly, ventricular septal and other cardiac defects, intestinal atresia, omphalocoele, hyperelastosis cutis, and epitheliogenesis imperfecta. There are few etio- logical studies that explain the cause of these defects. The presence of serious fetal defects may result in abortion, stillbirth, or early neonatal demise. Detec- tion and management of deformities is challenging. Premature mammary development and lactation are often the first indicators of impending delivery due to fetal deformity, yet determining the root problem often occurs postpartum. Ultrasound examination and/or Doppler ultrasonography hold the most promise for the early detection of fetal aberrations.


12. Fescue Toxicity


Tall fescue grass, commonly grown in parts of the United States, may be infected with an endophytic fungus (Neotyphodium coenophialum) and when eaten may result in exposure to toxic alkaloids, es- pecially ergovaline. Exposure to endophyte toxins has been associated with problems in late pregnancy including placental thickening, edema, and separa- tion, increased gestational length, stillbirth, dysto- cia, retained placenta, and agalactia. Reduced serum progesterone and prolactin levels are present in the affected mares.51 Foals that survive pro- longed gestation are reported to be emaciated but large-framed and dysmature. Fetoplacental ultra- sonography may detect placental thickening, edema and premature placental separation. This latter finding has been reported to occur a few hours prior to spontaneous delivery in one study on fescue in- fected mares.52 Abnormal fetal growth and other biophysical parameters indicating compromised fe- tal wellbeing should also be assessed.


13. Prolonged Pregnancy


“Prolonged” pregnancy more commonly reflects vari- ation in normal gestational length (usually consid- ered to be about 320–365 days) that occurs in the mare associated with a variety of factors including foaling month of the year (related to photoperiod), foal sex, breed, and intrinsic genetic factors related to the individual. Most mares deliver foals within a repeatable gestational length, plus or minus a few days. Occasionally, underlying maternal/fetal ab- normality may be responsible, such as fescue toxico-


138 2019  Vol. 65  AAEP PROCEEDINGS


sis, pituitary defects, placental atrophy and hypoplasia, and other causes of placental insuffi- ciency.53 Placental hypoplasia and insufficiency af- fect fetal growth and development while also prolonging gestation with the fetus essentially grow- ing at a much slower pace. This may result at full-term delivery of a small and undersized fetus. Although the 2D ultrasound assessment of fetal size is limited by the large size of the late-term equine fetus, useful measurements can be made to assess whether substantial differences in size are present to that expected for the known gestational age. A small number of studies have reported serial mea- surements of fetal size in mid-to-late pregnancy us- ing aortic diameter, total orbit dimensions, and thoracic diameters to allow identification of a growth restricted fetus.16–19


14. Abnormal Presentation


Caudal presentation of the equine fetus is relatively uncommon, but was reported as the cause of dysto- cia in 14% of cases presented with dystocia to a referral hospital.54 In the same study, 10% of mares with dystocia were attributed to transverse fetal presentation of which a greater proportion were in draft breeds. Routine late-term ultra- sound examination can be used to confirm normal, cranial fetal presentation after 9 months’ gesta- tion. Transrectal ultrasound examination can be used to identify the fetal cranium and fetal orbits near the pelvic inlet. Transabdominal ultra- sound examination will identify a fetus in cranial presentation in a ventral position by identifying the fetal heart in the mare’s caudal abdomen with the fetal abdominal contents located in the mare’s cra- nial abdomen.


15. Maternal Risk Factors


Although the possible effect on the fetus of a wide range of maternal conditions, such as acute abdom- inal crisis (e.g., gastrointestinal colic/intestinal dis- placements, colitis, uterine torsion, rupture of the prepubic tendon, abdominal wall rupture/hernia), severe maternal disease (e.g., neoplasia, inflamma- tory bowel disease, chronic grass sickness, Cushings disease, Chronic heaves or recurrent airway ob- struction) and severe orthopedic disease (e.g., lami- nitis, septic tenosynovitis, or arthritis) may be obvious, the impact on fetal wellbeing is not well understood.55–62 Studies of fetal physiology in late gestation have shown that the normal metabolic relationship between the mare and her fetus is finely balanced, indicating that equine fetal growth and development will be very sensitive to distur- bances originating from maternal disease. In late gestation, the equine fetus is very reliant on glucose metabolism and has a limited capacity for endoge- nous glucose production and also a limited ability to switch to alternative fuels when glucose availability is suddenly reduced during, for example, the acute maternal fasting that might occur in a severely ill


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